EP1141693A1 - Heat-sensitive medium for separating species in a separator channel - Google Patents

Abstract

The invention concerns a medium comprising an electrolyte wherein is dissolved at least an assembly of block copolymers characterised in that said block copolymers: are present in said electrolyte at a concentration level to provide said medium with the property of reversibly passing from a state of viscosity V1, obtained at a temperature T1, to a viscosity state V2 greater by at least 100 % than V1, obtained at a temperature T2, and comprise in their structure at least: two non-contiguous polymeric segments having in said electrolyte a lower critical solubility temperature (LCST) and having an average number of atoms along their skeleton more than 50; and a polymeric segment soluble in the electrolyte at temperatures T1 and T2. The invention also concerns the use of said medium for separating analytes.

Description

 THERMOSENSITIVE MEDIUM FOR SEPARATION OF SPECIES FROM

WITHIN A SEPARATION CHANNEL.

The present invention relates to the field of separation, identification and / or analysis of particles, molecules or macromolecules, and more particularly of nucleic acids within a channel, for example in a microfluidic system. or more particularly in the context of capillary eiectrophoresis.

Gel electrophoresis has many applications for the separation of charged particles, molecules and macromolecules, and in particular biological macromolecules such as nucleic acids (DNA, RNA, oligonucleotides), proteins, polypeptides, glycopeptides and polysaccharides. A particularly important application is sequencing, that is to say the reading of the genetic code of DNA. It is most often done in flat and macroscopic gels (of the order of 1 to several mm thick), composed of agarose or polyacrylamide. More recently, other gels derived from acrylamide and a whole series of acrylate or methacrylate gels have been proposed to improve this or that property of the gel. In particular, in US Pat. No. 5,164,057, it has been proposed to use polymers having in solution a critical solubility temperature (hereinafter abbreviated LCST in the present application), to control the hydrophilic / hydrophobic character within '' a permanently cross-linked and irreversible gel, used in electrophoresis.

Despite these improvements, planar gel electrophoresis has several drawbacks.

It requires relatively significant manual work for the preparation of the gel, which can only be used once, and for the subsequent disclosure of the migration distances. The reproducibility of experiments from one gel to another is difficult to obtain, since the properties of the gel depend on the exact conditions of the preparation. Given the production of heat linked to the current, fairly low voltages must be used, leading to long separation times. Finally, planar electrophoresis is difficult to automate and quantify. For these different reasons, macroscopic gel electrophoresis tends to be supplanted by techniques in which the separation or more generally the analysis of the constituents of a sample is carried out in channels of large surface / volume ratio, such as cylindrical capillaries, or channels of planar submillimetric section prepared for within a material (called "chips", microchannels or microfluidic systems). Examples of such separations are described for example in "Capillary electrophoresis in analytical biotechnology", Righetti ed., CRC press, 1996, or in Cheng, J. et al., (1996), Molecular Diagnosis, 1, 183-200.

In what follows, we will designate all the methods involving an electrophoretic separation in a channel or several channels of which at least one dimension is of submillimetric dimension, under the name "capillary electrophoresis" (EC). More generally, the term "microfluidic system" means any system in which the analysis of species is carried out by means of the transport of said species and / or of fluids within a channel or a set of channels, at least one of the dimensions is submillimetric.

CE and microfluidic systems allow faster and more resolving separations than gels, do not require an anti-convective medium, and their properties have been widely used to carry out ion separations in liquid medium.

However, a significant part of the analytes which it is desired to separate by electrophoresis, and in particular those encountered in biology, have, in homogeneous viscous media, a mobility independent of their size and can only be validly separated within an environment with obstacles. The gels used in traditional electrophoresis, in particular, are formed by portions of macromolecular chains or fibers connected to each other and intraversible by the analytes. The latter must work their way along the pores present between the macromolecular segments of the gel, which gives rise to the desired separation. In the first applications of TEC to DNA and proteins, permanent gels crosslinked inside the capillary were often used. This has many disadvantages: the preparation of a very homogeneous and bubble-free gel inside a capillary is delicate. The gel degrades relatively quickly by hydrolysis, and is "polluted" by impurities present in the samples, which end up degrading the performance of the separation, or even by plugging the capillary after a limited number of separations. Given the cost price and / or the difficulty of manufacturing a gel-filled capillary, this defect makes the cost of this approach prohibitive.

At present, the vast majority of separations of biological macromolecules carried out in EC use solutions of entangled linear water-soluble polymers having the advantage of being able to be replaced as often as necessary. At a fairly high concentration, that is to say significantly above the entanglement threshold, the various polymers of the solution become entangled and constitute a continuous transient network of topological obstacles which cannot be crossed by the analytes, thus giving the solution properties. electrophoretic separation.

These solutions of water-soluble polymers give satisfaction in certain applications, but also have many limitations.

The first of these limitations is electroosmosis, an overall movement of the separation medium due to the presence of charges on the walls of the capillary or canal. As this movement is often variable over time and non-uniform, it affects the reproducibility of the measurements and the resolution. Many methods have been proposed to combat it, such as the treatment of the surface of the capillaries by adsorption of essentially neutral species on the walls of the separation channel before the separation proper (Wiktorowicz et al., Electrophoresis, 11, 769, 1990, Tsuji et al., J. Chromatogr. 594, 317 (1992), or by treating the capillary with an acid solution (Fung et al., Anal. Chem. 67, 1913, (1995)). the advantage of being inexpensive and of being able to be repeated several times to regenerate a capillary, but often only reduce electroosmosis only partially. It has also been proposed methods of irreversible grafting of an essentially neutral polymeric layer on the walls , as for example described in US 4 680 201. Ready-to-use treated capillaries are thus commercially available. These capillaries treated irreversibly lead to good reduction of electroosmosis for a certain number of separations but their lifespan is limited and their cost high. Another major drawback of electrokinetic separations in polymer solutions is that the resolution and the separable size range are better with relatively concentrated solutions and high molecular weights (Mitnik et al., J. Chrom. A, 710, 309 (1995 ); Goetzinger et al., Electrophoresis, 19, 242, 1998)). This is attributed to deformations of the separation matrix which limit the resolution for large analytes and which are all the more important the smaller the molecular mass of the matrix and the lower its concentration. On the other hand, the viscosity of a polymer solution increases very quickly when the molecular mass and the concentration are increased. We are therefore limited in the application of solutions of water-soluble polymers entangled by the very great difficulty, and ultimately the impossibility, that there is to introduce into a capillary of small dimensions (typically less than 100 micrometers) a solution very high viscosity. Finally, it should be noted that the separation range accessible to capillary electrophoresis can be extended to larger sizes by the use of pulsed fields. We then come up against DNA aggregation phenomena which limit the scope of the improvement, and which are also all the stronger the lower the viscosity of the medium.

In order to resolve the dilemma posed by the search for a low viscosity for the injection of the separation medium into the canal, and resistant topological obstacles for the separation, which in fact lead to a high viscosity, certain authors have proposed d '' use a polymer medium whose viscosity decreases sharply during a temperature rise. This type of medium has the advantage of allowing the injection of said medium into the capillary at high temperature in a state of low viscosity, and the separation at lower temperature in a state of higher viscosity having good separation performance, like this is commonly performed in gel electrophoresis, in particular with agarose. In applications WO 94/10561 and WO 95/30782, in particular, media are proposed which allow easier injection by raising the temperature. Are essentially described in these patent applications microgels capable of reducing volume at high temperature (thus leading to a dilute solution of discontinuous particles of low viscosity) and to swell at low temperature until completely occupying the separation channel (thus giving the medium a gelled character and good separation properties). However, these separation media have a viscosity which decreases more or less rapidly with temperature: it is therefore necessary to introduce them into the capillary at a temperature higher than the temperature at which the separation takes place, which may have various disadvantages. On the one hand, in capillary electrophoresis devices, it is very difficult to thermostate the entire capillary, and it is therefore difficult to automatically implement a polymer which would only be injectable at a temperature much higher than Room temperature. One could envisage a solution which is not very viscous at room temperature, and which has a high viscosity and good separation properties at a lower temperature, but this implies carrying out the separations at low temperatures, which is not possible. for all analytes. In particular, it is known that for DNA sequencing, an optimal resolution of the "compressions" is obtained at relatively high temperature (of the order of 50-60 ° C.), which is incompatible with the preceding principle. Application WO 98/10274 proposes for its part a molecular separation medium comprising at least one type of block copolymer which is in solution at a first temperature and in a gel type state at a second temperature. This medium also comprises a buffer which has the role of dissolving the block copolymer at a first temperature, and of making it transit towards the gel state at said second temperature without interrupting the separation process, and without preventing the return to a soluble state when returning to said first temperature. More specifically, the polymers described are triblock polymers of low molecular weights (typically less than 20,000), of the polyoxyethylene-polyoxypropylene-polyoxyethylene family (POE-POP-POE) and more specifically still (POE ₉₉ -POP ₆₉ -POE ₉₉ , where the indices represent the numbers of monomers of each block) (trade name "Pluronic F127). At low temperature, the two POE segments at the end of the triblock systems are water-soluble, and given the low molecular weight of the copolymer, the solutions are relatively low in viscosity up to a high concentration. By raising the temperature to around 15-25 ° C, the central central POP segment becomes more hydrophobic, and these polymers combine to form within the medium a three-dimensional organized network of predetermined structure, which gives the medium the appearance and the consistency of a gel. Unfortunately, this mechanism has several drawbacks for electrophoresis. On the one hand, it gives rise to a gel state endowed with good electrophoretic separation properties only at high polymer concentrations, greater than 15 g / 100 ml or even 20g / 100ml, which leads to high friction and to long migration times. Furthermore, the dependence of the properties as a function of the rate of temperature change makes the reproducibility of the results random. Finally, the products proposed in WO 98/10274 have a low viscosity either below ambient temperature or above ambient temperature, and exhibit an advantageous gel state for the electrophoretic separation in the vicinity of ambient temperature (25 ° C. ), which is neither interesting for conveniently filling the capillaries, nor for applications such as DNA sequencing.

Triblock copolymers having the same structure, with different molecular weights, give rise to comparable physical properties and to separation performances comparable to or less than F127. Is also described in WO 98/10274 a type polymer POB ₁₂ - ₂₆₀ POE -POB ₁₂ wherein POB means polyoxybutylene. Unlike the previous polymers, these polymers give rise to a low viscosity state at a temperature above room temperature, and to gelling by lowering of temperature in the vicinity of room temperature.

