WO2024219965A1

WO2024219965A1 - Polyelectrolyte complex

Info

Publication number: WO2024219965A1
Application number: PCT/NL2024/050198
Authority: WO
Inventors: Evelien MAASKANT; Willem VOGELZANG; Shanmugam THIYAGARAJAN; Julian Johannes ENGELHARDT; Evert Cornelis SIMONSZ; Louis Cornelia Patrick Maria De Smet; Wouter POST; Arijana SUŠA; Jasper VAN DER GUCHT; Johannes Teunis Zuilhof; Jacobus Van Haveren
Original assignee: Stichting Wageningen Research; Wageningen Universiteit
Priority date: 2023-04-17
Filing date: 2024-04-17
Publication date: 2024-10-24

Abstract

Disclosed are polyelectrolyte complexes (PECs) made from cationic and anionic water-soluble polyesters. These plastics are suitable for being broken down by seawater, and preferably are biodegradable. Also disclosed are cationic and anionic polyesters, and a method of making a polyelectrolyte complex

Description

Title: Polyelectrolyte Complex

Field

The invention relates to a polyelectrolyte complex material. Particularly, the invention relates to a saloplastic material as such, more specifically a seawater- decomplexable saloplastic material, methods of making such materials, and methods of using these materials.

Background

Poly electrolytes are generally soluble in water, driven by interactions between water and charge-bearing units. When two polyelectrolytes bearing opposite charges are combined together, they form a stable complex, i.e. a polyelectrolyte complex or “PEC”.

Whilst PECs had originally been known to yield rigid, non-moldable, brittle materials, it has been found that they can be provided with plastic properties. As a parallel to thermoplasticity, the corresponding property of polyelectrolyte complexes has been dubbed “saloplasticity”.

As explained in a background reference by Porcel and Schlenoff , (Biomacromolecules, 2009, 10, 2968-2975), salt does for a polyelectrolyte complex what temperature does for thermoplastics. Accordingly, it has been known to prepare saloplastic materials by means of salt-doping of PECs. An overview is given by Schaaf and Schlenoff in Adv. Mat., 2015, 27, 2420-2432. Herein it is reiterated that PECs heavily plasticized (doped) with salt water could be compacted into tough, macroscopic articles under ultracentrifugal fields. In addition, compacted PECs (CoPECs) having various shapes (such as fibers, rods, tapes, and tubes) could be prepared by extrusion. The standard material in the field of saloplastic PECs is a complex of poly(styrene sulfonate) (PSS) and poly(diallyldimethylammonium) (PDADMA) as polyanion and polycation, respectively. It is desired, however, to provide a greater versatility of saloplastic materials. Particularly, saloplastic PECs are sought that match better with today’s demand for more ecologically friendly plastics. This demand pertains, inter alia, to the non-biodegradable nature of PSS/PDADMA, and to the fact that this known PEC is composed of fossil-based polyolefin polymers. Accordingly, alternative saloplastic PECs are sought, and preferably non-fossil based, biodegradable, or both.

Background references on polyelectrolytes, not related to saloplastics, include EP2277562 and GB1463175. The former discloses an absorbable mixture of oppositely charged, solid microparticulate polyelectrolytes having its charges on terminal groups of the polymer chains involved. The latter relates to a process for preparing complex polyelectrolytes that are insoluble in water, and soluble in an organic medium.

Summary

In order to better address one or more of the aforementioned desires, the invention provides, in one aspect, a polyelectrolyte complex comprising a first water-soluble polymer the repeating units of which comprise units bearing anionic groups associated with a second water- soluble polymer the repeating units of which comprise units bearing cationic groups, wherein said first and second polymers are polyesters.

In another aspect, the invention presents a method of making a polyelectrolyte complex, the method comprising: (i) providing an aqueous composition comprising a water-soluble anionic polymer comprising repeating units that are negatively charged;

(ii) providing an aqueous composition comprising a water-soluble cationic polymer comprising repeating units that are positively charged;

(iii) combining the aqueous compositions so as to allow the anionic and cationic polymers to form a polyelectrolyte complex;

(iv) obtaining the polyelectrolyte complex by separating it from the water, wherein said anionic and cationic polymers are polyesters.

