FR3101876A1 - Process for preparing an epoxidized diene elastomer. - Google Patents

Abstract

The invention relates to a process for the mass preparation of an epoxidized diene polymer in a rubber processing tool which comprises the addition at least twice of a solid epoxidizing agent. The process of the invention makes it possible to achieve an epoxidation rate comparable to the epoxidation rates obtained during the epoxidation process of diene polymer in solution, with a high yield greater than or equal to 85%.

Description

Process for the preparation of an epoxidized diene elastomer.

The field of the present invention is that of the mass preparation of an epoxidized diene elastomer.

Elastomers based on conjugated diene monomers are widely described in the literature and used daily for their many applications, mainly for their elasticity property.

Epoxidized diene polymers have come to enlarge the offer of these diene polymers by proposing to broaden the possible applications due to the presence of epoxide functional groups in the polymer chain. Thus, for example, the epoxidation of diene polymers makes it possible to envisage an alternative crosslinking to that usual by means of sulfur-based vulcanization systems. The epoxide functions of the epoxidized polymers can also be used to graft these polymers with molecules bearing a part reactive with these epoxide functions. It is thus possible to envisage, for example, functionalizing a polymer along its chain by grafting appropriate functions.

Epoxidized diene polymers and processes for obtaining them are well known to those skilled in the art. Conventionally, the epoxidation can be carried out using an epoxidizing agent such as a peracid or hydrogen peroxide in the presence of a carboxylic acid, with or without a catalyst. Diene polymer epoxidation processes described in the literature can be classified into 2 types, namely "solution" processes when the diene polymer is re-dissolved in an organic solvent and "bulk" processes when the diene polymer remains in a solid state.

The epoxidation rate is the molar ratio of the number of epoxy functions in the polymer to the number of carbon-carbon double bonds in the polymer. The epoxidation rates described in the literature depend on the type of epoxidation process used. With "solution" epoxidation processes, it is possible to achieve rates in excess of 10%. With "mass" processes the rate of epoxidation is generally described as not going beyond 6% to 8%. Whatever the type of epoxidation process, the reaction time is generally long and can be counted in several hours, often incompatible with an economically profitable industrial implementation.

As a "solution" process, mention may be made of EP 2530094 A1 which describes a solution process aimed at dissolving a diene polymer in an organic solvent and at epoxidizing it by reaction with metachloroperbenzoic acid (mCPBA) as of epoxidizing agent for about two hours at room temperature, in the presence of a catalyst. It is thus possible to achieve epoxidation rates of around 12% with yields of over 90%.

Bulk processes also react diene polymers with a peracid which can be produced in-situ or ex-situ. "Bulk" processes can be implemented in two different ways: the polymer, which always remains in a solid state, can react in bulk or reduced to a granular or powder state. If the polymer is transformed into granules or powder, the epoxidation reaction is carried out in a stirred reactor to generate a suspension of the polymer in a solution of the peracid. The reaction can also be done in an extruder fed with granules. Otherwise, when the diene polymer is in bulk, the reaction can be carried out in a mixer or even an extruder.

Thus, EP 0810237 A1 describes a mass epoxidation process according to which the diene polymer is in the form of powder or granules. The polymer is suspended in an organic solvent which should not dissolve the polymer, for example ethyl acetate. Peracetic acid or performic acid, formed in situ, is used as an epoxidizing agent and reacts for several hours. An epoxidation rate of 0.2% to 4% is obtained. Similarly, EP 1403287 A1 describes solid phase epoxidation with peracetic acid. A diene polymer is suspended in water with talc and heated above 30°C. A solution of peracetic acid in ethyl acetate is gradually added and the reaction takes place for several hours. The examples show that epoxidation rates of 1.5% to 3.0% are achieved.

The process described in RU2509780 C1 was developed for the epoxidation of polybutadiene fibers formed by electrospinning. The fibers are suspended in a stirred reactor in a mixture of a carboxylic acid and hydrogen peroxide in the presence of a catalyst. The various epoxidizing agents are formed in situ. The epoxidation time varies from one to four hours and the temperature from 10°C to 30°C. Following the reaction, the fibers are washed with distilled water and dried under vacuum. Variable epoxidation rates are obtained depending on the reaction conditions and are between 1 and 8% with low yields of less than 30%.

CN1113906 C, which deals with the bulk epoxidation of 1,4-trans polyisoprene, describes epoxidation rates greater than 20% in a time reduced to one hour. However, it should be noted that the epoxidation rate was measured indirectly by the consumption of the epoxidizing agent. However, this consumption can be linked to parasitic reactions and not only to epoxidation. Also, the effective epoxidation rates given in this document are uncertain.

JP5598365 B2 and JP5541125 B2 describe mass epoxidation processes for diene polymers used in bulk without prior shaping. In the examples, the diene polymer is contacted first with stearic acid on heated rollers and, after a number of passes, with hydrogen peroxide. Different epoxidation rates are obtained varying from 0.8% to less than 3% depending on the temperature used in the mixer set at 50°C or 60°C.

CN 1263902 A describes an epoxidation process according to which the diene polymer can be loaded in bulk into an internal mixer of the Banbury type or an extruder, in the absence of any solvent. A solid peracid in the presence of a dispersing additive is also fed into the mixer or extruder. For example, BRs are epoxidized in small internal laboratory mixers with solid phthalic monoperacid in the presence of talc for a period of 15 minutes at temperatures of 20°C, 25°C and 30°C. Measured epoxidation rates are between 5% molar and 8% molar, without however specifying the measurement protocol. Assuming that it is the epoxy groups that are dosed for this measurement, the epoxidation yields are between 50% and 70%.