It should be noted that there are other polymers which may present in water a thermoviscosifying or thermo-thickening character. In patent application EP 583 814 are described thermoviscosifying polymers, which contain on the one hand hydrophilic parts of the prepolymer or macromonomer chain type which do not have LCST in a useful temperature range, and on the other hand parts hydrophilic of the prepolymer chain type or macromonomers which have an LCST in the said useful temperature range. However, polymers of this type cannot be used with good performance as a separation medium for electrophoresis, for several reasons. On the one hand, they exert their thermoviscosifying effect only in the presence of a relatively large amount of salt in the solution, of between about 0.4 M and several M. This property is very disabling for the electrophoresis, because the use of highly saline solutions leads to heating of the solution and prohibits the use of strong electric fields. Separations in highly saline environments are therefore slow and not very resolving. On the other hand, they have an electrically charged skeleton: if one wishes to use them as an electrophoretic separation medium, the polymers constituting the matrix themselves risk being set in motion, or giving rise to electroendosmosis, disturbing the separation that we wanted to obtain by interaction between the analytes and fixed obstacles. Thirdly, these media are provided to give rise to thermoviscosification, or to maintain an approximately constant viscosity, in a single and relatively wide temperature range including the LCST of said hydrophilic parts with LCST. However, it would be particularly advantageous for electrophoresis to have two very distinct useful temperature ranges, one for injecting the separation medium into the capillary, and the other for the electrophoretic separation proper, the said separation taking place while the medium is maintained at an approximately constant temperature.

In fact, most of the synthetic media proposed until now as being able to give rise to a thermoviscosifying effect have a charged skeleton (L'alloret et al., Colloid. Polym. Sci., 273, 1163-1173 (1995), Hourdet , Polymer preprints, 34, 972-973 (1993), Hourdet et al., Polymer, 38, 2535-2547 (1997)). Indeed, a usual way to confer thermosiscosifying properties on a polymer consists in constructing a molecule having portions of hydrophilic chains at any temperature which help to maintain the molecule in solution, and portions of chains with LCST which lead by raising of temperature to an attractive interaction between chains, responsible for viscosification. To obtain good viscosification, it would be desirable to multiply the proportion of the portions of LCST chains and their interaction force, but such an increase tends also to induce a macroscopic phase separation, which on the contrary reduces the viscosity. The presence of electrical charges on the skeleton helps to prevent the separation of macroscopic phases by effect of entropy of the counter-ions or electrostatic repulsion, and thus makes it possible to bring into the composition of the polymers a quantity of portions with LCST sufficient to give viscosification, while preventing macroscopic phase separation. It can therefore be seen that it is particularly difficult to constitute thermo-viscous media based on polymers with neutral hydrophilic skeleton. Some examples of such media have been described in de Vos et al., Polymer, 35, 2644 (1994), but they do not give rise to thermoviscosification except in the presence of a high salt content and at temperatures of more than 80 ° C, which also makes them unusable for most possible applications as a separation matrix, and in particular for electrophoresis.

Consequently, although many types of medium, heat-sensitive or not, have been proposed as matrices for the electrokinetic separation of species within a channel, and many types of heat-sensitive medium have also been proposed for others. applications, there are currently no media with optimal properties for said separations. The object of the present invention is precisely to propose a new type of separation media, the properties of which can be optimized as a function of the size of the analytes which it is desired to separate through the selection of a specific copolymer. .

For the purposes of the invention, the term “separation” is intended to cover any method aiming to separate, identify or analyze, all or some of the species contained in a mixture, the said species being commonly called "analytes".

This separation can thus be carried out within a channel in a microfluidic system or in the context of electrophoresis.

The invention is particularly advantageous in the case of electrokinetic separations. The expression electrokinetic separation is intended to cover any method aiming to separate all or some of the species contained in a mixture, the said species being commonly called "analytes", by causing them to migrate within a medium under the action of an electric field, whether the field exerts its motive action on the analytes directly or indirectly, for example by means of a displacement of the medium itself, as in electrochromatography, or a displacement ancillary species such as micelles, in the case of micellar electrochromatography, or by any combination of direct and indirect actions. A method of electrokinetic separation according to the invention will also be considered any method of separation in which the said action of the electric field is combined with another driving action of non-electric origin.

More particularly, the subject of the present invention is a thermosensitive medium for the separation of species within a separation channel, said medium comprising an electrolyte in which at least one set of block copolymers is dissolved, characterized in that said block copolymers :

- are present in said electrolyte at a sufficient concentration to give said medium the ability to reverse reversibly from a state of viscosity V1, obtained at a temperature T1, towards a state of viscosity V2 at least 100% higher than V1, obtained at a temperature T2 at least 20 ° C higher than T 1 and

- include in their structure at least:

- two non-contiguous polymer segments having an LCST in said electrolyte and having an average number of atoms along their skeleton greater than 50 and

- a polymer segment soluble in the electrolyte at temperatures T1 and T2.

Under the invention, unless explicitly stated, all the means on sets of chains or on sets of polymeric segments, such as the average molecular mass, or the average number of atoms along the skeleton, or even the average number of grafts in the case of a comb polymer, are understood as mass averages in the usual sense of polymer physics.

The claimed separation medium therefore has the capacity to pass reversibly between a fluid state of low enough viscosity to allow its introduction into the said channel, obtained at a temperature T1, and a significantly higher state of viscosity, and in any state of cause at least twice higher, obtained at a temperature T2 at least 20 ° C higher than the temperature T1. At temperature T2, said separation medium is endowed with significant separation properties for species in a range of predefined chemical composition and size.

By "temperature T1" is meant in the context of the invention, either a precise temperature, or a relatively narrow temperature range, typically of the order of 10 ° width, useful for the execution of an operation particular relating to the separation process, and in particular for the introduction of the separation matrix according to the invention into the separation channel. According to a preferred variant of the invention, the temperature T1 is between approximately 15 and 30 ° C. Likewise, by "temperature T2" is meant in the context of the invention, either a precise temperature or a relatively narrow temperature range, typically of the order of 10 ° width, useful for carrying out another specific operation relating to the separation process, and in particular for the step of separation of the analytes within the channel. According to a preferred variant of the invention, useful for DNA sequencing, this temperature or temperature range T2 is between approximately 40 and 80 ° C. According to a preferred variant of the invention, the LCST of a significant fraction of said segments having an LCST is between temperatures T1 and T2 and more preferably between about 20 and 50 ° C.

For the purposes of the invention, the term “electrolyte” is intended to denote a condensed medium capable of conducting ions. In the most common case, this medium is an aqueous buffered medium, such as buffers based on phosphate, ths (hydroxymethyl) aminomethane (TRIS), Borate, N-tris (hydroxymethyl) methyl-3-aminopropane sulfonic acid (TAPS), histidine, lysine, etc. Many examples of buffers usable in electrophoresis are known to those skilled in the art, and a number of them are described, for example, in "Sambrook et al.," Molecular Cloning: a laboratory manual ", Cold Spring Harbor Lab, New York, 1989. However , all types of electrolyte can be used in the context of the invention, in particular hydroorganic solvents such as, for example, water-acetonitrile, water-formamide or water-urea mixtures, polar organic solvents such as, also for example example, N-methylformamide. Particularly useful in the context of the invention are the so-called "sequencing buffers" electrolytes, consisting of an aqueous buffer at alkaline pH added with a significant proportion of urea and / or formamide .

For the purposes of the invention, the term “species” is intended to denote generally analytes. These analytes can be particles, organelles or cells, molecular or macromolecular species, and in particular biological macromolecules such as nucleic acids (DNA, RNA, oligonucleotides), nucleic acid analogs obtained by chemical synthesis or modification, proteins , polypeptides, glycopeptides and polysaccharides for which total or partial separation is desired during their electrokinetic migration within said separation medium.

For the purposes of the invention, the term “polymer segment” or “segment” is intended to denote a set of monomers linked together covalently and having specific physicochemical properties, in particular as regards solvation. An example of a polymer segment within the meaning of the invention is given by a sequence of all identical monomers (homopolymer segment), or a copolymer having no significant composition correlation over lengths of more than a few monomers (segment of random copolymer type ).

For the purposes of the invention, the term “block copolymer” is intended to denote a copolymer consisting of polymer segments of significantly different compositions, covalently linked together. The block copolymer is defined by the fact that each of the segments comprises a sufficient number of monomers to present within the electrolyte physicochemical and in particular solvation properties, comparable to those of a homopolymer of the same composition and of the same size. . He opposes the polymer statistical, in which the different types of monomers succeed one another in an essentially random manner, and locally confer on the chain global properties, different from those of the homopolymers of each of the species in question. The size of the homopolymer segments necessary to obtain this block character can vary depending on the types of monomers and of the electrolyte, but it is typically a few tens of atoms along the skeleton of said segment. It should be noted that a block copolymer can be constituted within the meaning of the invention, in which part or all of the segments are themselves constituted by a copolymer of statistical type, insofar as one can distinguish within the said block copolymer of zones or segments of sufficient size and difference in chemical composition to give rise from one segment to another to a significant variation in the physicochemical properties and in particular of solvation. Finally, the term “non-contiguous polymer segments” is intended to denote within a block polymer two segments linked together by a polymer segment of different nature.

Block copolymers suitable for the invention have the particularity of combining in their structures, at least two types of segments.

The first type of segment is soluble in the electrolyte used for the separation at two temperatures T1 and T2 of use of the claimed medium and preferentially does not present in said LCST electrolyte.

In the present text, the term “soluble” is intended to refer to a solubility in the electrolyte at temperatures T1 and T2.

In contrast, the second type of segment has an LCST in the electrolyte used for separation. More specifically, this type of segment is essentially soluble in said electrolyte in a range of low temperatures, and essentially insoluble in said electrolyte in a range of high temperatures. The limit between these two temperature ranges is called "minimum demixing temperature" or more commonly "LCST".

Due to the presence of these LCST segments in their structure, the copolymers used according to the invention have the property of constituting, at low temperature, a macroscopically entangled solution. homogeneous, within which the interactions between different molecules of polymers are essentially repulsive and give rise, following a rise in temperature, to attractive interactions between some of their parts which reinforce the interactions of entanglement between chains. According to a preferred embodiment of the invention, the average number of LCST segments per copolymer is greater than 2 and preferably greater than 5, and more preferably still between 8 and 40. Thanks to this large number of segments, capable of interacting attractively, a given copolymer can interact with many other copolymers, which gives the medium a high resistance during the passage of analytes.

The length and the number of LCST segments present in the copolymers used in the media according to the invention, as well as their chemical nature, can therefore vary significantly within the scope of the invention, and it is thus possible to vary greatly the viscoelastic properties of said media according to the desired application, as will be shown more precisely in the presentation of examples of implementation.

The media according to the invention are therefore suitable for obtaining heat-thickening properties. Within the meaning of the invention, the term “thermo-thickening” means having either a thermo-viscosifying character or a thermo-gelling character.

In accordance with common usage, the term "thermosetting" means a medium remaining in the range or ranges of use temperature capable of flow in a macroscopic container, in a time compatible with easy handling, ie less than around 30 seconds. On the contrary, the term "gel type state" means a medium incapable of significant flow under the same conditions.