In yet another aspect, the invention concerns a plastic formulation comprising a polyelectrolyte complex comprising a first water-soluble polymer bearing anionic groups associated with a second water-soluble polymer bearing cationic groups, wherein said first and second polymers are polyesters, and one or more additives.

In a further aspect, the invention provides plastic articles made of the foregoing polyelectrolyte complex.

In a still further aspect, the invention presents novel cationic and anionic polyesters satisfying, respectively, the formulae

wherein n = is an integer of from 50 to 150;

Ri and R2 each independently represent an aliphatic, cycloaliphatic, heterocyclic, or aromatic moiety, preferably selected from the group consisting of (CH2)m with m being an integer of from 2 to 6, furanylene, isohexidylene, and phenylene; Rs and R4 each independently are selected from the group consisting of methyl, ethyl, propyl, butyl, and pentyl;

X is selected from the group consisting of F, Cl, Br, and I; M is metal, preferably Na.

Detailed description

In a broad sense, the invention is based on the judicious insight to circumvent the necessity of using vinylic polymers as a system to create PECs and, specifically, to utilize polyesters as functional polymers. Surprisingly, polyester -based PECs can be provided that do not require salt doping in order to become plasticized.

In order for anionic and cationic polymers to be capable of forming a polyelectrolyte complex, two basic requirements apply. One is that a solvent is available with which the polymers are sufficiently miscible, preferably soluble, in order to create an environment in which the actual complexation can take place. The other is that the polymers are capable of forming a complex that can be separated from the solvent.

One purpose of the present invention is to better address the environmental friendliness of the polymers. It will be understood that, to this end, the desired solvent is water. Accordingly, both the anionic polyester and the cationic polyester are water-soluble. Accordingly, the process of the invention comprises providing an aqueous composition comprising a water-soluble anionic polyester and an aqueous composition comprising a water-soluble cationic polyester.

The skilled person is familiar with the effects on water-solubility of the chemical structure of repeating units and side groups of a polymer. The skilled person is also familiar with the potential effect of chain-length on water- solubility. Preferably, the anionic and cationic polyesters applied in the present invention, will be designed such as to have a water solubility in a range of from 0.05 Mol/L to 1 Mol/L.

Further, a simple test is available to check the polyesters’ water- solubility. Reference is made to the OECD Guideline for the testing of chemicals; Test No. 105; adopted 27.07.95 “Water Solubility.”

It will be understood that, by comprising repetitive units having an anionic, respectively a cationic charge, the polyesters are capable of forming a complex. I.e., upon combining the two aforementioned aqueous compositions, the anionic polyester and the cationic polyester (being dissolved in water or blended with water) will come into contact with each other, and will swiftly, possibly instantaneously, form a polyelectrolyte complex.

In order for this complex to be obtained as a useful material, it needs to be separated from water. This can be done by evaporation until a solid or liquid PEC is obtained as a residue. Preferably, the PEC formed from the dissolved individual anionic and cationic polyesters, forms a separate liquid phase, or precipitates as a solid, without a need to evaporate water. In the event that the PEC precipitates as a result of combining the two aforementioned aqueous compositions, the precipitate can be obtained by any technique to remove a solid from a liquid, such as by filtration. In the event that the PEC forms a separate liquid phase, said phase can be obtained using any technique to remove one separate liquid phase from the other, such as by decanting.

Without wishing to be bound by theory, the present inventors believe that this ability to phase-separate or precipitate can be tuned by adapting either or both of the molecular weight and the charge density of the polyesters. E.g., with a sufficiently high molecular weight of the polymers, the resulting complex will precipitate from the water. The skilled person is aware of factors affecting the formation, and precipitation, of a PEC. This generally relates to the ion site, charge density, polyelectrolyte concentration, pH, and ionic strength. It will be understood that polycations and polyanions having a lower charge density along their chains, will require higher molecular weights to precipitate as a PEC, than the same polymer chains having a higher density of charged groups. The test of whether a combination of polycations and polyanions results in PEC formation is simple, since the precipitation or lack thereof of a PEC in water, can be simply determined visually. In the event of a non-precipitating mixture of polyanion and polycation, the skilled person will know how to increase either or both of charge density and molecular weight. Charge density can be elegantly tuned by applying chargeable or charged comonomers and non-charged, non-chargeable comonomers, in any desired ratio. A background reference representing the common general knowledge in the field is Kulkarni et al., Artificial Cells, Nanomedicine, and biotechnology, 2016, Vol.44, No.7, 1615-1625.