It emerges from the study of the prior art that it is not easy, with a mass epoxidation process, to achieve epoxidation rates as high as those obtained during the "solution" process and this in times compatible with an implementation on an industrial scale. It also emerges from the study of the state of the art that when satisfactory epoxidation rates can be obtained in mass, they are obtained with an insufficient yield for a productive, economically profitable process.

The problem that the invention proposes to solve is therefore to provide a process for the mass epoxidation of diene polymers making it possible to obtain epoxidation rates of the same order as those obtained "in solution" in an acceptable time for a setting. implemented on an industrial scale.

The invention also aims to provide a process for the mass epoxidation of diene polymers which is productive and compatible with an economically profitable industrial application with a satisfactory yield.

In this perspective, the invention also aims to provide an epoxidation process that is simple to implement.

The inventors have developed a process for the mass preparation of an epoxidized diene polymer that is simple and productive to produce, compatible with deployment on an industrial scale, which makes it possible to achieve epoxidation rates of the order of those obtained "in solution" with a high yield, for example greater than 80%, and this in a short time.

Thus, a first object of the invention is a process for the mass preparation of an epoxidized diene polymer which comprises, in a rubber processing tool, bringing a diene elastomer into contact with an epoxidation of peracid type in solid form, which epoxidation agent is introduced in at least two stages, the epoxidation reaction being able to take place at room temperature and for a short duration, which in certain cases can be less than one hour.

The process for the mass preparation of an epoxidized diene polymer according to the invention comprises
- the loading of a diene polymer in a rubber processing tool,
- the addition, in at least two steps, of an epoxidizing agent chosen from solid peracids,
- mixing after each addition of epoxidizing agent in the implementation tool.

Preferably, according to the process of the invention, the diene polymer is a diene elastomer chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene-styrene copolymers (SBR), butadiene-ethylene copolymer, butadiene-ethylene-styrene copolymer, isobutene-isoprene copolymer, isoprene-styrene copolymer (SIR), isoprene-butadiene copolymer (BIR) and isoprene-butadiene-styrene copolymers (SBIR).

Preferably, according to the process of the invention, the tool for implementing the rubber is a roller mixer

Preferably then, the method comprises, after loading the diene polymer, a step of repeated passage of the diene polymer over the rollers in order to uniformly cover said rollers with a continuous layer of polymer.

Preferably, according to the method of the invention, the mixer is equipped with a temperature regulation device.

Preferably, according to the method of the invention, the epoxidizing agent is solid in the form of powder, granules or any other similar form.

Preferably, according to the process of the invention, the epoxidizing agent is chosen from aromatic peracids, preferably from perbenzoic acid and its derivatives and monoperphthalic acid and its derivatives, more preferably from halogenated perbenzoic acids. In particular, the epoxidizing agent is metachloroperbenzoic acid.

Preferably, according to the process of the invention, the total quantity of epoxidizing agent added is at most 100% molar and greater than 0% molar, more preferably it is at least 5% molar. Preferably, according to the process of the invention, the quantities of epoxidizing agent introduced at each addition are less than or equal to a quantity Qm ±1% molar of epoxidizing agent making it possible to achieve a stabilized epoxidation yield at least 85%, preferably at least 90%, more preferably 100%, in a single addition.

Preferably, according to the method of the invention, the number of additions or steps for adding the epoxidizing agent is greater than or equal to the whole part of the ratio of the total quantity of epoxidizing agent to a quantity Qm, Qm being a quantity of epoxidizing agent making it possible to achieve a stabilized epoxidation yield of at least 85%, preferably at least 90%, more preferably 100%, in a single addition.

Preferably, according to the process of the invention, the mixing time after each addition of epoxidizing agent is at least equal to the time tm necessary to reach the stabilized epoxidation yield of at least 85%, preferably at least 90%, more preferably 100%, for a given quantity Qm of epoxidizing agent added all at once, Qm being a quantity of epoxidizing agent making it possible to achieve a stabilized epoxidation yield of at least 85%, preferably at least 90%, more preferably 100%, in a single addition.

Preferably, according to the process of the invention, the quantity of epoxidizing agent introduced at each addition is less than or equal to a quantity denoted Qm±1% molar of epoxidizing agent, the number of addition steps of epoxidizing agent is greater than or equal to the whole part of the ratio of the total amount of epoxidizing agent to the amount Qm and the mixing time after each addition of epoxidizing agent is preferably at least equal to time tm, Qm being a quantity of epoxidizing agent making it possible to achieve this stabilized epoxidation yield of at least 85%, preferably at least 90%, more preferably 100%, in a single addition and tm is the time required to reach this stabilized epoxidation yield.

Preferably, according to the process of the invention, the quantity of epoxidizing agent introduced at each addition is at least 1.5% molar and less than 8% molar.

Preferably, according to the process of the invention, the number of additions of epoxidizing agent is greater than or equal to 2 and less than or equal to 10.

Preferably, according to the process of the invention, the mixing time after each addition of epoxidizing agent is less than or equal to 20 minutes,

Preferably, according to the method of the invention, one of the following characteristics is respected, preferably two, preferably three, preferably four, preferably five, preferably all:
- the diene polymer is a butadiene polymer, preferably a polybutadiene,
- the rubber application tool is a roller mixer,
- the epoxidizing agent is a perbenzoic acid or one of its derivatives, preferably metachloroperbenzoic acid,
- the quantity of epoxidizing agent added at each addition step is less than or equal to a quantity Qm, Qm being a quantity of epoxidizing agent making it possible to achieve a stabilized epoxidation yield of at least 85 %, preferably at least 90%, more preferably 100%, in a single addition, preferably Qm being at least 1.5 mol% and less than 8 mol%, more preferably still at most 5 mol%
- the number of additions of epoxidizing agent is greater than or equal to the whole part of the ratio of the total quantity of epoxidizing agent to the quantity Qm, the number of additions preferably being less than or equal to 5 , preferably still less than or equal to 4,
- the mixing time after each addition of epoxidizing agent is greater than or equal to a time tm, tm being the time necessary to reach a stabilized epoxidation yield of at least 85%, preferably at least 90%, more preferably 100%, for a quantity Qm of epoxidizing agent added all at once, preferably tm being at least 3 minutes,.