Equivalently, thermoviscosifier is called a medium which does not have in the temperature range (s) of use hysteresis of their properties, or of significant dependence on its properties as a function of the rate of temperature change, for rates of temperature change usually and conveniently used in capillary electrophoresis, that is to say of the order of 1 degree per minute to ten degrees per minute. We will call by opposition "thermogelling medium", or so equivalent "medium giving rise to a gel-like state", a medium having under these conditions a hysteresis of its properties or else having a viscosity greater than 20,000 cp.

According to a preferred variant, particularly suitable for the case of automated methods in which it is desired to minimize the time between two consecutive separations, the medium according to the invention will be of the thermoviscosifier type.

According to another variant, preferred when a long waiting time between separations is acceptable, and when one seeks maximum resistance of the matrix to the passage of the analytes, on the contrary, one will prefer a medium according to the invention giving rise to the temperature T2 at a gel-like state.

According to a preferred embodiment of the invention, all or part or a significant fraction of the LCST segments have, along their skeleton, an average number of atoms greater than 75, or have a molecular mass greater than 2500, and preferably greater at 4500.

For the purposes of the invention, the term "a significant fraction", or in shorthand by "all or part", means a proportion sufficient to give rise by increase in temperature to an increase in viscosity of at least 100% or equivalent to multiplying the viscosity by a factor of 2.

Copolymers optimized for the implementation of the invention are especially those in which all of the LCST segments represent between 2 and 25% by mass, preferably between 5 and 15% by mass and even more preferably between 8 and 15% by mass of the average total molar mass of said copolymers, or between 3 and 20% and preferably between 5 and 10% of the total composition of the copolymers in number of moles of monomers.

The claimed separation medium can advantageously comprise a set of block copolymers, comprising a skeleton constituted by a segment or a multiplicity of segments, of a chemical nature. identical or different, and having the common characteristic of being essentially soluble or else solvated in the electrolyte at temperatures T1 and T2, to which are covalently linked a multiplicity of segments of identical or different chemical nature and having the common character of be essentially soluble or else solvated in the electrolyte at temperature T1, and essentially insoluble or poorly solvated in the electrolyte at temperature T2.

All kinds of structures of copolymers of this type can be used for the implementation of the invention, provided that they have a multiplicity of segments with LCST not directly connected, and give rise to a reversible thermo-thickening under the conditions of separation.

By way of illustration of the various structures capable of being adopted by the copolymer according to the invention, mention may be made particularly of those where all or part of said copolymers are present: - in the form of a linear block polymer,

- in the form of a comb copolymer, the backbone of which consists of one or more segments soluble in the electrolyte at temperatures T1 and T2 or else

- in branched form. In the linear block polymer structure, the segments to

LCST are present in a number greater than 2 and are separated from each other along an essentially linear skeleton by segments of polymer not exhibiting LCST. The length of these latter segments may be, in the context of the invention, or relatively uniform, or on the contrary variable, the latter variant being preferred.

In fact, it is particularly advantageous to choose a block polymer of the comb polymer type, with a skeleton essentially soluble in the electrolyte at temperatures T1 and T2, carrying a multiplicity of side links essentially soluble in the electrolyte at temperature T1 and insoluble in the electrolyte at temperature T2. According to a preferred mode of implementation, the so-called lateral links with LCST are arranged along the skeleton in a random or non-regular manner. This mode of implementation is generally preferable to the opposite structure, which would include polymers consisting of a main chain consisting of LCST segments carrying hydrophilic grafts, insofar as a polymer of this second type contracts above LCST and thus cannot give rise to the continuous network of topological obstacles necessary for the implementation of the invention.

It should be noted that the invention could not be implemented with block polymers consisting of segments soluble in the electrolyte and hydrophobic segments without LCST, since such polymers give rise to thermofluidification.

Particularly advantageous in the context of the present invention are separation media in which at least one of the following conditions is satisfied:

- all or part of the copolymers have an average number of atoms, along a section of soluble segment comprised between two consecutive bonding points of said soluble segment with segments with LCST, greater than 210;

- all or part of the copolymers have a molecular mass greater than 30,000 or a number of atoms along the main skeleton greater than 2,000 and

- all or part of the copolymers have a molecular mass of between 50,000 and 3,000,000 or a number of atoms along the main skeleton of between 2,500 and 100,000 and / or

- The average number of LCST segments per chain is greater than or equal to 4, and preferably between 5 and 100.

It is particularly advantageous for the implementation of the invention to use copolymers in which the segment or segments soluble at temperatures T1 and T2 consist of at least one polymer chosen from polyethers, polyesters such as polyglycolic acid, soluble homopolymers and random copolymers of the polyoxyalkylene type such as polyoxypropylene, polyoxybutylene, polyoxyethylene, polysaccharides, polyvinyl alcohol, polyvinylpirrolidone, polyurethanes, polyamides, polysulfonamides, polysulfoxides, polystyrenesulfonate, polyacrylamide derivatives and polymethacrylamides substituted or insoluble in said electrolyte.

As a representative of the polyacrylamides and polymethacrylamides, mention may very particularly be made of polyacrylamide, polyacrylic acid, poly N, N-dimethylacrylamide and polyacryloylaminopropanol.

Of course, other polymers soluble in the electrolyte can be used according to the invention as soluble segments, depending on the particular application and the ease of introducing them into a block polymer of desired structure.

It is more generally advantageous that the soluble segments have a high solvation in the electrolyte at the two temperatures T1 and T2.

Many types of polymers can be chosen to constitute the segments which are not contiguous to LCST within a block copolymer which can be used according to the invention, depending on the electrolyte envisaged, the temperatures T1 and T2 preferred for use and analytes to be separated. Many LCST polymers are known to those skilled in the art, in particular in an aqueous medium. It is thus possible to refer to the book "Polymer Handbook" Brandrupt & Immergut, John Wiley, New York.

According to a preferred variant of the invention, all or part of the LCST polymer segments are derived from one or more polymers chosen from:

- polyvinylalkyl ether such as polyvinylmethylether,

- hydroxyalkylcelluloses such as hydroxyethylcellulose and methylcellulose,

- homopolymers of etheroxides such as polyoxyalkylenes such as polyoxypropylene and polyoxybutylene, - random and block copolymers of etheroxides such as polyoxyalkylene type copolymers having an LCST such as polyoxyethylene / polyoxypropylene and polyoxyethylene / polyoxybutylene,

- alkylene homo- and co-polymers such as butylene-propylene, ethylene-propylene and ethylene-butylene and

polyacrylic derivatives derived from the homopolymerization or copolymerization of monomers chosen from acrylic and methacrylic acids, alkyl acrylates and methacrylates such as hydroxypropyl and hydroxyethyl acrylates, N-alkyl-acrylamides or -methacrylamides such as N-ethylacrylamide, N-isopropylacrylamide, N 'N-dialkyl -acrylamides or -methacylamides, aryl-acrylamides or -methacrylamides and alkylaryl-acrylamides or -methacrylamides.

More preferably, the copolymer used according to the invention comprises at least two non-contiguous segments with LCST property derived from the homo- or co-polymerization of monomers chosen from acrylic and methacrylic acids, N-alkyl-acrylamides or - methacrylamides such as N-ethylacrylamide, N-isopropylacrylamide, aryl-acrylamides or -methacrylamides and alkylaryl-acrylamides or -methacrylamides.

Thus, by way of example and in a non-exhaustive manner, it is possible to use, as LCST segments, N-isopropylacrylamide (NIPAM), N-isopropylmethacrylamide, N, N'-diethylacrylamide, or random copolymers of these monomers between them or with others.

The following copolymers are particularly suitable for the invention:

- copolymers of the comb copolymer type, the backbone of which is of the acrylamide, acrylic acid, acryloylaminoethanol or dimethylacrylamide type and at the level of which lateral segments of the poly (N-alkyl or N, N dialkyl) acrylamide type, preferably of the poly type, are grafted (N isopropylacrylamide), or side segments of the polyoxypropylene type or polyoxyethylene / oxypropylene copolymer, statistical or block, or more generally side segments of polyether type significantly more hydrophobic than polyoxyethylene

- copolymers of the block copolymer type and having, along their backbone, alternating segments of polyoxyethylene type and segments of polyoxypropylene type, or alternating segments of polyoxyethylene type and segments of polyoxybutylene type or more generally alternating segments of polyethylene and polyether type segments which are notably more hydrophobic than polyoxyethylene.

By way of examples, copolymers chosen from polyacrylamide / poly (N-isopropylacrylamide) (PAM-NIPAM) can be used as copolymers in the claimed separation medium; polyvinyl alcohol / poly (N-isopropyl-acrylamide) (PVA-NIPAM), polyoxyethylene / polyoxypropylene, polyacrylamide / oxyethylene-oxypropylene copolymer, polyacrylamide / polyoxypropylene, polyacrylic acid / polyoxypropylene, polyacrylic acid / polyyric acid / polyoxypropylene copolymer -isopropylacrylamide) and polydimethylacrylamide / poly (N-isopropylacrylamide) (PDMAM-NIPAM).

It is advantageously possible to use a medium comprising a comb copolymer carrying, along a polyacrylamide skeleton, segments with LCST essentially consisting of poly-NIPAM, and comprising along their skeleton a number of carbon atoms between 35 and 600, and whose fraction by total mass does not exceed 25%.

It should also be noted that in the majority of applications, and in particular for separating charged analytes, it is preferable to use a polymer according to the invention which is essentially neutral. It may however be useful for certain applications, and in particular for separating lightly or uncharged analytes, or tending to associate with the polymer, to choose a polymer according to the invention deliberately charged. Polymers of this type can be conveniently prepared, for example by including in the segments soluble in the electrolyte at temperatures T1 and T2 a significant portion of polymerized acrylic acid. A copolymer of this type is more particularly described in Example 10 below. As regards more particularly the concentration of copolymer in the medium, it is generally less than 20 g / 100 ml by weight. For DNA sequencing applications, it is preferably between approximately 1 and 8 g / 100 ml by weight. According to a particular embodiment of the invention, the copolymers used in said medium are advantageously capable, from a concentration of the order of 5 g / 100 ml and preferably of the order of 2 g / 100 ml, by weight of making reversibly transiting said medium from a state of viscosity V1, obtained at a temperature T1, to a state of viscosity V2 at least 100% higher than V1, obtained at a temperature T2 at least 20 ° C higher than T 1 .

Also, according to a preferred variant of the invention, the viscosity V2 is greater by at least a factor of 5 than the viscosity V1.

As regards the preparation of the copolymers used according to the invention, it can be carried out by any conventional technique of polymerization or polycondensation. The choice of the preparation method is generally made taking into account the desired structure for the copolymer, namely comb, linear or branched and the chemical nature of the various blocks constituting it. By way of representative of these preparation variants, mention may very particularly be made of the processes according to which said copolymers are obtained by:

- polycondensation, polymerization or copolymerization, ionic or radical, of identical or different monomers, of identical or different macromonomers, or of a mixture of identical or different monomers and macromonomers or

- By grafting of several LCST polymer segments on a linear or branched polymer backbone essentially of the soluble type, or by polymerization of LCST polymer side segments from a linear or branched polymer backbone of the essentially soluble type.