Particularly, the polymers of the present invention benefit from the effect of the electrolytic strength of a solvent, such as water, on the stability of a PEC. Accordingly, at the end of life, the PECs can be dissolved in ionic (typically NaCl or KBr) solutions, allowing the complex to be become disassociated, and thereby obtaining the corresponding polyelectrolytes. This means, e.g., that polymeric articles made from the PECs of the invention when ending up in sea, will quickly be falling apart. It will be understood that the resulting separate polyelectrolytes are still polymer waste that had preferably be removed from the environment. Nonetheless, the decomplexation effectively destroys the articles as such, which considerably aids to reduce the risks for the environment.

The precipitated or separated phase can be liquid or solid. At the same time, the anionic and cationic polyesters will generally need to have a sufficient water- solubility, without themselves precipitating from water. In order to achieve the foregoing, the anionic and cationic polyesters each preferably have a number-averaged molecular weight (M_n) of 1 kDa to 200 kDa, such as 2 kDa to 100 kDa, such as 5 kDa to 80 kDa, such as 10 kDa to 60 kDa, more preferably 30 kDa to 50 kDa. Suitable polymers may also have a molecular weight in a range of from 7.5 kDa to 20 kDa, such as 10 kDa to 15 kDa. In accordance with common general knowledge, M_n is determined with Size Exclusion Chromatography.

It is conceivable to prepare the PEC by providing water, and dissolving the anionic and cationic polyesters, simultaneously, sequentially, or alternatingly. It is also conceivable to provide a solution of either of the two polyesters, cationic or anionic, and add the corresponding other polymer to such solution. For the sake of better controlling the composition of the complexes formed, i.e., better controlling the ratio of the anionic and cationic polyesters, it is preferred to first provide separate aqueous solutions of both of the polyesters, and then add the solutions to each other, preferably gradually. In all of the foregoing embodiments, the polymers and/or polymer solutions are generally blended with each other, so as to allow the desired complexation to occur. The blending can be accomplished by mixing, stirring, or otherwise by applying any suitable technique available to the skilled person. The blending will generally be done for a period of 30 seconds to 30 minutes. Shorter blending times, e.g. 5-30 seconds can be suitable as well, preferably with high-speed stirring or vigorous mixing, e.g. at more than 500 rpm. Longer blending times, e.g. 5 minutes to 1 hour or more, can be employed as well. In conformity with the common general knowledge in the art, the optimal blending speeds and time to allow complexation to occur, will differ also according to the scale of the production equipment and amount of loading.

The water in which the monomers are dissolved, preferably is deionized water. The anionic and cationic polyesters are blended, and preferably dissolved, generally in a concentration range, calculated on the basis of the molecular weight of a single repeating unit, of 0.01 M to 1 M, preferably 0.05 M to 0.5 M, more preferably 0.08 M to 1.0 M. The anionic and the cationic polyester can be blended in a broad range of molar ratios. Generally, the molar ratio, calculated on the basis of the molecular weight of the repeating unit, is in a range of from 90:10 to 10:90, such as 20:80 to 80:20, such as 70:30 to 30:70, such as 60:40 to 40:60, such as 50:50. The foregoing ranges hold in the event that both the anionic and the cationic repeating unit have the same number of charged groups (generally 1-3, such as 2, more typically 1). In the event that the number of charged groups is different for either polyester, the above molar ratio’s will be adapted accordingly. E.g., a ratio of 50:50 if both repeating units contain

1 charged group, will be adapted to a ratio of cationic polyester : anionic polyester of 33.33 : 66.67 in the event of the cationic polyester having

2 charged groups per repeating unit, and the anionic polyester having 1 charged group per repeating unit.

In accordance with the invention, the polyelectrolyte complexes are generally made by a method comprising:

(i) providing a water-soluble anionic polyester comprising repeating units that are negatively charged;

(ii) providing a water-soluble cationic polyester comprising repeating units that are positively charged;

(iii) dissolving the anionic polyester in water;

(iv) dissolving the cationic polyester in water;

(v) contacting the dissolved anionic and cationic polyesters with each other so as to allow forming a polyelectrolyte complex; and

(vi) obtaining the polyelectrolyte complex by separating it from the water.