Description of figures

Figure 1 is a graph illustrating the evolution of the yield as a function of time of an epoxidation reaction of a polybutadiene in a roller mixer by adding an epoxidizing agent all at once.

Figure 2 is a graph illustrating the evolution of the yield and the evolution of the epoxidation rate as a function of time of an epoxidation reaction of a polybutadiene in a roller mixer by successive addition of an epoxidizing agent according to the invention.

detailed description

In the present description, any interval of values denoted by the expression "between a and b" represents the range of values greater than "a" and less than "b" (i.e. limits a and b excluded) while any interval of values denoted by the expression “from a to b” signifies the range of values going from “a” to “b” (that is to say including the strict limits a and b).

In the present description, unless otherwise expressly indicated, all the percentages (%) indicated are percentages (%) molar.

In the present description, the term "mass process" means a process carried out in a reaction medium not comprising any solvent.

The invention relates to a process for the bulk preparation of an epoxidized diene polymer which comprises
- the loading of a diene polymer in a rubber processing tool,
- the addition, in at least two steps, of an epoxidizing agent chosen from solid and soluble peracids in the diene polymer,
- mixing after each addition of epoxidizing agent.

By diene polymer is meant according to the invention, any type of polymer derived at least in part (i.e. a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).

The diene polymer may be chosen from the group consisting of thermoplastic diene polymers, thermoplastic elastomers, diene elastomers and mixtures thereof. Preferably, the diene polymer is chosen from diene elastomers.

Among diene elastomers, mention may be made of elastomers comprising units of a 1,3-diene monomer. By 1,3-diene monomer unit is meant a unit which results from the insertion of a 1,3-diene monomer into a growing polymer chain. In a known manner, the units of a 1,3-diene monomer can result from a 1,2 or 1,4 insertion of the 1,3-diene monomer in the polymer chain. In the case of a 1,4 insertion, they can be in the cis or trans configuration.

As 1,3-diene monomer, mention may be made of those having 4 to 8 carbon atoms, such as for example 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, isoprene, piperylene. Also suitable are their halogenated derivatives, such as for example chloroprene. The 1,3-diene monomer can also consist of a mixture of these monomers, in which the 1,3-diene monomer units consist of the monomer units of each of the monomers comprising the mixture. Preferably, the 1,3-diene is 1,3-butadiene, isoprene or a mixture thereof.

In particular, the diene elastomer is advantageously a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), polybutadienes (BR), butadiene copolymers, isoprene copolymers and mixtures of these elastomers. Such copolymers are more preferably chosen from the group consisting of butadiene-styrene copolymers (SBR), ethylene-butadiene copolymers, ethylene-butadiene-styrene copolymers, isoprene-butadiene copolymers (BIR) , isoprene-styrene copolymers (SIR), isoprene-butadiene-styrene copolymers (SBIR) and mixtures of such copolymers.

The above diene elastomers can be, for example, block, random, block, microblock. They can be modified in particular by coupling or starring.

By rubber processing tool is meant a mixer suitable for mixing reaction media of high viscosity such as that of bulk diene elastomers of the type described above.

Thus, the mixer can be a roller mixer, an extruder, a mixer equipped with an agitation system such as those described in the book David B. Todd, Mixing of Highly Viscous Fluids, Polymers, and Pastes, in Handbook of Industrial Mixing: Science and Practice, E.L. Paul, V.A. Atiemo-Obeng, and S.M. Kresta, Editors. 2004, John Wiley and Sons. Page 998, Page 1021, specifically a double Z-arm mixer, an internal mixer with intermeshing rotors, other internal mixers….

By roller mixer is meant, in the sense known to those skilled in the art, any type of external mixer having two parallel horizontal rollers, which can be cooled or heated, rotating in opposite directions, usually at different speeds, their spacing being adjustable, and allowing mastication and mass mixing of a polymer or a polymer composition.

By extruder in the context of the invention, is meant an extruder or co-extruder provided with at least two injection points along its mixing cavity in order to be able to add the epoxidizing agent in at least twice the along the gradual path of the polymer in said cavity. In order to control the heat of the epoxidation reaction, the extruder can also be equipped with a cooling system over all or part of the length of the mixing cavity and have a specific profile to minimize self-heating.

By double-arm mixer in Z (or sigma) in the context of the invention, we mean for example mixers with blades in Z or sigma equipped with a discharge screw such as "sigma blades mixer-discharge screw type" marketed by Battaggion SPA, "extrusion-kneader" marketed by Aachener Misch- und Knetmaschinenfabrik Peter Küpper GmbH & Co. KG, "double-z-kneader with extrusion screw" marketed by Hermann Linden Maschinenfabrik GmbH & Co. KG. , "mixer extruders", marketed by Aaron Process Equipment Company.

By internal mixer with intermeshing rotors in the context of the invention, is meant for example a mixer as described in the document US4775240 and marketed under the name "VIC" (Variable Intermeshing Clearance, that is to say internal mixer with meshing rotors and variable clearance).