Preferably, all or part of the copolymers used according to the invention are obtained by: a) copolymerization of monomers essentially of the soluble type and of macromonomers essentially of the LCST type comprising at at least one of their ends a reactive function, or

b) copolymerization of macromonomers essentially of the LCST type comprising at least one of their ends a reactive function, and of macromonomers essentially of the soluble type comprising within their structure at least one reactive function.

Within the meaning of the invention, the term reactive function means a group allowing the molecule carrying this group to be integrated into the macromolecule during the copolymerization reaction without interrupting said copolymerization.

With the aid of the rules and preferred methods set out above, those skilled in the art are capable of preparing copolymers in accordance with the invention, by adapting the structure, the nature and the method of preparation of said polymers according to the separation properties sought for one application or another.

As a representative but not limiting of the claimed separation media, mention may be made of the following media: - the media passing through with a viscosity V1 of between 50 and 1000 mPa m ^"1 s ^{" 1} at a temperature T1 of between 15 and 30 ° C towards a viscosity V2 greater than V1 by a factor of between 2 and 50 at a temperature T2 of the order of 40 ° C or higher and comprising between 5 g / 100ml and 20 g / 100ml of copolymers having - a average molecular weight between 30,000 and

2,000,000 or a number of atoms along the main skeleton is between 1,000 and 60,000,

- a mass fraction of LCST segments between 2% and 20%, and - an average molecular weight of LCST segments between 2,000 and 20,000 or an average number of atoms along a segment with LCST between 35 and 350; - media passing through with a viscosity V1 of between 100 and 10,000 mPa m ^"1 s ^{" 1} at a temperature T1 of between 15 and 30 ° C to a viscosity V2 greater than V1 by a factor of between 2 and 100 to a temperature T2 greater than 40 ° C and comprising between 1 g / 100ml and 8g / 100ml of copolymers having:

- an average molecular mass of between 500,000 and 5,000,000 or a number of atoms along the main skeleton of between 7,000 and 90,000,

- a mass fraction of LCST segments between 2.5% and 15%, and

- an average molecular weight of LCST segments between 4,000 and 30,000 or an average number of atoms along an LCST segment between 60 and 600; and

- media passing through with a viscosity V1 of between 100 and 10,000 mPa m ^"1 s ^{" 1} at a temperature T1 of between 15 and 30 ° C to a viscosity V2 greater than V1 by a factor of between 2 and 100 to a temperature T2 of the order of 40 ° C or higher and comprising between 0.1 g / 100ml and 5 g / 100ml of copolymers having

- an average molecular mass greater than 500,000 or a number of atoms along the main skeleton greater than 7,000,

- a mass fraction of LCST segments between 2% and 15%, and

- an average molecular weight of the LCST segments greater than 4,000 or an average number of atoms along an LCST segment greater than 90.

In the present description, the viscosity is that obtained at a shear rate of 10 s ⁻¹ .

It is also possible, in the context of the invention, to include in the separation medium, in addition to the copolymer (s) with heat-thickening character, other species which do not have these properties, such as in particular water-soluble polymers, polymers non-heat-thickening associatives, or neutral or ionic surfactants, to the provided that these adjuvants do not give rise to demixing within the separation medium or to a loss of the reversible thermo-thickening character. Such adjuvants can be advantageous for modulating the properties and / or the separating power of said medium. It is in particular known that the addition of certain surfactants can in certain cases strengthen the association between polymers, and therefore the thermo-thickening character. It may also be advantageous to add associative or non-low molecular weight polymers to the medium, in order to improve the separation of the smallest analytes contained in a mixture without seriously affecting the overall viscosity, as is known in contexts different from that of the invention.

The present invention also relates to the use of a separation medium as defined above for the separation or the analysis of species chosen from molecular or macromolecular species, and in particular biological macromolecules such as nucleic acids. (DNA, RNA, oligonucleotides), nucleic acid analogs obtained by chemical synthesis or modification, proteins, polypeptides, glycopeptides and polysaccharides, organic molecules, synthetic macromolecules or particles such as mineral particles, latex, cells or organelles.

It is particularly useful for DNA sequencing, for which it makes it possible to obtain optimal separation conditions linked to a high viscosity, at an elevated temperature for which the resolution of the compressions is good and the separation rapid, while retaining at room temperature a moderate viscosity allowing easy DNA injection.

However, the possibility offered by the invention of greatly varying the viscosity of the medium by changing the temperature is also advantageous for other applications.

It is in particular advantageous whenever an increase in the rigidity or the viscosity of the medium contained in a capillary or a microchannel would be desirable. For example, a high viscosity allows reduce the electrohydrodynamic effects responsible for poor separation of large DNA in pulsed field and more generally reduce harmful hydrodynamic flows within a capillary or microchannel. It should also be noted that, although the media according to the invention generally exercise their beneficial effect at best by means of a change in temperature, they are also suitable for use at constant temperature. They can thus lend themselves to introduction into the separation channel and subsequent separation of the analytes at the same temperature. This may be advantageous, in particular if there is an apparatus capable of introducing into the separation channel a medium of high viscosity, and / or not easily allowing to modify the temperature between the introduction of said medium into the channel and separation of the analytes.

Another advantage of the high viscosities authorized by the media according to the invention is that they reduce electroosmosis (see for example Bello et al., Electrophoresis 15, 623, 1994), without the need to resort to d other modes of suppressing electroosmosis known to those skilled in the art, such as for example the use of polymers having an affinity for the capillary wall, or the grafting of neutral hydrophilic polymers on the surface. If the suppression of electroosmosis or of the interaction of the analytes with the walls effected by the media according to the invention is not sufficient for a particular application, one of the methods known from skilled in the art, and thus obtain properties even superior to those obtained with these methods used alone. Advantageously, it is possible to modulate the separating properties of the claimed medium via the selection of a copolymer in accordance with the invention and whose thermo-thickening effect is more particularly optimized for the separation of species of defined sizes.

By way of illustration of this type of accessible adaptation according to the invention, it is possible in particular:

- separate molecules of molecular mass less than 50,000 or oligonucleotides comprising less than 100 nucleotides, or native or denatured proteins with a transit medium of viscosity V1 between 50 and 1000 mPa m ^"1 s ^{" 1} at a temperature T1 between 15 and 30 ° C towards a viscosity V2 greater than V1 by a factor between 2 and 50 at a temperature T2 of the order of 40 ° C or higher and comprising between 5 g / 100 ml and 20 g / 100 ml of copolymers having: - an average molecular weight of between 30,000 and

2,000,000 or a number of atoms along the main skeleton is between 1,000 and 60,000,

- a mass fraction of LCST segments between 2% and 20%, and - an average molecular weight of LCST segments between 2,000 and 20,000 or an average number of atoms along a segment with LCST between 35 and 350,

- separating DNA sequence reaction products, duplex DNAs of less than 1000 base pairs, denatured proteins or synthetic or natural polymers of molecular mass between 20,000 and 10,000,000 with a medium passing through a viscosity V1 between 100 and 10,000 mPa m ^'1 s ^"1 at a temperature T1 between 15 and 30 ° C towards a viscosity V2 greater than V1 by a factor between 2 and 100 at a temperature T2 greater than 40 ° C and comprising between 1 g / 100ml and 8g / 100ml of copolymers having:

- an average molecular mass of between 500,000 and 5,000,000 or a number of atoms along the main skeleton of between 7,000 and 60,000, - a mass fraction of LCST segments of between 2,5% and 15%, and

- an average molecular weight of LCST segments between 4,000 and 30,000 or an average number of atoms along an LCST segment between 60 and 600 or

- separate duplex DNA of size between 500 bases and several million base pairs, or particles such as latex, whole cells, whole chromosomes or organelles with a medium transiting from a viscosity V1 between 100 and 10,000 mPa m ^"1 s ^{" 1} at a temperature T1 between 15 and 30 ° C to a viscosity V2 greater than V1 by a factor between 2 and 100 at a temperature T2 of the order of 40 ° C or higher and comprising between 0.1 g / 100ml and 5 g / 100ml of copolymers having:

- an average molecular mass greater than 500,000 or a number of atoms along the main skeleton greater than 7,000,

- a mass fraction of LCST segments between 2% and 15%, and - an average molecular mass of the LCST segments greater than 4,000 or an average number of atoms along an LCST segment greater than 90.

More preferably, these media comprise a set of copolymers chosen from:

- copolymers of the comb copolymer type, the backbone of which is of the acrylamide, acryloylaminoethanol or dimethylacrylamide type and to which side chains of the poly (N isopropylacrylamide) type are grafted and

- copolymers of the block copolymer type and having, along their backbone, an alternation of polyoxyethylene type blocks and polyoxypropylene type blocks, or an alternation of polyoxyethylene type blocks and polyoxybutylene type blocks or more generally an alternation of blocks of soluble polyoxyalkylene type and polyoxyalkylene blocks with LCST.

By way of illustration of the mode of use of the claimed separation medium, one can in particular propose that comprising:

- the selection of a separation medium according to the invention, according to the characteristics of the species to be separated; the introduction of this medium into a separation channel of an electrophoresis device in an amount sufficient to constitute the separation medium; - bringing a significant portion of the channel to temperature T2, either before or after the introduction of a sample;

- the introduction at the inlet of the separation channel of a quantity of sample; - carrying out the separation at a temperature of the order of T2 in the part of the thermostatically controlled channel; and

- detecting the migration of the analytes initially contained in the sample.

This detection uses conventional techniques which fall within the competence of a person skilled in the art and will therefore not be detailed in the present description.

It should be noted that the use of the claimed medium also covers the variants in which the temperature is modified during the separation step, insofar as said temperature variation comprises a temperature or a range of temperatures T2 at which heat-thickening of the medium is carried out as defined above, as well as the variants in which the above cycle is repeated any number of times, preferably automatically.

In fact, the invention is particularly advantageous in the case of automated electrokinetic separations, since it allows automatic filling of the separation channel more easily and more quickly. Furthermore, the introduction of the sample can be, in the context of the invention, carried out before, during or after the heating of a significant portion of the separation channel at temperature T2. The present invention also relates to capillary electrophoresis devices, including those on chips using as a separation medium a medium according to the invention. It is particularly useful in the case of so-called "on-chip" electrophoresis devices or in etched microchannels, since, in general, these devices more easily tolerate the application of high pressures for the introduction of the separation medium than the cylindrical capillaries.

The media according to the invention and the separation methods involving these media are particularly advantageous for the applications of diagnostic, genotyping, and high throughput screening, quality control, or for detecting the presence of genetically modified organisms in a product.

The figures and examples given below are presented by way of illustration and without limitation of the present invention.