The polyester PECs of the invention can be obtained as a phase- separated liquid or precipitated solid, with the aqueous phase from which it is formed remaining as a supernatant. This can be accomplished over time by allowing the aqueous phase to stand until phase separation or precipitation occurs. Preferably, the phase separation is further aided by centrifugation, e.g. at 2000 rpm to 6000 rpm, such as 3000 rpm to 5000 rpm, for 2 minutes to 20 minutes, such as 5 minutes to 15 minutes. The PECs can generally be obtained by decanting the supernatant, or by any other suitable techniques available to the skilled person to remove a supernatant or to collect a precipitate.

The obtained polyester PECs of the invention are preferably subjected to dehydration, before further processing and shaping. The dehydration can be done by available drying techniques. A preferred method to process polyester PECs obtained as a highly viscous liquid, is to spread the liquid on an inert (non-stick) sheet, e.g., a Teflon sheet, and heat in an oven or a heated press (without necessarily pressing at this stage). Generally, a sticky solid will result. This sticky solid can be subjected to compression molding, such as hot pressing on a sheet such as above, or in a desired different mold, followed by cooling. The skilled person will be able for a specific polymer to determine a suitable temperature for heating. A generally applicable temperature ranges from room temperature (such as 18 °C) to 120 °C, preferably 60 °C to 110 °C, more preferably 70 °C to 90 °C. Further, equipment generally available in industrial production can be applied, such as, e.g., belt dryers, fluidized bed dryers, roller/drum dryers, trough dryers, hot air (heat-pump) dryers. For a given PEC the skilled person will be able to simply determine its thermostability, and take this into account in choosing which dehydration technique and equipment had best be used.

From the obtained PECs, plastic formulations can be made on the basis of compounding techniques available in the field. A typical method is extrusion, and generally (as with known plastics) a variety of additives can be added for various purposes. From these plastic formulations, various plastic articles can be produced, generally by means of known plastic conversion routes, such as injection molding, sheet extrusion, and thermoforming. The PECs of the invention are particularly suitable for foil-type applications, such as plastics used for food packaging or plastics used in the agriculture or horticulture to cover plants or soil, other packaging plastics, or, e.g., plastic shopping bags.

The aforementioned known vinylic PECs are saloplastics, requiring doping with salt (typically sodium chloride) in order to become sufficiently plasticized to be eligible for practical use. By their polyelectrolyte nature, then plasticity of the present polyester PECs can be affected by salt as well. In fact, the inventors investigated these materials as saloplastics. However, it was surprisingly found that the addition of salt as a plasticizer was, in fact, unnecessary for the invented PECs. Without wishing to be bound by theory, the inventors believe that this effect is obtained by virtue of the comparatively larger distance between the charged groups in the polymer than in many vinyl saloplastics PECs. This reflects an essential difference between vinylic polymers and polyester polymers. In the case of vinylic polymers, the polymeric backbone is determined by repeating carbon-carbon unit, with all further parts of the original vinylic monomer becoming equally repetitive side groups. In the case of polyesters, even with the smallest monomers, the distance between repeating groups will always include an ester group. Further, the choice for polyesters to produce saloplastics, synergistically enables benefiting from the easier breaking down of ester bonds, than of the carbon-carbon bonds in vinylic polymers. Moreover, other than in vinylic polymers, the size of the monomer chain between the functional groups (carboxylic or hydroxyl) will be built in into the polyester backbone. This, of course, is a known structural phenomenon of polyesters. However, it has not hitherto been realized to make advantageous use hereof in providing anionic and cationic polymers that can be employed in producing PECs. Particularly, this relation between the monomer structure and the polymer backbone allows various finetuning possibilities. These include choosing monomers with shorter or longer chains or, e.g., building in one charge per repeating unit, or more, e.g. 2 or 3, charges per repeating unit. Notwithstanding the above, if it were desired for a specific PEC of the invention to further promote plasticity, such can be done by adding salt. The skilled person will be able to determine using regular skills the amount of salt needed to further promote plasticity.