Other internal mixers include, for example, instrumented laboratory mixers of the Measuring Mixer 350 type marketed by the Brabender company.

According to a preferred embodiment of the invention, the tool for implementing the rubber is a roller mixer. The choice of such a mixer makes it possible to better control the heat of the reaction, the mixer being open.

Preferably, after loading the bulk diene polymer into the rubber processing tool, the latter is mixed for a few minutes. This step aims to relax the polymer for better incorporation of the epoxidizing agent.

According to the embodiment of the invention according to which the mixer is a roller mixer, the kneading step is carried out by repeatedly passing the diene polymer over the rollers until the rollers are uniformly covered with a continuous layer of polymer .

Thus, preferably according to this embodiment, the polymer is kneaded by repeated passage over the rollers until it forms a continuous sheet uniformly covering the rollers (also called sleeving). This mixing or sleeving step can last several minutes. Its duration depends in particular on the nature of the diene polymer and on the temperature. By way of illustration, this step can last up to 20 minutes, preferably up to 10 minutes.

After this mixing time, the epoxidizing agent is added at least twice.

The epoxidizing agent is introduced into the rubber processing tool, in the solid state in the form of powder, granules or another similar form.

The epoxidizing agent is advantageously a compound with strong oxidizing power. Preferably, the epoxidizing agent is an organic peracid. As organic peracids, mention may be made of aliphatic carboxylic peracids and aromatic carboxylic peracids.

Preferably, the epoxidizing agent is an aromatic carboxylic peracid. More preferentially then, the epoxidizing agent is chosen from perbenzoic acid and its derivatives and monoperphthalic acid and its derivatives. By way of derivatives of perbenzoic acid, mention may be made of halogenated perbenzoic acids and nitro perbenzoic acids. Among these perbenzoic acid derivatives, metachloroperbenzoic acid will be particularly preferred as epoxidizing agent.

The epoxidizing agent is added in sequence in at least two times in the mixer in order to maintain satisfactory epoxidation performance. This addition in several times makes it possible to achieve a yield greater than or equal to 85%, preferably greater than or equal to 90%. This increases the productivity of the method according to the invention compared to the mass methods of the prior art.

The total amount of epoxidizing agent used in the process according to the invention is not limited and depends on the desired degree of epoxidation. The total amount of epoxidizing agent added is greater than 0 mole % expressed with respect to the total number of moles of carbon-carbon double bonds of the diene polymer. However, advantageously, the total quantity of epoxidizing agent is at least 5% molar. Although having no upper limit, the total quantity of epoxidizing agent added is preferably at most 100% molar. According to certain variants of the process, the total quantity of epoxidizing agent added is at most 50% molar. According to other variants of the process, the total quantity of epoxidizing agent is at most 25% molar, preferably at most 15% molar. Thus, advantageously, the total quantity of epoxidizing agent is at least 5% molar and at most 15% molar.

A person skilled in the art will know how to determine the total quantity of epoxidizing agent necessary to obtain the desired degree of epoxidation of the diene polymer, in particular the total quantity of epoxidizing agent may correspond to the desired degree of epoxidation. The total quantity of epoxidizing agent is the sum of the quantities of epoxidizing agent introduced at each addition.

Advantageously, according to one implementation of the invention, the quantity of epoxidizing agent introduced at each addition is less than or equal to a quantity denoted Qm of epoxidizing agent. This quantity Qm is a quantity of epoxidizing agent making it possible to achieve, in a single addition, a stabilized epoxidation yield of at least 85%, preferably at least 90%, more preferably 100%, for a diene polymer given in the same rubber processing tool.

According to the invention, the amount of epoxidizing agent added at each addition step has no minimum limit. It is best to distribute the amounts of epoxidizing agent as evenly as possible at each addition step.

It is up to those skilled in the art to define the value of Qm allowing them to achieve a stabilized epoxidation yield of at least 85% depending on the epoxidizing agent or the elastomer matrix to be epoxidized. This Qm value can be determined experimentally in a simple manner within the reach of those skilled in the art. A method for determining a Qm value is described below and in the examples that follow.

The number of additions or steps for adding the epoxidizing agent, according to an advantageous implementation of the invention, is an integer greater than or equal to the ratio of the total amount of epoxidizing agent to the quantity Qm.

According to the invention, the number of additions of epoxidizing agent is at least 2. The maximum number of additions is not limited in itself. However, for reasons of industrial reality and with the aim of limiting the steps of the method, this number is preferably less than or equal to 10.

According to an advantageous implementation of the invention, the mixing time after each addition of epoxidizing agent is preferably at least equal to the time tm necessary to reach the stabilized epoxidation yield of at least 85%, of preferably at least 90%, more preferably 100%, for an amount Qm of epoxidizing agent added all at once in a rubber processing tool. The time tm is measured from the addition of the epoxidizing agent.

It is up to those skilled in the art to define the value of tm allowing them to achieve a stabilized epoxidation yield of at least 85% depending on the epoxidizing agent or the elastomer matrix to be epoxidized. The time tm can be determined experimentally in a simple manner within the reach of those skilled in the art. A method for determining tm is described below and in the examples which follow.

Although there is no maximum limit on the mixing time after each addition, too long a mixing time could result in reduced process productivity. The mixing time after each addition of epoxidizing agent is preferably less than or equal to 20 minutes.

According to a particularly advantageous implementation of the invention, the quantity of epoxidizing agent introduced at each addition is less than or equal to a noted quantity Qm of epoxidizing agent, the number of steps for adding the epoxidizing agent is an integer greater than or equal to the ratio of the total quantity of epoxidizing agent to the quantity Qm and the mixing time after each addition of epoxidizing agent is preferably at least equal to the time tm. According to this implementation, it is possible to further optimize the epoxidation yield of the process according to the invention for high epoxidation rates.