Figures

Figure 1: Evolution of the viscosity as a function of temperature for different PAM-NIPAM, PDMA-NIPAM copolymers and for a conventional polyacrylamide in solution at 5 g / 100 ml in water.

Figures 2: Evolution of the viscosity as a function of the temperature of copolymers according to the invention

- the PAM-NIPAM T10 copolymer, in water, in a 0.2M K2CO3 buffer and a 50 mM Tris-Taps, 7M urea buffer which can be used for DNA sequencing (FIG. 2a) and

- a PAM-NIPAM copolymer at two different concentrations (2 and 3 g / 100ml) (Figure 2b).

Figures 3: Example of separation of duplex DNA fragments in the size range 100-12000 base pairs ("kb ladder", Life Technologies, Paisley, UK) in a separation medium according to the invention based on a PAM-NIPAM polymer (T15) in solution at 2 g / 100ml in TRIS-TAPS buffer at 25 ° C (Figure 3a) and 60 ° C (Figure 3b).

Figures 4: Electropherograms representing the separation of restriction fragments "PhiX-174-RF DNA Hae III digest" (Pharmacia biotech) in a medium according to the invention obtained based on polymer T7, at 20 ° C (Figure 4a) and at 50 ° C (Figure 4b). Figures 5: Example of separation of duplex DNA fragments (100 bp fluorescein ruler, Bio-Rad) in a separation medium according to the invention based on T21 at two temperatures 20 ° C (Figure 5a) and 60 ° C ( Figure 5b).

Figures 6: Portions of electropherograms representing the separation of a sequence reaction product obtained with a medium according to the invention based on a PAM-NIPAM (T10) copolymer at 5 g / 100 ml in TRIS-TAPS 7M urea buffer at 60 ° C (Figure 6c), PAM-NIPAM (T10) at 3 g / 100ml (Figure 6b) and with a commercial sequencing medium (POP6 Perkin-Elmer) (Figure 6a).

Figures 7: Portions of electropherograms representing the separation of a sequence reaction product obtained with a medium according to the invention based on a PAM-NIPAM (T10) copolymer at 5 g / 100 ml in TRIS-TAPS 7M urea buffer at 60 ° C (Figure 7c), PAM-NIPAM (T10) at 3 g / 100ml (Figure 7b) and with a commercial sequencing medium (POP6 Perkin-Elmer) (Figure 7a).

Figure 8: Electrophoregrams representing the separation of large duplex DNA "high Mw markers" (Life Technologies, Paisley, GB), by electrophoresis drawn from a medium according to the invention obtained based on polymer T10 at 60 ° C.

Figures 9: Evolution of viscosity as a function of temperature for

- a PVA-NIPAM copolymer, compared to that of a PVA polymer and

- a POP-POE-POP copolymer compared to that of a POE polymer at a concentration of 5 g / 100 ml.

Figures 10: Example of separation of duplex DNA fragments in the size range 50-500 base pairs (sizer 50-500 bp, Pharmacia biotech) in a separation medium according to the invention based on PVA-NIPAM at two temperatures 20 ° C (Figure 10a) and 40 ° C (Figure 10b).

Figures 11: Electropherograms representing the separation of the sizer 50-500 bp, Pharmacia biotech, obtained with in a medium based on POE (Figure 11a), based on POP-POE-POP at 25 ° C (Figure 11 b) and at POP-POE-POP base at 45 ° C (Figure 11 c).

Figure 12: Bandwidths for a series of separations of single-stranded DNA fragments in denaturing medium (fluorescein 50 bp ladder,

Pharmacia Biotech), in media according to the invention differentiated by the average number and the average length of the segments with LCST: smaller bandwidths correspond to better separation.

EXAMPLE 1:

Preparation of an LCST macromonomer of non-functionalized pNIPAM with a molecular weight close to 10,000 for the preparation of thermogelling copolymer in accordance with the invention.

1) Polymerization of NIPAM

The radical polymerization of NIPAM is carried out in pure water, at a temperature slightly above ambient but below

LCST of the polymer. The initiator is a redox couple whose oxidant is potassium persulfate, K ₂ S ₂ O ₈ (KPS) and the reducing agent is aminoethanethiol

AET, HCI. The priming reaction is:

K ₂ S ₂ O ₈ + 2CI ^" , NH ₃ ⁺ -CH ₂ CH ₂ -SH → 2KHSO ₄ + 2CI \ HN ₃ ⁺ -CH ₂ - CH ₂ -S ^*

The AET.HCI also acts as a transfer agent, which makes it possible to control the length of the chains.

Procedure

20 g of NIPAM (0.18 mole) and 200 ml are introduced into a 500 ml three-necked flask surmounted by a condenser and equipped with a nitrogen inlet device. of water, the mixture is then stirred and heated to 29 ° C by a water bath. The nitrogen bubbling is started. After 45 minutes, 0.42 g of AET, HCl (0.0037 mole) previously dissolved in 20 ml of water is added, then 0.0018 moles of potassium persulfate (KPS) dissolved in a minimum amount of 'water. The mixture is kept under stirring for 3 hours. The solution is then concentrated and then lyophilized.

To isolate the polymer, precipitation is carried out according to the following procedure:

The solid obtained is redissolved in 100 ml of methanol. the hydrochloride present is neutralized by adding 0.0037 mole of KOH (ie 0.208 g dissolved in about 25 ml of methanol) incorporated dropwise into the solution. The salt formed, KCI, precipitates and is extracted by fiitration. The filtrate thus recovered is concentrated and then poured dropwise into 4 liters of ether. The polymer precipitates and is recovered by fiitration on a No. 4 frit. The solid is then dried under vacuum of a vane pump. The mass yield is of the order of 50%.

The above protocol leads to an amino polymer "PNIPAM-A-10", and corresponds to initiator-monomer ratios Ro = 0.02 and Ao = 0.01, where: Ro = [R-SH] / [NIPAM ] and Ao = [KPS] / [NIPAM].

Different other amino polymers were prepared according to the same protocol by varying the polymerization temperature and the Ro ratio, while retaining an Ao ratio of 0.01. These polymers are described and defined in Table 1. 2) Modification of the amino PNIPAM with a view to its copolymerization with one or more soluble segments at temperatures T1 and T2.

The PNIPAM macromolecules synthesized have amino functions at the end of the chains, these originating from the aminoethanethiol initiator AET.HCI. By reaction of the amino function on acrylic acid, a vinyl double bond is fixed at the end of the chain according to the following reaction scheme:

PNIPAM— NH ₂ + CH = CH ₂

Procedure:

50 ml of methylene chloride, 1.5 g of acrylic acid (0.021 mole), 9 g of PNIPAM and 4.3 g of dicyclohexylcarbodiimide (DCCP) (0.21 mole) are introduced into a 100 ml beaker. The reaction medium is stirred for one hour. The acrylic acid being in strong excess compared to PNIPAM (the quantity of acrylic acid is approximately twenty times that of PNIPAM), it can be assumed that all the amino functions have been modified, which will be confirmed by the copolymerizations described in l 'example 2. The mixture is then filtered on a No. 4 frit to remove the dicyclohexylurea precipitate, a by-product resulting from the transformation of DCCI.

The mixture is then concentrated to 15 ml and then poured dropwise into 200 ml of ether to precipitate the polymer. It is filtered on a No. 4 frit and the solid is washed with three times 100 ml of ether and then it is dried under vacuum with the vane pump overnight.

A poly- (NIPAM) macromonomer is thus obtained carrying an allyl function at the end of the chain, with a mass yield of the order of 70%.

The molar masses of the macromonomers thus prepared were measured by SEC (size exclusion chromatography) under the following conditions: a: in 0.5 M aqueous LiNO ₃ solution at 20 ° C using 4 Shodex OH Pack B803 to B806 25 cm columns in series, with refractometric detection and calibration of molecular weights relative to a POE standard b: in THF at 40 ° C, with ultrastyragel column, double refractometric detection and universal calibration against polystyrene samples. This second method of determination is more certain; because on the one hand the universal calibration overcomes the difference in flexibility between the chains of the polymer to be studied and standards, and on the other hand because THF is a better solvent for PNIPAM than water.

TABLE 1

These results show that it is possible to vary the average molecular weight of the macromonomers by varying the polymerization temperature, and the initiator / polymer ratio Ro, the highest Ro ratios leading to the lowest molecular weights. They also show that the macromonomers' polymolecularities are high, generally greater than 2.

EXAMPLE 2:

Preparation of various copolymers with comb structure and comprising, as LCST segments, the PNIPAMs prepared in Example 1.

The subject of this example is the preparation of copolymers according to the invention by copolymerization of PNIPAM macromonomer (s) obtained according to Example 1 with monomers of the water-soluble type. a) Synthesis This copolymerization is carried out in water at room temperature. The initiator used is the redox couple ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ) [20 g / 1] - sodium metabisulfite (Na ₂ S ₂ O ₅ ) All of the copolymers thus prepared are purified by precipitation in acetone, with the exception of the T7 copolymer, the soluble segments of which consist of dimethylacrylamide DMAM, which is purified by ultrafiltration and lyophilization.

The various polymers synthesized are listed in Table 2 below, which also reports on the quantities of reagent used (indicated in parenthesis).

In the picture :

- The viscosities are expressed in centipoise [TO BE EXPRESSED IN

SI], for a polymer in solution at 5 g / 100 ml in water and at a shear rate of 10 s ⁻¹ , using a cone-plane viscometer with a uniform shear rate Brookfield LDV III;

- They were measured in aqueous 0.5 M LiNO ₃ solution at 20 ° C using 4 Shodex OH Pack B803 to B806 columns of 25 cm in series, with refractometric detection. They are expressed in 10 ⁶ g / mole. The values in brackets are the values in "POE equivalent" (obtained by comparison with polyoxyethylene standards), with refractometric detection. The T10 copolymer as well as other copolymers of the same family not described here were also analyzed by molecular mass using detection by multi-angle laser light scattering ("MiniDawn Wyatt), which makes it possible to obtain the mass In comparison with the masses in "POE equivalent" of the same polymers, it has been evaluated that for all of the polymers presented in table 2, the absolute molecular mass is of the order of twice the mass in POE equivalent : this estimated value is given in bold in the table.

Knowing the average molecular weight of the copolymers, that of the LCST or macromonomer segments, and the mass fraction of LCST segments incorporated into the copolymer, the average number of LCST segment per polymer (mass averages), denoted Ns, is easily deduced in Table 2, using the formula:

Ns = f Mw (copolymer) / Mw (macromonomer)

- The values in bold represent the fraction f of LCST segments in the final copolymer (fraction by mass).

All the copolymers described in Table 2 have a thermo-viscosifying character.

TABLE 2

00 o

The procedure presented below is given for the preparation of the T7 copolymer. The procedures for the other copolymers can be deduced therefrom by modifying the nature and the concentration of the reactants, and optionally the reaction temperature in accordance with Table 2.