The synthesis of polyesters as such does not require any elucidation to the skilled person. Generally, this synthesis involves the polycondensation of a difunctional carboxylic monomer, such as a dicarboxylic acid or carboxylic derivative such as ester or acid chloride, with a diol (dihydroxyl compound). The charged polyesters employed in preparing the PECs of the invention can be made generally in two ways. One is to first provide a charged diol or charged dicarboxylic monomer, and then combine it to a suitable comonomer in the polycondensation reaction. The other is to first provide a non-charged polyester, and then provide the polymer with the desired charge (either cation or anion) at desired density that is suitable to form a polyelectrolyte complex. In that event the monomers should be chosen such as to have active groups that are eligible to be provided with a negative, respectively positive charge. For charged polyesters having a molecular weight of 15 kDa or lower, the former method is preferred. Also, generally, the method to start from charged monomers is preferred for the anionic polyesters. The direct polycondensation of charged monomers provides maximum control over the polymer architecture, and in particular the charge distribution. Generally, charged polyesters having a relatively high molecular weight, such as above 20 kDa are preferably prepared by the post-modification of an uncharged polyester. Such post-modification preferably involves the quaternarization of nitrogen, such as performed with methyl iodide or ethyl iodide. Suitable chargeable groups include carbon-carbon double bonds, which can be transformed into sulfonate groups, and secondary or tertiary amines, which can be converted into ammonium groups. Generally preferred charged groups are anionic SO.3 , POzf, SO.3 Na⁺ or SO3H, and, cationic, NH4⁺, NHi⁺X (with X being a halide, preferably Cl", Br , or I ). Post-modification can also be conducted, as another preference, on the basis of click chemistry. Click reactions are known to the skilled person, a preferred example being the thiol — ene click pair. Thus, e.g., providing the monomers with a thiol group, will make them chargeable via reaction, after polymerization, with an alkene carrying a charged group (or an alkene that itself carries a chargeable group). Or, vice versa, providing the monomers with an alkene side-group, and after polymerization reacting this with a charged (or chargeable) molecule comprising a thiol group.

The choice of polyesters as the polymeric backbone for cationic and anionic polymers to be complexed into PECs, provides for a further advantage. This relates to the versatility, which is greater than with vinylic polymers, in tuning the charge distribution. The PECs of the invention are generally formed from polyesters made by the polycondensation of charged or chargeable dicarboxylic and dihydroxyl monomers. With this type of polymerization, it is relatively easy to build in non-charged or non-chargeable building blocks. This presents an advantageous versatility by allowing the charge distribution in either or both of the polymers to affected at will. Alternatively, polyesters can be applied that are prepared from hydroxy acids, e.g., ferulic aid, caffeic acid, or by ring-opening polymerization of lactones such as, e.g., angelica lactones or 5-hydroxy furanone.

An advantage of the PECs of the present invention, is that they provide a type of plastic that can be disintegrated by salt water, as this results in decomplexation of the PEC, yielding the separate anionic and cationic polyesters. This particularly holds for the preferred PECs that do not require salt doping to become plasticized. Rather, the addition of salt water will result in reducing or fully breaking down the association between the anionic and cationic polyesters that forms the complex. It will be understood that the salt-water decomplexation of the PECs of the invention is an important step in diminishing the detrimental effects of the amounts of plastics ending up in sewers and, ultimately in the sea. This phenomenon is a worldwide environmental challenge, known as the “plastic soup”.

Particularly, in the cold, bacteria- and fungi-poor environment of the oceans, materials do not tend to biodegrade well.

In sea water, the PECs of the present invention will at least be reduced to their constituent polyesters, which are not unharmful to the environment, but clearly less so than the original plastic articles.

An interesting advantage of choosing polyesters as the constituent polymers of PECs, relates to their further degradation in the environment. As such, polyesters are believed to be better biodegradable than vinylic polymers. This already provides for a synergistic effect with the salt-water degradation of the PEC structure. Moreover, the judicious choice of specifically using polyesters in order to produce PECs, opens up a range of possibilities to produce PECs on the basis biodegradable polymers. Accordingly, the present inventions provides the possibility of producing polymers that are biodegradable and have a desirable combination of suitable properties during both processing and use, yet combined with degradation at a sufficient rate, specifically in sea water.