Those skilled in the art will understand that the tm and Qm values depend essentially on the nature of the diene polymer, more particularly on the ability of its carbon-carbon double bonds to be epoxidized, on the nature of the epoxidizing agent, on the operating conditions…

A quantity Qm and a time tm can be determined experimentally in a simple manner within the reach of those skilled in the art. Qm and tm can be determined by carrying out in the same tool for implementing the rubber and according to the same operating conditions, in particular the setpoint temperature, the mixing time, as well as the operating parameter of the mixer, the epoxidation of a same diene polymer with an amount Qi of the same epoxidizing agent added at one time. Several Qi quantities of the epoxidizing agent can be tested. We study the evolution as a function of time of the yield of the epoxidation reaction for a quantity Qi of epoxidizing agent introduced at one time. The reaction yield is determined according to the method described later. The evolution of this function forms an asymptotic type curve whose asymptote is horizontal (see Figure 1 for example). The term stabilized epoxidation yield is then understood to mean the value at the ordinate of the asymptote horizontal to this curve. A quantity Qi=Qm corresponds to a quantity of a given epoxidizing agent for which the value at the ordinate of the asymptote is greater than or equal to 85%, preferably at least 90%, more preferably 100%. The time tm corresponds to the time required, from the addition of the epoxidizing agent, for a determined quantity Qm of agent, to arrive at the asymptote, that is to say to reach a yield of stabilized epoxidation of at least 85%, preferably at least 90%, more preferably 100%.

By way of illustration and referring to Figure 1, two epoxidation tests of a polybutadiene were carried out in the same roller mixer and under the same operating conditions (in particular of tool for processing the rubber, of setpoint temperature, sleeving time, as well as the speed and gap of the tool rollers). For each of these tests, a certain quantity Qi of epoxidizing agent (metachloroperbenzoic acid or m-CPBA) is introduced into the mixer all at once.

A first test consists of adding Qi=8 molar% of m-CPBA all at once. The evolution of yield as a function of time, illustrated by the graph in Figure 1, forms an asymptotic type curve whose asymptote is horizontal and has a value on the ordinate of the order of 60%. Thus, the value Qi=8% molar is not a quantity Qm according to the invention, since the value at the ordinate of the asymptote is not greater than or equal to 85%.

The second test consists of adding 3.2 mol% of m-CPBA all at once. The evolution of yield as a function of time, illustrated by the graph in Figure 1, forms an asymptotic type curve whose asymptote is horizontal and has a value on the ordinate of the order of 90%. Thus, the value Qi=3.2% molar is a quantity Qm according to the invention, since the value at the ordinate of the asymptote is greater than or equal to 85.

We can graphically determine the value of tm for this quantity Qm=3.2% molar. The epoxidation yield of 90% is reached after 4 minutes from the addition of m-CPBA. So tm is 4 minutes.

According to a variant of the invention, it is possible to use a compound for aiding the dispersion of the epoxidizing agent in the polymer. As dispersing aid compounds, mention may be made of mineral powders such as talc, kaolin, silica and other similar compounds, as well as mixtures thereof. When such a compound is used, the epoxidizing agent and the dispersion aid compound are advantageously mixed prior to their use in the process of the invention.

According to the invention, the bulk epoxidation process can achieve high epoxidation rates with high yields at set temperatures around ambient. Thus, preferably the setpoint temperature of the epoxidation process according to the invention varies from 20° C. to 30° C., preferably from 23° C. to 27° C. and is advantageously room temperature, i.e. of the order of 25 °C, at normal pressure. Too high a temperature would have the disadvantage of possibly initiating the degradation of the epoxide groups formed or even possibly initiating the thermal decomposition of the peracid, thus reducing the yield of the process.

Insofar as the epoxidation reaction is exothermic, the temperature can be maintained within these ranges of variation if necessary by cooling the reaction system by means of cooling devices which may be fitted to the rubber processing tool. For example, for a roller mixer, the interior of the rollers can be hollow, thus allowing the circulation of liquids which are used to control the setpoint temperature and to minimize local self-heating.

The use of a roller mixer as a rubber processing tool has the advantage, insofar as it is open, of better controlling the heat of the epoxidation process.

According to a particular implementation of the invention, the method has at least one of the following characteristics, preferably two, preferably three, preferably four, preferably five, preferably all:
- the diene polymer is a butadiene polymer, preferably a polybutadiene,
- the rubber application tool is a roller mixer,
- the epoxidizing agent is a perbenzoic acid or one of its derivatives, preferably metachloroperbenzoic acid,
- the quantity of epoxidizing agent added at each addition step is less than or equal to a quantity Qm, , Qm being a quantity of epoxidizing agent making it possible to achieve a stabilized epoxidation yield of at least 85%, preferably at least 90%, more preferably 100%, in a single addition, which quantity Qm is preferably at least 1.5 mol% and less than 8 mol%,
- the number of additions of epoxidizing agent is an integer greater than or equal to the ratio of the total quantity of epoxidizing agent to the quantity Qm, preferably less than or equal to 5, more preferably less than or equal to 4 ,
- the mixing time after each addition of epoxidizing agent is greater than or equal to a time tm, tm being the time necessary to reach a stabilized epoxidation yield of at least 85%, preferably at least 90%, more preferably 100%, for a quantity Qm of epoxidizing agent added all at once, which tm is preferably at least 3 minutes.