PNIPAM-10 and the monomer under consideration are introduced into a 100 ml flask as well as 30 ml of distilled water. This mixture is stirred for two hours at room temperature with nitrogen bubbling in order to remove the dissolved oxygen. The mixture is then brought to the temperature chosen for the polymerization using a thermostated bath, then the initiators are added in the form of a solution of (NH ₄ ) ₂ SO ₈ at 20 g / 1 and of a solution of Na ₂ S ₂ O ₅ to 5 g: L, ie respectively 0.1% and 0.03% by mole of the amount of monomers introduced. The mixture is kept under stirring and bubbling for 4 hours. Before the introduction of the initiators, then every hour during the polymerization, samples of the reaction medium are taken (0.1 ml diluted in 5 ml of methanol) in order to follow the progress of the reaction by steric exclusion chromatography.

Generally, the data associated with the visual observation of the increase in the viscosity of the reaction medium makes it possible to conclude that the reaction is progressing well, with an almost total yield, b) Purification

The purification of polymers is done differently depending on the nature of the skeleton. For polymers whose backbone consists of DMAM, ultrafiltration was used according to the following procedure:

The reaction medium is diluted in one liter of water and then ultrafiltered through a membrane, the cut-off threshold of which is 100,000 Daltons. The polymer solution is then concentrated and then lyophilized. The yield is quite variable, generally around 60%.

The macromolecules with an acrylamide skeleton are precipitated in acetone according to the following procedure: The reaction medium is slowly precipitated from 1 liter of acetone then filtered through a No. 4 frit and washed with three times 100 ml of acetone. The solid is recovered and then dried overnight with a vane pump.

The mass yield is much better than for ultrafiltration-lyophilization and is close to 90%.

The incorporation rate of the macromonomers was checked by NMR of hydrogen on the polymers diluted to 2g / 100ml in heavy water (Bruker apparatus at 250 and 400 MHz). It is found that the rate of incorporation depends, apart from the experimental fluctuations, only on the ratio between the initial mass of PNIPAM and the initial mass of hydrophilic monomer. It is, respectively, 6.5 +/- 0.3 mol%, for an initial concentration of 0.4 g of PNIPAM for 2.8 g of acrylamide, and 12 +/- 1 mol%, for a initial concentration of 0.8 g of PNIPAM per 2.8 g of acrylamide.

EXAMPLE 3:

Evaluation of the rheological behavior of DMAM / PNIPAM and AM / PNIPAM copolymers prepared according to Example 2 as a function of the temperature.

In this example, each of the copolymers was introduced at a rate of 5 g / 100 ml in purified water (MilliQ). The viscosity of each of the corresponding solutions was measured on a cone-plan Brookfield DV3 rheometer controlled by Rheocalc software (Sodexim, Muizon, F). The retained shear rate is 10 (1 / s) for a temperature gradient of 1 ° C per minute. The results obtained are shown in Figure 1.

It can be seen that the various synthesized copolymers indeed exhibit the rheological properties which make it possible to use them according to the invention, and in particular, that they have a viscosity V2 at a temperature T2 significantly higher, by a factor greater than 2 (100 %), often of order 10, and possibly up to a factor of 60, at the viscosity V1 obtained at a temperature T1 lower than T2 by at least 20 °. For the polymers described in this example, the temperature T1 may be between 20 and 40 ° C, or even lower, and the temperature T2 may be greater than 45 °, and preferably of the order of 60 ° C.

It is also noted that the polymer T10AA, prepared as a control according to the same protocol but without the PNIPAM macromonomer, and therefore being unable to exhibit in its structure the multiplicity of LCST blocks which characterizes the copolymers according to the invention, has a decreasing viscosity weakly and continuously as a function of the temperature, and therefore cannot exert the beneficial effects of the invention. Furthermore, for all of the copolymers and at a temperature change rate of 1 ° C. per minute, no significant hysteresis is observed, the viscosity curve being essentially identical as the temperature rises and falls.

By comparing FIG. 1 and Table 2, it is noted that the viscosity at low temperature is strongly correlated with the molecular weight of the copolymer. We also note that the thermoviscosifying behavior and the increase in viscosity with temperature are strongly correlated with the average number of LCST segments per Ns chain, the highest values of this parameter corresponding to the strongest thermoviscosifying effects. Figure 2a illustrates the rheological behavior of the copolymer

T10 in an ionic electrolyte such as for example potassium carbonate, or a buffer of the TRIS-TAPS 50 mM / Urea 7M type as used for sequencing.

In FIG. 2b are shown the behaviors of two solutions based on the PAM-NIPAM T10 copolymer, one for a concentration of 3 g / 100 ml of copolymer and the other for a concentration of 2 g / 100 ml of copolymer. We note that the thermo-thickening character is sensitive from 2 g / 100ml, but reinforced to 3 g / 100ml and even more to 5 g / 100ml (figure 1), the concentration being also a parameter that will usefully be varied to adapt the media. according to the invention according to the particular applications.

In particular, most of the polymers presented in Table 2 have a thermo-viscosifying character for concentrations less than or equal to 5 g / 100 ml, that is to say that they do not exhibit hysteresis. significant of their viscosity in temperature rise and fall, and are capable of flow in less than 30 s when the container is inverted.

The T16 polymer, on the other hand, gives rise to a gel-like state at 60 ° C. for concentrations of 8 g / 100 ml and more.

EXAMPLES 4:

Separation properties of separation media for capillary electrophoresis comprising, as copolymer, one of the copolymers prepared according to Example 2.

The electrophoresis experiments presented in this and the following examples were performed using a laboratory-built apparatus, similar to that described in Lindberg et al., Electrophoresis, 18, 1973 (1997). The separated DNAs are detected by fluorescence with excitation by an Argon laser at 488 nm and emission at 530 +/- 30 nm. The injection is of the electrokinetic type. The capillary, made of fused silica covered with polyimide (polymicro), with an internal diameter of 100 μm, is thermostatically controlled between the injection point and the detection point by circulation of silicone oil in a sealed envelope, with the exception of the first 2 and the last 2 centimeters. (unless otherwise stated, this type of capillary will be used in the electrophoresis experiments presented below)

Trial 4-1

Separating properties of a medium comprising, as a copolymer, the PAM-NIPAM copolymer (T15) at a concentration of 2 g / 100 ml The medium is mixed with the TRIS-TAPS buffer (50 mM) and with the DNA marker (for SYBR GREEN I 10 ^"4 ).

In this particular case, the capillary is filled at 25 ° C, the injection is carried out in 10 seconds at 25 volts per centimeter and the sample to be separated is of the same nature as that of the previous test. The separating properties of said medium are evaluated at two temperatures 25 ° C and 60 ° C and Figures 3a and 3b show these properties. It is found that the separation is both more resolving and faster at 60 ° C.

Trial 4-2

Separating properties of a separation medium based on the PAM-NIPAM copolymer (T12).

The medium is introduced into the capillary at 25 ° C. at a concentration of 8 g / 100 ml mixed with the TRIS TAPS buffer (50 mM) and the DNA marker SYBR GREEN I (Molecular probes) diluted at 10 ^"4 relative to to the stock solution sold by the supplier. We note a similar behavior with an improvement of the resolution and the separation time, when the temperature chosen for the separation is 60 ° C. We also note that the resolution for large fragments of Duplex DNA is better with the T15 copolymer, prepared with a low level of transfer agent and therefore having a high molecular weight, than with the T12 copolymer prepared with a higher rate of transfer agent and having a lower molecular weight .

Trial 4-3

Separating properties of a medium comprising, as copolymer, the PDMAM-NIPAM copolymer (T7) at a concentration of 2 g / 100 ml. This medium is mixed with the TRIS-acetate buffer (50 mM) and with the 10 ^"4 SYBR GREEN I DNA marker.

In this particular case, the sample is the marker "Phi-X 174-

RF DNA, Hae III digest "(Pharmacia biotech), whose fragments have sizes between 72 and 1358 bp, the injection is carried out in 5 seconds at 20 volts per centimeter and the sample to be separated is of the same nature as that from the previous test.

The separating properties of said medium are evaluated at two temperatures 25 ° C and 50 ° C and Figures 4a and 4b show these properties. It is noted, as in the previous test, that the separation is both more resolving and faster at higher temperature.

Test 4-4 Separating properties of a medium comprising, as copolymer, the PAM-NIPAM T21 copolymer, prepared from the macromonomer PNIPAM-20, at a concentration of 2 g / 100 ml.

The medium is mixed with the TRIS-acetate buffer (50 mM). For this separation medium, the viscosity at high temperature is relatively low, and does not allow total suppression of the electroosmosis. Consequently, the capillary was prior to its use, washed with a 1 M hydrochloric acid solution comprising 1 g / 100 ml of polyvinylpirolidone of molecular mass 1,000,000 (Polysciences, Eppelheim, D). In this particular case, the sample is the "100 bp fluorescein ladder" marker, Bio-Rad, the fragments of which have sizes between 100 and 1000 bp, the injection is carried out in 10 seconds at 25 volts per centimeter.

The separating properties of said medium, introduced into the capillary at 25 ° C, are evaluated at two temperatures 25 ° C and 50 ° C and Figures 5a and 5b show these properties.

It is noted, as in the previous test, that the separation is faster at higher temperature, but that the gain in resolution is less significant than for example T15 or T7, which have a more marked thermo-thickening character. This confirms that the thermo-thickening character, as it appears in the viscosity curves as a function of the temperature, is a characteristic advantage of the media according to the invention, and that the said viscosity curves can be used as a guide for optimization. separation properties.

Trial 4-5

Separation of block products using a separation medium comprising the PAM-NIPAM copolymer (T10). The copolymer is used at two different concentrations, 3 g / 100ml and 5 g / 100ml, respectively, in TRIS TAPS buffer (50 mM), 7M urea. The pH of the medium is of the order of 8.2. As a control, a test is carried out with a commercial sequencing medium (POP6 Perkin-Elmer), used as received.

The capillary used has a length of 40 cm with an effective length of 30 cm and an internal diameter of 100 μm. For separation media based on T10 polymer, which do not have specific adsorption properties on silica, the capillary is prior to its use, washed with a 1 M hydrochloric acid solution and comprising 1 g / 100 ml of polyvinyllpirolidone.de molecular weight 1,000,000. The separation medium is introduced into the capillary at 25 ° C.

The test sample is the product of a DNA sequence reaction ssM13mp18, ("T-terminated fragments"), prepared by cyclic sequencing ("cycle sequencing") with the fluorescein-primer kit distributed by Amersham, as indicated. supplied by the manufacturer.

