MX2012000550A - Method for obtaining polydienes in presence of ionic liquids. - Google Patents

Abstract

The present invention refers to the obtention of polydienes in presence of ionic liquids (Li's) using polymerizations in solution, via living anionic polymerization and Ziegler-Natta polymerization. n-Butyl-Lithium was used as a catalytic system in the case of the anionic polymerization and the tertiary system of neodymium versatate (NdV)/triisobutyl-aluminium (TIBA/diethyl aluminium chloride (DEAC) for the Ziegler-Natta polymerizations. The Li’s used were mainly of the imidazol type. The presence of liquids as additives in the reaction medium may reduce the maximum temperature of reaction, since these act as exothermic moderators of the reaction. In addition the liquids may interfere with the distribution of molecular weights. In both systems, anionic and Ziegler-Natta, the presence of Li’s reduces the heterogeneity of the chains.

Description

METHOD OF OBTAINING POLYDYNEN IN THE PRESENCE OF LIQUIDS IONICS DESCRIPTION OBJECT OF THE INVENTION The present invention relates to a method for producing polydienes, by living anionic polymerization and Ziegler-Natta in solution, which contains ionic liquids. The presence of these compounds makes it possible to reduce the increase in the temperature of the mixture derived from the high exothermicity of the reaction, while at the same time leading to the obtaining of polymers with low polydispersity indexes in their molecular weight.

BACKGROUND Ionic liquids (Li s) in polymerization reactions.

Ionic liquids are salts that consist of an inorganic cation and an anion, at room temperature they are liquids and generally do not exhibit vapor pressure. These compounds have several favorable characteristics, are liquid over a wide range of temperatures, (including temperatures above 300 ° C), have a low melting point. Even some LI's are flammable and non-explosive, in addition to having a high thermal stability [P. Kubiza in J. of Polym. Sci., Part A: Polym.Chem, 2005,43,4675]. They have the ability to dissolve different organic compounds (including initiators, monomers and polymers) and organometallic (metallocene catalysts, alkyl lithium initiators and catalysts based on rare earths). So the synthesis via radical, living anionic and coordination is entirely feasible. Also, given their ionic nature they can serve as highly polar solvents. On the other hand and perhaps one of the most important advantages of ionic liquids is that, due to their high heat capacity, they can act as moderators of exothermic reactions [R. Vijayaraghavan and cois. inAngew. Chem. Int. Ed, 2004, 43, 5363] by acting as absorbers of the heat generated by the reaction. With the above it is possible to prevent out of control or runaway reactions. This allows greater control over a complete environment of a polymerization reaction. As can be seen, these advantages can not be found in conventional organic solvents.

In relation to the processes for obtaining polymers, the mass polymerization method is well known to have certain advantages associated with a higher purity in the final products. However, it also brings with it various problems that have to do with uneven mixing and poor control of the temperature during the course of the reaction, given the considerable increase in viscosity. Due to these facts, solution polymerization is preferred in obtaining various polymers (both academically and industrially speaking) since it is possible to improve the problems associated with the transfer of energy and mainly by the reduction of viscosity. Although the drawback of this technique is the removal of the solvent from the polymer. In the case of using ionic liquids as solvents in polymerization reactions, it is possible to select adequately LI's that are soluble in water, for easy separation or to use LI's that are separated from the polymer during the reaction, so that through a process filter can easily separate the polymer.

As can be seen, the LI's present interesting characteristics from the point of view of the synthesis, as well as the obtaining process, which makes them potential substitutes for organic solvents.

Ziegler-Natta catalysts with neodymium as active species In general, we can say that the coordination catalysts most commonly used for the polymerization of conjugated dienes are a combination of metal compounds of groups 4 to 8 of the periodic table (3d group) or of the series of lanthanides and actinides (group 4f), in combination with alkylaluminums or alkylaluminium hydrides. It should be mentioned that in general, dienes that can not be subjected to bidentate coordination do not polymerize with lanthanide catalysts [W. Kuranen Principies of Coordination Polymerization, John Wiley & amp;; Sons Inc., 2001]. In polymerizations such as butadiene, the efficiency of the catalyst depends on the magnitude of the alkylation of the Nd compound, which in turn is determined by the nature of the aluminum alkyl cocatalyst, the molar ratio [Nd] / [A1] , as well as the stability of the Nd-C bonds, which depend on the temperature [C. Reny cois, in Polymer 2007, 48, 2470].

Polymerization by coordination of 1,3-diene monomers The rubbers coming from diene monomers have different isomers, which depend on the mode of addition of the same in the polymer chain, the pplisoprene can have 4 different isomers, while the polybutadiene, due to its symmetry, can only form three types: cis, trans and the lateral vinyl type, the latter formed in the addition of the monomer by carbons 1, 2, which would be equivalent to the 3,4 addition, as shown in Figure 1. [V. M. Litvinovy cois, in Spectroscopy of Rubbers and Rubbers Materials, RapraTechnology Limited, 2002].