According to this particular implementation of the invention, the method has at least one of the following characteristics, preferably two, preferably three, preferably four, preferably five, preferably all:
- the diene polymer is a polybutadiene,
- the rubber application tool is a roller mixer,
- the epoxidizing agent is metachloroperbenzoic acid,
- the quantity of epoxidizing agent added at each addition step is at least 1.5% molar and less than 8% molar,
- the number of additions of epoxidizing agent is less than or equal to 5, preferably still less than or equal to 4,
- the mixing time after each addition of epoxidizing agent is greater than or equal to a time tm is at least 3 minutes.

At the end of the epoxidation reaction, a bulk epoxidized diene polymer is recovered.

Advantageously, according to the process of the invention, it is possible to prepare an epoxidized diene polymer exhibiting a high epoxidation rate in view of the epoxidation rates achievable by the bulk methods of the state of the art, with a yield of at least 85%, preferably at least 90%, in a limited time.

The epoxidized diene polymer obtained at the end of the process according to the invention can be used in various applications known to those skilled in the art depending on its nature.

Examples

Measurement methods used

Dosage of epoxide groups in the epoxidized diene polymer/

Spectral characterization and measurements of the epoxidized BR polymer microstructure are carried out by liquid phase Nuclear Magnetic Resonance (NMR) spectroscopy.

For these measurements, a Bruker Avance III HD 400 MHz spectrometer is used, equipped with a Bruker cryo-BBFO z-grad 5 mm probe.

1H experiments are recorded using a radiofrequency pulse with a tilt angle of 30°, the number of repetitions is 64 with a recycle delay of 5 seconds.

The experiments are carried out at 25°C.

25 mg of sample are dissolved in 1 mL deuterated chloroform (CDCl3).

Structure of an epoxidized polybutadiene

The axis of the 1H chemical shifts is calibrated against the signal of the protonated impurity of the solvent (CHCl3) at δ1H = 7.2 ppm.

The chemical shifts of the signals characteristic of this matrix are presented in table 1 of attribution of 1H signals of epoxidized polybutadiene in CDCl3.

The quantifications were carried out from the integration of the 1D 1H NMR spectra using the Topspin software.

The integrated signals for the quantization of the different patterns are:
I1 = between 6.0 and 5.00 ppm: 1H -CH= ethylenic of BR1-2 + 2H –CH=CH- ethylenic of BR1-4
I2 = between 5.00 and 4.60 ppm: 2H = ethylenic CH2 of the BR1-2 units
I3 = between 3.20 and 2.55 ppm: 2H -CH-CH- epoxy units.

They are then normalized as follows:
1H BR1-4 = (I1-I2)/2 = A
1H BR1-2 = I2/2 = B
1H Epoxide = I3/2 = C

The quantification of the microstructure is carried out in molar percentage (% molar) as follows:
%molar BR1-4 / BRepoxidized = A/(A+B+C)
Molar % BR1-2 / BRepoxidized = B/(A+B+C)
Molar % Epoxide / BRepoxidized = C/(A+B+C)

Epoxidation rate

The measured epoxidation rate is therefore the molar percentage ratio of epoxy groups to the sum of the molar percentages of epoxy groups and carbon-carbon double bonds (BR1-4 and BR1-2)

So :
Measured epoxidation rate (%) = (C / (A+B+C)) x 100

Yield

The yield is calculated as being the ratio of the measured epoxidation rate to the targeted epoxidation rate.

So :
Yield (%) = (Measured epoxidation rate/ Target epoxidation rate) x 100
With
• target epoxidation rate = number of moles of m-CPBA / number of moles of carbon-carbon double bonds
• Number of moles of C=C double bonds = Number of moles of the diene part, ie the number of moles of BR in the examples.
• Number of moles of the diene part = mass of the diene part (g) / molar mass of the diene unit,
Either in the examples
Number of moles of BR = mass of BR (g) / molar mass of a polybutadiene unit (54 g/mol)

Examples 1

Reagents:
BR: microstructure in % by mass (0.5% 1.2 unit, 97% 1.4 cis unit, 2.5% 1.4 trans unit)
m-CPBA: metachloroperbenzoic acid at 172.57 g/mol
m-CBA = metachlorobenzoic acid at 156.57g/mol
m-CPBA used in the examples is 77% pure by mass, the remainder being m-CBA

The epoxidation of BR by a peracid was studied in a roller mixer Ø 100 from Scamex with oil circulation.

Epoxidation process of a BR with single addition of 8% molar m-CPBA

- 200g (3.70mol) of BR is injected into the roller mixer. Following the passage between the rollers, a film of BR is obtained around the front roller and a bead is formed induced by the air gap and the difference between the speed of the front and rear roller. The air gap corresponds to the distance which separates the two rollers. It is set at 1mm and is kept constant throughout the mixing time. The speed of the rear roller corresponds to 80% of the speed of the front roller which is fixed at 5 rpm and kept constant throughout the mixing time. The set temperature is set at 25°C.
- After 10 minutes a continuous film of rubber is obtained.
- 66.40g of 77% pure m-CPBA is then injected (0.296 mol, ie 8% molar of 3.70 mol of BR) into the bead and the epoxidation reaction begins.
- a rubber sample is taken from the rollers every minute up to 5 minutes, then at 7, 10, 15 and 20 minutes, to measure the epoxidation rate and the yield

NB: since m-CPBA is 77% pure by weight, this represents 66.40g (i.e. 51.13 of m-CPBA and 15.27g of m-CBA)

BR epoxidation process with one-time addition of 3.2 molar % of m-CPBA

- 200g (3.70mol) of BR is injected first. Following the passage between the rollers, a film of BR is obtained around the front roller and a bead is formed induced by the air gap and the difference between the speed of the front and rear roller. The air gap corresponds to the distance which separates the two rollers. It is set at 1mm and is kept constant throughout the mixing time. The speed of the rear roller corresponds to 80% of the speed of the front roller which is fixed at 5 rpm and kept constant throughout the mixing time. The set temperature is set at 25°C.
- after 10 minutes a continuous film of rubber is obtained
- 26.43 g of 77% pure m-CPBA is then injected (0.118 mol, ie 3.2 mol% of 3.70 mol of BR) into the bead and the epoxidation reaction begins.
- a rubber sample is taken from the rollers every 5 minutes up to 30 minutes, then every 10 minutes up to 60 minutes, to measure the rate of epoxidation and the yield.