The electric field is 200 volts per centimeter and the injection is carried out in 8 seconds at 200 volts per centimeter. The separating capacities of each of these media are evaluated at a temperature of 60 ° C. Figures 6 and 7 show respectively the separating capacities of the commercial sequencing medium (control figure a), and media according to the invention based on the T10 copolymer at respective concentrations of 3 g / 100ml (Figures b) and 5 g / 100ml (figures c) (the numbers above the peaks represent the length of the DNA fragment minus 48 bases)

Trial 4-6

Separator properties with respect to sequence fragments using different separation media in accordance with the invention.

The media tested are based on either the PAM-NIPAM copolymer (T12) at a concentration of 8 g / 100ml, the PAM-NIPAM copolymer (T13) with a concentration of 5 g / 100ml or the DMAM-NIPAM copolymer (T7) with a concentration at 5 g / 100ml, respectively. Each of these media is of course supplemented with TRIS TAPS buffer (50 mM) and 7M urea. They have a pH of 8.2, the nature of the sample and the separation conditions are the same as those used in the previous test. These various tests confirm that several media according to the invention, having a relatively moderate viscosity at ambient temperature, of the order of 1000 mPa m ^"1 s ^{" 1} or even significantly lower, make it possible to separate DNA sequence fragments with performance equal to or better than in trade circles. It will be noted in particular that the resolution obtained with T10 at 5g / 100ml is much higher than that obtained with POP6, in a slightly lower time.

Trial 4-7

Separation using DNA fragments of a medium comprising, as copolymer, the PAM-NIPAM (T10) copolymer.

The copolymer used at a concentration of 2 g / 100 ml is mixed with the TRIS-TAPS buffer (50 mM), 2 mM EDTA and the DNA marker

SYBR GREEN I 10. The length of the capillary is 15 cm, including 10 cm to the detector, and the capillary is of the "DB17" (JW scientific) type with an internal diameter of 100 micrometers, in order to suppress the residual electroosmosis appearing with this medium.

In this particular case, the sample is the High molecular weight standard marker (Life Technologies), and has fragments between 8271 and 48502 base pairs, the injection is carried out in 5 seconds at 100 volts per centimeter. The separation is carried out in pulsed fields with square pulses of +/- 200V, an asymmetry between the pulses + and - of 20% and a frequency of 30 Hz. The separation of the fragments can be carried out in less than 20 min (Figure 8), against several hours in an ordinary entangled polymer solution (Heller et al. Electrophoresis, 16, 1423-1428 (1995).

Trial 4-8

Separation properties and resolution at 40 ° C. of separation media in accordance with the invention. The media tested contain polymers based on NIPAM macromonomers of different length (T22, T26, T24 and T25, respectively), dissolved at 3 g / 100ml in TRIS TAPS buffer (50 mM), 7M urea.

The pH of the medium is of the order of 8.2. the sample used is a "50 BP LADDER- fluorescein Pharmacia.

The results in terms of peak width are given in FIG. 12.

It appears that the best resolution (smaller peak width) is for this series obtained with the polymer T24 (prepared from macromonomers of average molecular mass 15000), and that the media based on T25 and T26 also give very satisfactory and sufficient results to perform good quality sequencing.

Test 4-9 Separation of sequence reaction products using a separation medium according to the invention at constant temperature.

The medium tested is of the T16 type, at 5 g / 100 ml, in 50 mM Na TAPS buffer, 2 mM EDTA, 7M urea, the said medium being introduced into the capillary at 50 ° C, and the separation also taking place at 50 ° vs. We use an ABI 310 device.

It is noted that the reading is carried out very well up to more than 500 bases, and that the introduction at low temperature is not in this precise case essential for the implementation of the medium according to the invention. This advantageous property comes from the fact that the medium is of the thermo-viscous type, and therefore does not present at the temperature at which the separation takes place, a gel type state which would prevent its introduction into the capillary.

EXAMPLE 5:

Preparation of PVA-NIPAM copolymers (PolyVinylAlcohol / Poly-N- Isopropylacrylamide).

The polyvinyl alcohol constituting the water-soluble backbone of the copolymer is obtained beforehand by hydrolysis of polyvinyl acetate. The polymer used for the study has an acetate level of 12.4% by mole and a molar mass by weight of 145,000 g / mole. Its intrinsic viscosity in water at 30 ° C is 92 ml / g, the critical concentration for covering the C * chains is approximately 1.25 g / 100ml. The synthetic route followed is of the "grafting from" type. It is described by Nonaka & al. in a homogeneous medium (Y. Nonaka, Y. Ogata, S. Kurihara, Journal of Applied Polymer Science, vol. 52, 951-957 (1994)) or Ikada & al. in the case of a polymethyl methacrylate skeleton (Y. Ikada, Y. Nischizaki, I. Sakwada, J. Polym. Sci., Vol. 12, 1829-1839 (1974)). The synthesis is carried out at 60 ° C. for 20 hours in dimethyl sulfoxide (DMSO), in the presence of potassium persulfate (KPS) in order to generate radicals on the PVA skeletons. These radicals then induce the polymerization of the monomer present in the medium to lead to the final product. The formation of carbonyl groups according to a secondary reaction of keto-enolic tautomerism causes the appearance of a yellow coloration effectively observed during the synthesis.

Table 3 below shows the characteristics of PVA-NIPAM obtained according to this protocol.

TABLE 3

determined by SEC in THF at 40 ° C, with ustrastyragel column (Waters 150 CV + chromatograph), refractometric detection and simple calibration against polystyrene standards. ^c determined by NMR.

EXAMPLE 6

Preparation of a linear triblock POP-POE-POP copolymer

This copolymer is prepared according to a protocol derived from that described by J.P. Kaczmarski and J.E. Glass, Langmuir, 1994, 10, 3035-3042.

About 10 g of polyethylene glycol with a molecular weight of 35,000 (Merck, Hohenbrunn, D) (PEG) and 100 ml of anhydrous toluene are mixed under an argon atmosphere (low molecular weight polyoxyethylenes are commonly called "polyethylene glycol"). Once the PEG is dissolved in toluene, the mixture is heated to reflux under argon and approximately 10 to 15 ml of anhydrous toluene are evaporated. The solution is cooled to room temperature and 120 mg (0.2% by weight) of dibutyltin dilaurate are added to the solution. A stoichiometric amount of isophorone diisocyanate (128 mg) is dissolved in 5 ml of anhydrous toluene and added to the mixture. The reaction is followed by spectroscopy visualization

-1 infrared (by enhancing the reduction in the isocyanate band to 2260 cm). After 90 minutes, 2.4 g of polypropylene glycol monobutyl ether (Mn 400) (PPG) (Aldrich, Milwaukee, USA) are dissolved in 20 ml of anhydrous toluene and added dropwise to the mixture (low molecular weight polyoxypropylenes are commonly called "polypropylene glycol"). The reaction is continued overnight (approximately 15 hours) at 5 ° C. (the isocyanate band decreases from the start of the reaction and then stabilizes). 80 ml of toluene are added to the mixture in order to reduce the viscosity of the solution and the polymer is precipitated using 550 ml of petroleum ether, filtered through sintered glass No. 4, washed with an excess of ether of petroleum and vacuum dried.

EXAMPLE 7:

Determination of the heat-thickening behavior of a PVA-NIPAM copolymer and a linear POP-POE-POP triblock copolymer.

The rheometer used in this example is identical to that used in Example 3 above. The PVA-NIPAM used corresponds to that of Table 3 and the linear triblock copolymer POP-POE-POP is that prepared in Example 6. In Figure 9 are shown the rheological behaviors of media comprising

- respectively 4.5% by weight of PVA-NIPAM or 4.75% by weight of PVA dissolved in a 50 mM TRIS-TAPS electrolyte (Figure 9a). It is noted that the PVA-NIPAM copolymer exhibits a heat-thickening character from a temperature above 35 ° C., which PVA does not have alone, and

- the heat-crosslinking nature of the linear triblock POP-POE-POP copolymer which thickens rapidly beyond a temperature of 20 ° C (figure 9b). Also shown on this graph is the rheological behavior of the polyethylene glycol polymer at the same concentration. In this case there is no increase in viscosity as a function of temperature.

EXAMPLE 8:

Separation properties of an electrophoretic separation medium comprising a PVA-NIPAM copolymer according to Example 5.

The fluorescence detection is carried out under the same conditions as those described in Example 4. As regards the capillary channel, it has a total length of 40 cm and an effective length of 30 cm, an internal diameter of 100 μm and it is coated with an acrylamide derivative according to the method described in by HJERTEN J. Chromatogr., 1985, 347, 191 in order to suppress electroosmosis.

The electrolyte comprises 4.75 g / 100 ml of the PVA-PNIPAM copolymer and 50 nM of TRIS TAPS buffer.

The electric field is 200 volts per centimeter. The injection is carried out in 10 seconds at 200 volts per centimeter. The sample is the sizer 50-500, Pharmacia Biotech, diluted to 1/500 in MILI Q water (Miliport).

The separating properties are appreciated at two temperatures, 20 ° C (Figure 10a) and 44 ° C (Figure 10b). The separation time is improved, but the resolution is not significantly increased, which is probably due to the too low viscosity reached at 44 ° C for this medium.

EXAMPLE 9 Separating properties of a separation medium comprising, as a copolymer, a POP-POE-POP triblock copolymer according to Example 8.

The medium was tested under the conditions recommended for the medium described in Example 7 above.

The results obtained are represented in FIG. 1 1. FIG. 11 a shows the separating properties of the control medium, that is to say simply based on unmodified polyethylene glycol, with

20 ° C. Figure 1 1b shows the separating properties of a medium comprising the POP-POE-POP copolymer at a temperature of 20 ° C by analogy to the control medium and FIG. 11c illustrates the separating properties of a medium based on said copolymer but at a temperature of 50 ° C. This shows that the copolymer exhibits from room temperature a resolution higher than that obtained with POE alone, undoubtedly because of its higher molecular weight, but that the properties are still greatly improved when we pass at 50 ° C., and shows that polymers of the block type having at least two blocks with LCST can also be advantageously used in the context of the invention for carrying out electrokinetic separations.

EXAMPLE 10:

Preparation of a PAAgNIPAM charged copolymer (Polyacrylic Acid / Poly-N-lsopropylacrylamide).

The polyacrylic acid used is in solution at 12.5 g / 100ml in water. The polymer noted PAA500 has a weight-average molar mass of 500,000 g / mol (Fluka)

The skeleton of the PAA500 is sensitive to pH; the ionizable carboxylic functions have a pKo around 4.25 pH units.