By way of further preference, the PECs of the present invention are made of polyesters that are made from bio-based monomers or from the substrates that can be obtained from the biomass feedstocks. This, too, presents a further synergy with the salt-based degradability of the PECs, thereby presenting an advantage that cannot be achieved with the pre-existing vinylic PECs:

Suitable monomers that can possibly be obtained directly or indirectly from a biological include the following:

(I) [ct, 6] -unsaturated lactones:

suitable for charging to either a cation or an anion at a monomer stage or after polymerization;

(II) unsaturated dicarboxylic acids and diols:

wherein R is methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, or tertiary butyl, suitable for charging to either a cation or an anion at a monomer stage or after polymerization;

(III) nitrogen containing neutral monomers:

with R indicating methyl, ethyl, or aryl (typically phenyl or pyridyl); or

with R indicating methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, or tertiary butyl; these are suitable for charge to a cation at a monomer stage, or after polymerization;

(IV) anionic monomers:

with R indicating methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, or tertiary butyl;

The monomers (I-IV) are suitable to synthesize either cationic or anionic polyesters. Particularly the monomers (I-III), in combination with appropriate comonomers respectively, may be employed directly to prepare neutral polymers. The “unsaturated carbon-carbon double bonds” or active “N” atoms present in the resulting polymers provide a way to introduce charge in the subsequent step to produce either cationic or anionic polyester. Alternately, the charge can be introduced in the monomer stage for the structures mentioned in I-III. The examples depicted in category (IV) represents anionic charged monomers and thus polymerizable directly resulting in an anionic polyester.

To functionalize “unsaturated carbon-carbon double bonds” or active “N” atoms, a skilled person may typically use the Aza-Michael addition reaction or N-alkylation reaction respectively to introduce either cationic or anionic charge in the monomer or polymer. For example, primary or secondary amine-containing sulfonic acid sodium salt can be used as a Michael donor that undergoes an addition reaction in the carbon-carbon double bond (Michael acceptor) and facilitates the introduction of the anionic group (S0.3 Na⁺). In the latter case, alkyl halide may be used to introduce the cationic charge in the “N” atom. The alkyl group may vary from carbon chain length 1-10, but preferably methyl, ethyl and pentyl; halide anions vary from fluoride (F-), chloride (Cl-), bromide (Br-) and iodide (I-) but preferably (Cl-), (Br-) and iodide (I-).

To tune the thermal and overall plastic properties of the resulting polyelectrolyte polymer, a skilled person, for example in the monomer category (I-IV), may alter the carbon chain length varying from 1-5 but preferably 1-3. Further, the skilled person is familiar with choosing comonomers that also play a vital role in achieving the above-said desired properties.

The above monomers and comonomers can be synthesized either directly or from intermediates that can be provided from biomass or other biological resources. The compounds such as but not limited to phthalates/terephthalates, succinate, adipate, amino acids, amino ethanol, benzyl amine, itaconic acid, piperidine, maleic/fumaric acid, 1,4-butane diol, 1,3-propane diol, ethylene glycol, lactones, etc. are suitable to synthesize monomers for producing saloplastics. As such, the synthesis of desirable monomers can be accomplished on the basis of chemical synthesis techniques and reaction that are known to the skilled person. Suitable chemical reactions include carbon-carbon direct coupling, Aza-Michael addition, A-alkylation, esterification, carbon-addition, oxidation, reduction, and sulfonation technologies. In the event that catalysis is employed this preferably is heterogeneous catalysis, as this is easier in downstream processing, and since heterogeneous catalysts have a potential to be recycled and/or reused in the subsequent runs.

Charged monomers can be synthesized on the basis of either or both of the dicarboxylic monomer and the dihydroxyl monomer (respectively the hydroxy acid or lactone polymer). These monomers will then be subjected to polycondensation with a preferably bio-based corresponding monomer, for which diols and diacids are commercially well available.

In both the anionic and the cationic polyester, the polymeric backbone can be aliphatic, aromatic, or a combination of the two, provided that the polyesters are water-soluble.

In an interesting embodiment, the cationic polyester is all aliphatic, having a quaternized amine within the polymeric backbone. An example hereof has the following repeating unit, Formula (I):

(I).

Herein I- (iodide) is indicated as a negative counterion. As person skilled in the art will understand, other anions are equally possible. E.g., other anions that result from methylation of the nitrogen atom, such as chloride or bromide, or any other anion resulting from a possible ion exchange step. Preferably the anion is chloride (Ch).