NB: since m-CPBA is 77% pure by mass, this represents 26.43g (i.e. 20.35 of m-CPBA and 6.08g of m-CBA)

Figure 1 illustrates the evolution of the yield as a function of time of the epoxidation reaction of polybutadiene in a roller mixer by adding an epoxidizing agent all at once. The two curves appearing on the graph illustrate for one the addition in one go of 8% molar of m-CPBA and for the other the addition in one go of 3.2% molar of m-CPBA.

Figure 1 shows that the introduction of an 8% molar amount of m-CPBA at one time does not allow a yield greater than 75% to be achieved, even by extending the reaction time. The evolution of the yield as a function of time describes an asymptotic curve whose asymptote, reached after approximately 7 minutes, is horizontal with a value on the ordinate of the order of 60%, i.e. an epoxidation rate by 4.8%.

Figure 1 also shows that the introduction at one time of an amount of 3.2% molar m-CPBA makes it possible to achieve a yield greater than 85%. The evolution of the yield as a function of time describes an asymptotic curve which reaches its asymptote after 4 minutes from the addition of the epoxidizing agent. The asymptote is horizontal with a value at the ordinate of the order of 90%. However, only a low epoxidation rate of 2.9% is achieved with such a high yield.

Examples 2

BR epoxidation process with sequenced addition of 8% total molar m-CPBA according to the invention.

The operating conditions are identical in terms of the roller mixer used, the nature of the BR, the set temperature, etc., as for the two previous processes.

Determination of Qm, tm and N

The curve in Figure 1 is used which illustrates the evolution of the yield as a function of time of the polybutadiene epoxidation reaction in a roller mixer by adding an epoxidation agent all at once. It is noted that the introduction in one go of a quantity of 3.2% molar m-CPBA makes it possible to achieve a yield of the order of 90%. The value of Qm is then fixed at 3.2% molar. Thus, to achieve an epoxidation yield greater than 85%, the amount of m-CPBA to be added at each addition step is less than or equal to 3.2 mol%.

The asymptote of the curve is reached after 4 minutes from the addition of the epoxidizing agent. tm is therefore 4 minutes. Thus the mixing time D after each addition is at least 4 minutes.

It is desired to epoxidize a BR with 8% molar total of m-CPBA. The number of addition N is at least 3 (integer greater than or equal to 8 / 3.2).

We set N=3 and D=10 minutes. The quantity of m-CPBA to be added at each addition step is less than or equal to 3.2% (Qm), the sum of the quantities added being equal to 8 mol%.

Epoxidation process

200g (3.70mol) of BR is injected into the roller mixer. Following the passage between the rollers, a film of BR is obtained around the front roller and a bead is formed induced by the air gap and the difference between the speed of the front and rear roller. The air gap corresponds to the distance which separates the two rollers. It is set at 1mm and is kept constant throughout the mixing time. The speed of the rear roller corresponds to 80% of the speed of the front roller which is fixed at 5 rpm and kept constant during the process. The set temperature is set at 25°C.
After 10 minutes a continuous film of gum is obtained,
a first part (0.118 mol or 3.2 mol%) of the total peracid (m-CPBA) (0.296 mol) is injected into the bead and the epoxidation reaction begins at this instant denoted t0.
At t1=t0+10 minutes approximately a second part of the total peracid is injected (0.089mol or 2.4% molar)
At t2=t0+20 minutes the third and last part of the total peracid is injected (0.089mol or 2.4% molar)
a gum sample is taken before each new addition of m-CPBA to measure the rate of epoxidation and the yield of the reaction.

Figure 2 illustrates the evolution of the yield and of the epoxidation rate as a function of time of the polybutadiene epoxidation reaction in a roller mixer by adding an epoxidizing agent in three times, according to the invention. The two curves appearing on the graph illustrate for one the evolution of the yield of the epoxidation reaction as a function of time and for the other the evolution of the rate of epoxidation as a function of time when the addition of 8 Molar % of m-CPBA is produced in three times respectively from a first quantity of 3.2% molar and twice of 2.4% molar.

Figure 2 shows that the introduction in several times of a total quantity of 8% molar m-CPBA makes it possible to achieve a yield of the order of 95% after 30 minutes of reaction. Figure 2 shows that the introduction in 3 times with mixing for 10 minutes at the end of each addition, of a total quantity of 8% molar m-CPBA makes it possible to achieve a yield of the order of 95 % after 30 minutes of reaction. The evolution of the epoxidation rate shows that an epoxidation rate of 7.6% is reached.

It emerges from these tests that the method according to the invention, sequencing the addition of an epoxidizing agent, makes it possible to prepare in mass an epoxidized diene polymer exhibiting a high epoxidation rate, of the same order as the epoxidation rates obtained with epoxidation processes in solution, with a high yield that can reach values greater than or equal to 80%.