1) Synthesis of the PAAgNIPAM copolymer a) Procedure

The synthetic route followed consists in grafting short chains of NIPAM onto a weak fraction of the carboxylic acid functions of a polyacrylic acid skeleton. It breaks down into two stages:

Synthesis of oligoNIPAM, short chain of PNIPAM (Mw ≈ 2000 g / mol) terminated by an amino function, and this by radical polymerization of NIPAM monomers in methanol in the presence of the transfer agent AET.HCI (2-aminoethanethiol hydrochlorinated) and the initiator AIBN (2,2'-azobistutyronitril) at 60 ° C for 20 hours, (this method of synthesis constitutes an alternative to that, in aqueous solution, used to prepare the polymers PNIPAM-A in the example 1). The oligoNIPAM of known length is then grafted onto the PAA500 skeleton reaction between acid and amino functional groups in the presence of a podiimide initiator:

- either in water at 60 ° C for 1 hour (EDC initiator 1, 2 dichioroethane),

- Either in N-methylpyrrolidone (NMP) at 60 ° C for 24 hours (initiator DCCI dicyclocarbodiimide).

Table 4 shows the composition of the PAAgNIPAM copolymer obtained by this protocol.

Table 4:

a% by weight of NIPAM determined by NMR.

EXAMPLE 11:

Rheological behavior of the PAAgNIPAM copolymer

The evolution of the viscosity as a function of the temperature was plotted under the same conditions as in Example 6 above except for the use of a shear gradient of 100 s and a speed of temperature rise 2 ° C per minute. The heat-thickening effect appears at 33 ° C for PAAgNIPAM I and extends up to 65 ° C, exhibiting over this temperature range only a growth phase and the start of a plateau. This shows that using the examples and descriptions given above, it is also possible to prepare copolymers having a charged hydrophilic skeleton and a multiplicity of blocks with LCST giving rise to thermocrosslinking and usable within the framework of invention.

Claims

1. Thermosensitive medium for the separation of species within a separation channel, said medium comprising an electrolyte in which at least one set of block copolymers is dissolved, characterized in that said block copolymers:

- are present in said electrolyte at a sufficient concentration to give said medium the ability to reverse reversibly from a state of viscosity V1, obtained at a temperature T1, towards a state of viscosity V2 at least 100% higher than V1, obtained at a temperature T2 at least 20 ° C higher than T 1 and

- include in their structure at least

- two non-contiguous polymer segments having an LCST in said electrolyte and having an average number of atoms along their skeleton greater than 50 and - a polymer segment soluble in the electrolyte at temperatures T1 and T2.

2. Medium according to claim 1 characterized in that the temperature T1 is between 15 ° and 30 ° C.

3. Medium according to claim 1 or 2 characterized in that the temperature T2 is between 40 ° C and 80 ° C.

4. Medium according to one of claims 1 to 3 characterized in that the viscosity V2 is greater by at least a factor equal to 5 than the viscosity

V1.

5. Medium according to one of claims 1 to 4 characterized in that the LCST of a significant fraction of said LCST segments is between T1 and T2.

6. Medium according to one of the preceding claims, characterized in that all of the LCST segments represent between 2% and 25% and preferably between 5 and 15% of the average total molar mass of the copolymers.

7. Medium according to one of the preceding claims, characterized in that all or part of the blocks with LCST have along their skeleton an average number of atoms greater than 75, or an average molecular mass greater than 2,500.

8. Medium according to one of claims 1 to 7 characterized in that all or part of said polymers are in the form of linear block polymers.

9 Medium according to one of claims 1 to 7 characterized in that all or part of said polymers are in the form of comb copolymers whose backbone is formed by one or more segments soluble in the electrolyte at temperatures T1 and T2.

10. Medium according to one of the preceding claims, characterized in that all or part of the copolymers have an average number of LCST segments per chain greater than 2 and preferably greater than 5.

11. Medium according to one of the preceding claims, characterized in that all or part of the copolymers has a molecular mass greater than 30,000 or a number of atoms along the main skeleton greater than 2,000.

12 Medium according to one of the preceding claims, characterized in that all or part of the copolymers has a molecular mass of between 50,000 and 3,000,000 or a number of atoms along the main skeleton of between 2,500 and 100,000.

13. Medium according to one of the preceding claims, characterized in that all or part of the copolymers has an average number of atoms along a section of soluble segment, between two consecutive connecting points of said soluble segment with segments at LCST, higher than 210.

14. Medium according to one of the preceding claims, characterized in that all or part of said LCST polymer segments are derived from one or more polymers chosen from: - polyvinylalkyl ether,

- hydroxyalkyicelluloses,

- homopolymers of etheroxides,

- random and block copolymers of etheroxides, - alkylene homo- and co-polymers, and

- polyacrylic derivatives derived from the homopolymerization or co-polymerization of monomers chosen from acrylic and methacrylic acids, alkyl acrylates and methacrylates, N-alkyl-acrylamides or -methacrylamides, N'N- dialkyl -acrylamides or - methacylamides, arylacrylamides or -methacrylamides and alkylarylacrylamides or -methacrylamides.

15. Medium according to one of the preceding claims, characterized in that the polymeric segment or segments soluble at temperatures T1 and T2 consist of at least one polymer chosen from polyethers, polyesters, homopolymers and random statistical copolymers of the polyoxyalkylene type, polysaccharides, polyvinyl alcohol, polyvinylpirrolidone polyurethanes, polyamides, polysulfonamides, polysulfoxides, polystyrenesulfonate, polyacrylamides. and substituted or insoluble polymethacrylamides in said electrolyte.

16. Medium according to one of the preceding claims, characterized in that the copolymer is chosen from:

- copolymers of the comb copolymer type, the backbone of which is of the acrylamide, acrylic acid, acryloylaminoethanol or dimethylacrylamide type and at the level of which are lateral segments of the poly (N-alkyl or N, N dialkyl) acrylamide type, of the polyoxypropylene type or polyoxyethylene / propylene copolymer, random or block, or of polyether type and

- copolymers of the block copolymer type and having, along their backbone, alternating segments of polyoxyethylene type and segments of polyoxypropylene type, or alternating segments of polyoxyethylene type and segments of polyoxybutylene type or alternating segments of polyethylene and polyether type segments more hydrophobic than polyoxyethylene.

17. Medium according to one of the preceding claims, characterized in that the copolymer is chosen from polyacrylamide / poly (N-isopropylacrylamide) (PAM-NIPAM); polyvinyl alcohol / poly (N-isopropylacrylamide) (PVA-NIPAM), polyoxyethylene / polyoxypropylene, polyacrylamide / oxyethylene- oxypropylene copolymer, polyacrylamide / polyoxypropylene, polyacrylic acid / polyoxypropylene, polyacrylic acid / oxyethylene-oxypropylene copolymer, polyacrylic acid / poly (N-isopropylacrylamide) and polydimethylacrylamide) -NIPAM).

18. Medium according to one of the preceding claims, characterized in that it transits with a viscosity V1 of between 50 and 1000 mPa m ^"1 s ^{" 1} (SI unit) at a temperature T1 of between 15 and 30 ° C a viscosity V2 greater than V1 by a factor of between 2 and 50 at a temperature T2 of the order of 40 ° C or higher and in that it comprises between 5 g / 100ml and 20 g / 100ml of copolymers having

- an average molecular weight of between 30,000 and

2,000,000 or a number of atoms along the main skeleton (is between 1,000 and 60,000, - a mass fraction of LCST segments between 2% and

20%, and

- an average molecular weight of the LCST segments between 2,000 and 20,000 or an average number of atoms along an LCST segment between 35 and 350.

19. Medium according to one of claims 1 to 17 characterized in that it transits with a viscosity V1 between 100 and 10,000 mPa m ^"1 s ^{" 1} at a temperature T1 between 15 and 30 ° towards a viscosity V2 greater than V1 by a factor between 2 and 100 at a temperature T2 of the order of 40 ° C or higher and in that it comprises between 1 g / 100ml and 8 g / 100ml of copolymers having

- an average molecular weight of between 500,000 and

3,000,000 or a number of atoms along the main skeleton of between 7,000 and 90,000,

- a mass fraction of LCST segments between 2.5% and 15%, and

- an average molecular weight of LCST segments between 4,000 and 30,000 or an average number of atoms along an LCST segment between 60 and 600.

20. Medium according to one of claims 1 to 17 characterized in that it transits with a viscosity V1 between 100 and 10,000 mPa m ^"1 s ^{" 1} (SI unit) at a temperature T1 between 15 and 30 ° C towards a viscosity V2 greater than V1 by a factor between 2 and 100 at a temperature T2 of the order of 40 ° C or higher and in that it comprises between 0.1 g / 100ml and 5 g / 100ml of copolymers having

- an average molecular mass greater than 500,000 or a number of atoms along the main skeleton greater than 7,000,

- a mass fraction of LCST segments between 2% and 15%, and

- an average molecular weight of the LCST segments greater than 4,000 or an average number of atoms along an LCST segment greater than 90.

21. Medium according to one of the preceding claims, characterized in that said copolymer is present in said medium and the concentration of copolymer is less than 20 g / 100 ml, and preferably between 0.1 g / 100 ml and 8 g / 100 ml .

22. Medium according to one of the preceding claims, characterized in that it also comprises adjuvants of the particle type, water-soluble polymers, non-heat-thickening associative polymers, or even neutral or ionic surfactants.

23. Use of a medium according to one of the preceding claims for the separation or analysis of species chosen from molecular or macromolecular species, and in particular biological macromolecules such as nucleic acids (DNA, RNA, oligonucleotides), nucleic acid analogs obtained by synthesis or chemical modification, proteins, polypeptides, glycopeptides and polysaccharides, organic molecules, synthetic macromolecules or particles such as mineral particles, latex, cells or organelles.

24. Use of a medium according to one of claims 1 to 22 for DNA sequencing.

25. Use according to claim 24 characterized in that to separate molecules with a molecular mass of less than 50,000 or oligonucleotides comprising less than 100 nucleotides, or even native or denatured proteins, a medium according to claim 18 is used.

26. Use according to claim 24 or 25 characterized in that for separating for separating DNA sequence reaction products, duplex DNA of less than 1000 base pairs, denatured proteins or synthetic or natural polymers of molecular mass between 20,000 and 1,000,000, a medium according to claim 19 is used.

27. Use according to claim 24 characterized in that to separate duplex DNAs of size between 500 bases and several million base pairs, or particles such as latex, whole cells, whole chromosomes or oganelles, one uses a medium according to claim 20.

28. Use according to one of claims 24 to 27, characterized in that it comprises the following stages:

- the selection of said separation medium according to the characteristics of the species to be separated;

the introduction of this medium into a separation channel of an electrophoresis apparatus in an amount sufficient to constitute the separation medium, said separation channel being maintained at a temperature close to the temperature T1;

- bringing a significant portion of the channel to temperature T2 either before or after the introduction of a sample; - the introduction at the inlet of the separation channel of a quantity of sample;

- carrying out the separation at a temperature of the order of T2 in the portion of the thermostatically controlled channel and

- detecting the migration of the analytes initially contained in the sample.

29. Use of a medium according to one of claims 1 to 23 in an automated electrophoresis apparatus.

30. Use of a medium according to one of claims 1 to 23 within a microfluidic system.

31. A capillary electrophoresis device comprising, as separation medium, a medium according to one of claims 1 to 23.