In an interesting embodiment, the anionic polyester is partly aromatic, having a sulfonic acid negatively charged group. An example hereof has the following repeating unit, Formula (II):

Herein Na⁺ (sodium ion) is indicated as a positive counterion. As person skilled in the art will understand, other cations are equally possible, optionally resulting from a possible ion exchange step. Preferably the cation is sodium ion. Surprisingly, all polyester PECs made in accordance with the invention possess mechanical properties that present an improvement over vinylic PECs. Accordingly, these polyester PECs were found to be more flexible than vinylic PEC, and to show an elongation at break that is even up to ten-fold higher than that of vinyl-based PECs. The invention also pertains to a plastic formulation comprising a polyelectrolyte complex as described hereinbefore, in any of the described embodiments, and one or more additives, e.g. reinforcing fillers such as chalk or talc. Also the invention provides plastic articles made of a polyelectrolyte complex according to the PECs presented in the present disclosure. Generally, to this end the PEC is subjected to compression forces e.g. by compression molding or by extrusion; the resulting articles can have shapes (e.g., films, fibers, rods, tapes, or tubes).

The invention will be illustrated hereinafter with reference to the following non-limiting examples.

Example 1: Synthesis of polvanion

Dimethyl 5 -sulfoisophthalate sodium salt (100.0 g, 0.331 mol) and ethylene glycol (300.0 mL, 5.354 mol) were charged into a round bottom flask and heated to 120 °C. To this suspension was added titanium isopropoxide (2.0 mL, 0.007 mol) and the suspension was heated to 195 °C (reflux temperature) under nitrogen atmosphere and continued for 3.0 h. Then the suspension was cooled down to room temperature and kept overnight in the fume hood. The reaction mixture was filtered over a glass filter and ethylene glycol was removed by high vacuum distillation. The residue after distillation solidifies to a white crystalline solid. The mass was collected and finely grinded with a pestle and mortar. Then washed with 400 ml acetone and dried in vacuo at 40 °C until a constant weight was obtained (112.8 grams, 96%). Next, a pre-dried 30 mL drying flask was charged with ethylene glycol end-capped sodium 5 -sulfoisophthalate. The set-up was inserted into a glass oven (B-585 Kugelrohr glass oven), evacuated and refilled with gaseous nitrogen three times. The oven was heated to 220 °C for 48 h. After completion of the reaction, the mixture was cooled down to room temperature under a nitrogen atmosphere, and the polymer was isolated in quantitative yield.

Example 2: Synthesis of polycation

A pre-dried 100 mL three-necked round bottom flask was equipped with a mechanical stirrer and Claisen distillation head and cooler was charged with dimethyl succinate (14.050 g, 96.139 mol), N- methyldiethanolamine (14.87 g, 124.81 mol, 1.3 equiv.) and titanium isopropoxide (27 mg, 0.1 mol%). The flask was evacuated and filled with nitrogen three times. The mixture was heated to 210-215 °C and stirred with 100 rpm. After 2 h the pressure was gradually decreased to 25 mbar in 30 min. After 15 min at 25 mbar, the pressure was further reduced to 0.02 mbar and the temperature was kept at 210-215 °C. After 4 h the reaction mixture was cooled to room temperature under a nitrogen atmosphere yielding a dark brown viscous liquid.

A round bottom flask equipped with a reflux condenser with a nitrogen inlet, and dropping funnel was charged with polymer (14.93 g) and dissolved in THF. A mixture of methyl iodide (32.48 g) in THF was added dropwise. Immediately a brownish precipitates started to form. Next, the methyl iodide and THF were decanted and the polymer was washed a few times with THF. The resulting brownish material was dried under reduced pressure using an oil pump (50 °C, 0.04 mbar), with a yield of 23.45 g (92%).

Individual solutions of polyanion and polycation were prepared by dissolving the polyelectrolyte in deionized water (0.1 M with respect to the repeating unit, 2-20 mL). Both poly electrolyte solutions were poured simultaneously in a 15 mL or 50 mL centrifuge tube (Greiner Bio-One) equipped with a magnetic stirring bar while stirring at high speed (>500 rpm). After 30 s, the stirring was stopped, the stirring bar was removed and the PEC solution was centrifuged at 4000 rpm for 10 min. The supernatant was removed and the oily PEC was washed with deionized water by vigorously shaking. Again the solution was centrifuged at 4000 rpm for 10 min, and the washing water was decanted.