Indeed, one can for example consider aiming for BR epoxidation rates much higher than that of this test, in particular greater than 10%, by adding the epoxidizing agent m-CPBA in fractions of at most 3, 2% molar until the target rate is reached. Thus, it will be possible to obtain a high yield greater than or equal to 80% and an epoxidation rate close to the targeted epoxidation rate.

The method according to the invention is more productive than the mass methods of the prior art and limits the stages of treatment of the polymer to be epoxidized and of recovery of the epoxidized polymer. The process according to the invention makes it possible to achieve higher rates of epoxidation of the polymer by mass than the mass processes of the prior art.

Claims (15)

A process for the bulk preparation of an epoxidized diene polymer which comprises
- the loading of a diene polymer in a rubber processing tool,
- the addition, in at least two steps, of a solid epoxidizing agent,
- mixing the diene polymer with the epoxidizing agent, after each addition of the epoxidizing agent to the rubber processing tool, Process according to Claim 1, characterized in that the diene polymer is a diene elastomer chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), copolymers of butadiene- copolymers (SBR), butadiene-ethylene copolymers, isobutene-isoprene copolymers, isoprene-styrene copolymers (SIR), isoprene-butadiene copolymers (BIR) and isoprene-butadiene- styrene (SBIR). Method according to any one of the preceding claims, characterized in that the implementation tool is a roller mixer. Process according to the preceding claim, characterized in that the loading of the polymer into the roller mixer is followed by a step of repeated passage of the diene polymer in order to uniformly cover the rollers with a continuous layer of polymer Process according to any one of the preceding claims, characterized in that the epoxidizing agent is solid in the form of powder, granules or any other analogous form. Process according to any one of the preceding claims, characterized in that the epoxidizing agent is chosen from aromatic peracids, preferably from perbenzoic acid and its derivatives and monoperphthalic acid and its derivatives, more preferably from halogenated perbenzoic acids, most particularly the epoxidizing agent is metachloroperbenzoic acid. Process according to any one of the preceding claims, characterized in that the total quantity of epoxidizing agent added is at most 100% molar and greater than 0% molar, more preferably it is at least 5% molar, which quantity is expressed relative to the number of moles of carbon-carbon double bond of the diene polymer. Process according to any one of the preceding claims, characterized in that the quantity of epoxidizing agent introduced at each addition is less than or equal to a quantity Qm of epoxidizing agent making it possible to achieve a stabilized epoxidation yield at least 85%, preferably at least 90%, more preferably 100%, in a single addition. Process according to any one of the preceding claims, characterized in that the number of additions or stages of addition of the epoxidizing agent is an integer greater than or equal to the ratio of the total quantity of agent epoxidation with a quantity Qm of epoxidation agent, Qm being a quantity of epoxidation agent making it possible to achieve a stabilized epoxidation yield of at least 85%, preferably at least 90%, more preferentially of 100%, in just one addition. Process according to any one of the preceding claims, characterized in that the mixing time after each addition of epoxidizing agent is at least equal to the time tm necessary to reach the stabilized epoxidation yield of at least 85%, preferably at least 90%, more preferably 100%, for a quantity Qm of epoxidizing agent added all at once, Qm being a quantity of epoxidizing agent making it possible to achieve this stabilized epoxidation yield d at least 85%, preferably at least 90%, more preferably 100%, in a single addition. Process according to any one of the preceding claims, characterized in that the quantity of epoxidizing agent introduced at each addition is less than or equal to a quantity denoted Qm of epoxidizing agent, the number of addition steps of epoxidizing agent is an integer greater than or equal to the ratio of the total amount of epoxidizing agent to the amount Qm and the mixing time after each addition of epoxidizing agent is preferably at least equal at time tm, which Qm is a quantity of epoxidizing agent making it possible to achieve a stabilized epoxidation yield of at least 85%, preferably at least 90%, more preferably 100%, in a single addition and where tm is the time required to reach this stabilized epoxidation yield. Process according to any one of the preceding claims, characterized in that the quantity of epoxidizing agent introduced at each addition is at least 1.5% molar and less than 8% molar, which quantity is expressed relative to the number of moles of carbon-carbon double bond of the diene polymer. Process according to any one of the preceding claims, characterized in that the number of additions of epoxidizing agent is greater than or equal to 2 and less than or equal to 10. Process according to any one of the preceding claims, characterized in that the mixing time after each addition of epoxidizing agent is less than or equal to 20 minutes. Process according to any one of the preceding claims, characterized in that it has at least one of the following characteristics, preferably two, preferably three, preferably four, preferably five, preferably all:
- the diene polymer is a butadiene polymer, preferably a polybutadiene,
- the mixer is a roller mixer,
- the epoxidizing agent is a perbenzoic acid or one of its derivatives, preferably metachloroperbenzoic acid,
- the quantity of epoxidizing agent added at each addition step is less than or equal to a quantity Qm, Qm being a quantity of epoxidizing agent making it possible to achieve a stabilized epoxidation yield of at least 85 %, preferably at least 90%, more preferably 100%, in a single addition, which Qm is preferably at least 1.5 mol% and less than 8 mol%
- the number of additions of epoxidizing agent is an integer greater than or equal to the integer part of the ratio of the total quantity of epoxidizing agent to a quantity Qm of epoxidizing agent, the number of addition being preferably less than or equal to 5, more preferably less than or equal to 4,
- the mixing time after each addition of epoxidizing agent is greater than or equal to a time tm, tm being the time necessary to reach a stabilized epoxidation yield of at least 85%, at least 90%, more preferably 100%, for a quantity Qm of epoxidizing agent added all at once, tm preferably being at least 3 minutes.