Stereo-regularity in the polymerization of dienes depends on the type of catalyst, the binders and even the volume of the substituents contained in the diene. The formation of cis and trans structures are determined by the anti and syn structure of the last monomeric unit that binds to the catalyst and therefore to the growing chain. The conjugated dienes can be coordinated to the transition metal (Mt) by a double bond as in the trans-and] 2 case, or through two double bonds as in the cis-t cases} 4 and trans-t] 4. A monomer with trans configuration (such as liganteiram-2 and trans-r 4) is inserted between the metal-carbon bond, and the inserted monomer unit rotates around its central axis to accept the allylic r 3-syn structure in the growth of the chain. On the other hand, when a monomer is coordinated with cis configuration (as ligantecw-? 4) an n-allylic anti-structure is formed. On the other hand, when adding an electron donor (Lewis base), it occupies a coordination site, so the monomer can only be coordinated through a single double bond, and bidentate coordination is impossible. Therefore, if you have a catalytic system that generates cis polymer and you add some electron donor, the cis content will decrease. Conversely, when electron acceptors (Lewis acids) are added, coordination with the two double bonds of the diene is favored. Likewise, if an anti-form predominates at the end of the growing chain, the cis content increases [L. Porri et al., In Comprehensive Polymer Science, PergamonPress Oxford, 1989, 4]. This behavior has been observed in the synthesis of polybutadiene with high cis content when Nd catalysts are used, since there is a deficiency of electrons in the metal, this has the ability to coordinate at the same time the two diene double bonds [G. A. Aminova and cois. Theor.Found.Chem.Eng. 2006, 40, 59].

Living Anionic Polymerization Anionic polymerization occupies a key position in the industrial production of polyesters of the polydiene type (polybutadiene or polyisoprene) and other products. The development of the preparation of living ammonium polymers, that is, the systems in which the polymerization occurs in the absence of termination and chain transfer reactions, aroused considerable interest due to the varied potential of applications of this type of polymerization [M Fontanilleen Comprehensive Polymer Science, Pergamon Press, Great Britain, 1989, 3, 365]. In an anionic system, the stability of the active center can be maintained at high concentration for a prolonged period of time unlike some other types of polymerizations, such as the case of radical polymerization where a free radical has a longer half-life short, compared to a reactive center of ionic nature. In addition, the high reactivity of the active centers and their living character opens the way to new macromolecular structures with a well-defined structure [R. P. Quirk et al., In Anionic Polymerization, Principies and Practical Applications, Marcel Dekker, New York, 1996] which are inaccessible by other polymerization methods. These reactions require extreme conditions in the purity of reagents, solvents and equipment. A monomer can be polymerized ammonically if it meets the following two basic conditions [P. Remppy cois, in Polymer Synthesis, Huthing and Wepf Verlag, Berlin, 1986]: the double bond must be reactive towards the carbanionic reactive centers, and in turn the double bonds, must not present reactive sites towards the carbanionic species, since they could lead to the deactivation of these.

Thus, the main monomers that can be anionically polymerized are: styrene, dienes, vinylnaphthalene, vinylpyridimines, alkylmethacrylates, caprolactam, etc. As for the solvents, the number of solvents used in the anionic polymerization is limited due to the reactivity of the initiators [P. Rempp and cois, in Polymer Synthesis, Huthing and Wepf Verlag, Berlin, 1986]. Due to this it is necessary to consider some of the conditions necessary for a solvent to be used in this type of polymerizations: i) it must be aprotic to prevent any transfer or deactivation reaction, ii) it must be free of some electilic function, which can react with carbanionic sites. for example nitro groups, ester or ketone groups. The nature of the solvent is of great relevance, since for example the polymerization of butadiene, the use of a polar solvent has an effect on the microstructure of the polymer formed, since it favors the formation of a polymer with a high content of configuration l, 2 ( vinyl). The most used solvents in the anionic polymerization are cyclohexane, benzene, and tetrahydrofuranofR. P. Quirk et al., In Anionic Polymerization, Principies and Practical Applications, Marcel Dekker, New York, 1996]. Normal butyllithium (NBL) is used as an initiator, which is a very reactive compound, causing the butadiene molecules to react with each other to form a polybutadiene. For the reaction to start, the temperature must be 37 C p greater. Once the reaction begins, it will proceed quickly with the evolution of heat until essentially all of the monomer has adhered to the polymer chains, the resulting chain is able to continue to react as more monomer is added due to the terminal lithium reagent of the polymer. To prevent this, the "living" polymer is "finished" by the addition of a "short stop", which reacts with the lithium and gives rise to a j Reagent at end of the polymer chain. Each molecule of NBL will give a polymer chain unless there are traces of moisture, air or other poisons present in the reactor.