Dense PEC films were prepared by compression molding using a hydraulic press (PHI, United States of America). Rectangular or square molds were cut from a Teflon sheet (~120 gm thickness) with sizes varying from 1x2 cm² up to 4x4 cm². Alternatively, a steel mold with 5x5 cm2 squares with a thickness of 550 gm was used. First, the oily PEC was dehydrated by spreading it on a Teflon sheet, and drying it in the press at 80 °C without any pressure applied for 10 min. The PEC was collected as a sticky solid. Next, the solid was charged into the Teflon/steel mold placed on top of a metal plate covered with a Teflon sheet. The mold was covered with another Teflon sheet and metal plate and the whole sandwich was placed inside the hot press. The PEC was heated at 80 °C for 5 min without pressure, thereafter 5 kton pressure was applied for another 5 min. Then the heating was switched off and the press was actively cooled with tap water. When the temperature in the press reached below 40 °C the pressure was released and the PEC film was removed from the mold.

Claims

1. A poly electrolyte complex comprising a first water-soluble polymer the repeating units of which comprise units bearing anionic groups associated with a second water-soluble polymer the repeating units of which comprise units bearing cationic groups, wherein said first and second polymers are polyesters.

2. A poly electrolyte complex according to claim 1, wherein the anionic groups and cationic groups are side groups.

3. A polyelectrolyte complex according to claim 1 or 2, wherein the anionic polyester and cationic polyester each have a number-averaged molecular weight (M_n) of 10 kDa to 60 kDa, M_n being determined with Size Exclusion Chromatography.

4. A polyelectrolyte complex according to claim 3, wherein the anionic polyester and cationic polyester each have an M_n of 30 kDa to 50 kDa.

5. A polyelectrolyte complex according to claim 1 or 2, wherein the anionic polyester and cationic polyester each have a number-averaged molecular weight (M_n) in a range of from 7.5 kDa to 20 kDa, M_n being determined with Size Exclusion Chromatography.

6. A polyelectrolyte complex according to claim 5, wherein the anionic polyester and cationic polyester each have an M_n of 10 kDa to 15 kDa.

7. A polyelectrolyte complex according to any one of the preceding claims wherein the cationic polyester comprises a repeating unit according to Formula (I):

with I- representing iodide as a negatively charged counterion, or any other anion.

8. A polyelectrolyte complex according to any one of the preceding claims wherein the anionic polyester comprises a repeating unit according to Formula (II):

with Na⁺ representing sodium ion as a positively charged counterion, or any other cation.

9. A plastic formulation comprising a polyelectrolyte complex according to any one of the preceding claims, and one or more additives.

10. A plastic article comprising a polyelectrolyte complex according to any one of the claims 1 to 8.

11. A cationic polyester satisfying the formula

wherein n = an integer of from 50 to 150; Ri and R2 each independently represent an aliphatic, cycloaliphatic, heterocyclic, or aromatic moiety, preferably selected from the group consisting of (CH2)m with m being an integer of from 2 to 6, furanylene, isohexidylene, and phenylene;

R3 and R4 each independently are selected from the group consisting of methyl, ethyl, propyl, butyl, and pentyl;

X is selected from the group consisting of F, Cl, Br, and I.

12. An anionic polyester satisfying the formula

M is metal, preferably Na.

13. A method of making a poly electrolyte complex, the method comprising:

(i) providing an aqueous composition comprising a water-soluble or water anionic polymer comprising repeating units that are negatively charged;

(iii) combining the aqueous compositions so as to allow the anionic and cationic polymers to form a polyelectrolyte complex; (iv) obtaining the polyelectrolyte complex by separating it from the water, wherein said anionic and cationic polymers are polyesters.

14. A method according to claim 13, wherein the aqueous composition comprising the anionic polyester is an aqueous solution of said polyester.

15. A method according to claim 13 or 14, wherein the aqueous composition comprising the cationic polyester is an aqueous solution of said polyester.

16. A method according to any one of the claims 13 to 15, wherein the anionic and cationic polyesters are dissolved, in a concentration range, calculated on the basis of the molecular weight of a single repeating unit, of 0.05 M to 0.5 M.

17. The method of claim 16, wherein the concentration range is 0.08 M to 1.0 M.

18. A method according to any one of the claims 13 to 16, wherein the polyesters are in accordance with either or both of claims 11 and 12.