Ionic liquids in polymerization: i) Living anionic and ii) Ziegler-Natta In principle, LI's should be ideal solvents for anionic polymerization, due to their ability to stabilize anionic species. It has been found that ionic liquids provide an excellent medium for processes involving charged species [R. Vijayáraghavan and cois, in Chem.Commun. 2004, 700; R. Vijayáraghavan and cois, in Aust J Chem 2004, 57, 129]. For example, polymerization of styrene has been carried out satisfactorily at room temperature in an ionic liquid, providing more moderate reaction conditions than the classical methods. The addition of a zwitterionic species provides a better dissociation of the metallic cation (initiator) and the LI allows the use of a moderate Lewis base in comparison with those usually required [R. Vijayáraghavan et al, in Euan Polymer Journal, 2008, 44, 1758]. Polymerization by MMA coordination has been explored using a binary catalyst based on rare earths, neodymium versatate (NdV3) / Al (/ - Bu) 3, in LI's. It was found that the degree of polymerization of MMA increased and that the molecular weight of PMMA was higher in LI's than in toluene or in mass [Y. Xiong and cois, in Chemestry Letters, 2006,35,5] I BRIEF DESCRIPTION OF THE FIGURES Figure 1. Different possible microstructures in polybutadiene DETAILED DESCRIPTION OF THE INVENTION The patent revolves around a method of obtaining polydienes of the polybutadiene type, using both the anionic polymerization and Ziegler-Natta both in the presence of ionic liquids of the imidazolium type. As catalytic systems, n-butyl lithium was used for the case of anionic polymerization and the tertiary system versatato of neodymium (NdVVtri-isobutylaluminum (TIBA) / diethylaluminum chloride (DEAC) for Ziegler-Natta polymerizations) The polymerizations are preferably carried out in solution using cyclohexane in batch mode The reactor is initially charged with the solvent then added the monomer and the ionic liquid, and finally the respective catalytic system is added to start the polymerization, both anionic and Ziegler-Natta polymerizations are extremely exothermic, so that during the polymerization an increase in temperature takes place. However, the incorporation of ionic liquids decreases the maximum reaction temperature. On the other hand, the polymers resulting from both polymerizations in the absence of ionic liquids tend to show larger molecular weight distributions (MWD), compared to those obtained with ionic liquids. As for the microstructure, generally in Ziegler-Natta polymerizations without ionic liquids, a cis percentage greater than 90% is obtained. However, by the addition of the ionic liquid 1-ethyl-3-methylimidazolium chlorine [EMIM] [C1] the percentage can be modified to values of the order of 85% in cis microstructure. The recovery of ionic liquids is extremely simple, and these are not soluble in cyclohexane so that decantation is obtained most of the ionic liquid. The rest can be recovered with methanol.

EXAMPLES Anionic polymerization in the presence of ionic liquids Table 1 shows the recipes used in the ammonium polymerizations in presence of different ionic liquids.

Table 1. Recipes used in the anionic polymerization of butadiene in the presence of ionic liquids.

[B IM] [eS04]: l-butyl-3-methylimadazolium Methyl sulfate; [E I] [C1]: l-ethyl-3-methylimidazolium chloro; Ti "iciai: initial reaction temperature; in all polymerizations: cyclohexane: 1 .388 mol; n-butyl-lithium: 0.0016 mol: reaction time: 120 min The handling of the substances and the preparation of the initiation system will be carried out in inert atmosphere, using a glove box and using standard Schlenk techniques with a dual vacuum / argon system. The polymerizations were carried out in Parr reactors 1 L stainless steel fully conditioned to be loaded with butadiene and cyclohexane using additives developed in CIQA. For the polymerizations, the cyclohexane, the ionic liquid and the butadiene (in the amounts described in Table 1) were charged initially. The reactor was heated and once the desired temperature was reached, n-butyllithium was incorporated. The reaction was conducted until total conversion. Once all the monomer was consumed, the reaction was deactivated with iso-propanol and the antioxidant Irganox 1076 was added. The polymer was removed from the environment of the ionic liquid for further analysis.

Characterizations The polymers obtained were characterized by gel permeation chromatography (GPC), to know the distribution of molecular weights. Likewise, the temperature profile was obtained as a function of the reaction time.

Ziegler-Natta polymerization in the presence of ionic liquids Table 2 shows the recipes used in Ziegler-Natta polymerizations in the presence of different ionic liquids.

Table 2. Recipes used in the anionic polymerization of butadiene in the presence of ionic liquids.

[BMIM] [PF6]: l -butyl-3-methylaldazolium hexafluorophosphate; [BMIM] [BF4]: l-butyl-3-methylimidazole tetrafluoroborate; [EMIM] [Cl]: l-ethyl-3-methylimidazolium chloro; Ti icia): initial reaction temperature; Reaction time: 180 min. In all reactions: Neodymium versatate (NdV): 0.000476 f mole; tri-butylaluminum (TIBA): 0.010 mol; Diethylaluminum chloride (DEAC): 0.0014 mol; relation [Al] / [Nd]: 2 1; ratio [Cl] / d]: 3 The handling of the substances and the preparation of the initiation system will be carried out in an inert atmosphere, using a glove box and using standard Schlenk techniques with a dual vacuum / argon system. The polymerizations were carried out in 1L Parr stainless steel reactors fully conditioned to be loaded with butadiene and cyclohexane using additives developed in CIQA. For the polymerizations, the cyclohexane, the ionic liquid and the butadiene (in the amounts described in Table 2) were charged initially. The reactor was heated and once the desired temperature was reached, the previously aged tertiary type NdV / TIBA / DEAC catalytic system was incorporated. The reaction was conducted until total conversion and different samples were taken. Once all the monomer was consumed, the reaction was deactivated with iso-propanol and the Irganox 1076 antioxidant. The polymer was removed from the ionic liquid environment for further analysis.

Characterizations The polymers obtained were characterized by gel permeation chromatography (GPC), to know the distribution of molecular weights. Nuclear magnetic resonance of? to identify the microstructure. Differential scanning calorimetry to evaluate the thermal properties.

Results of the polymers obtained by anionic polymerization in the presence of ionic liquids Table 3 shows the results obtained from the characterization of the polybutadienes obtained by anionic polymerization.

Table 3. Characterization of the polybutadienes obtained via anionic polymerization Results of the polymers obtained by ZieglerNatta polymerization in the presence of ionic liquids Table 4 shows the results obtained from the characterization of the polybutadienes obtained by Ziegler-Natta polymerization Table 4. Characterization of the polybutadienes obtained via anionic polymerization

Claims (16)

CLAIMS Having sufficiently described the invention, the authors consider as a novelty, and therefore claim as their exclusive property, what is contained in the following clauses:

1. A method for carrying out polymerizations in living anionic solution comprising the steps of: a) Prepare in the reactor a solution of an organic solvent, an ionic liquid or a mixture of ionic liquids, and a diene monomer. b) Heat the reactor to the desired reaction temperature and add the catalyst to start the reaction. c) Separate the polymer at the end of the reaction

2. The method of claim 1, characterized in that said organic solvent is selected from a group consisting of non-polar organic compounds or mixtures thereof.

3. The method of claim 1, characterized in that said organic compounds are substances such as cyclohexane, hexane, toluene, etc. or mixtures thereof.

4. The method of claim 1, characterized in that said ionic liquid is selected from a group consisting of compounds such as those of the imidazolium, phosphonium, ammonium etc. type. or mixtures thereof.

5. The method of claim 1, characterized in that said diene monomer is selected from a group consisting of compounds such as butadiene, isoprene, etc. or mixtures thereof.

6. The method of claim 1, characterized in that said catalyst is selected from a group consisting of compounds such as n-butyl-lithium, s-butyl-lithium, etc. or mixtures thereof.

7. The method of claim 1, characterized in that during the polymerization reaction the increase in temperature is reduced between 5 and 26% compared to the polymerization reaction in which no ionic liquids are used.

8. The method of claim 1, characterized in that the polymer obtained has a polydispersion index between 4.7 and 8.5% lower than that of the polymer obtained in the polymerization in which no ionic liquids are used.

9. A method for carrying out polymerizations in solution via Ziegler-Natta polymerization comprising the steps of: a) Prepare in the reactor a solution of an organic solvent, an ionic liquid or a mixture of ionic liquids, and a diene monomer. b) Heat the reactor to the desired reaction temperature and add the catalytic system to start the reaction. c) Separate the polymer at the end of the reaction

10. The method of claim 9, characterized in that said organic solvent is selected from a group consisting of non-polar organic compounds or mixtures thereof.

1. The method of claim 9, characterized in that said organic compounds are substances such as cyclohexane, hexane, toluene, etc. or mixtures thereof.

12. The method of claim 9, characterized in that said ionic liquid is selected from a group consisting of compounds such as those of the imidazolium, phosphonium, ammonium type, etc. or mixtures thereof.

13. The method of claim 9, characterized in that said diene monomer is selected from a group consisting of compounds such as butadiene, isoprene, etc. or mixtures thereof.

14. The method of claim 9, characterized in that said catalyst system is selected from a group consisting of systems such as i) Neodymium versatate, triisobutylaluminum and diethylaluminum chloride, ii) ii) Neodymium versatate, diisobutylaluminum hydride and diethylaluminum, iii) Neodymium versatate, triethylaluminum and diethylaluminum chloride, etc. or mixtures thereof.

15. The method of claim 9, characterized in that during the polymerization reaction the increase in temperature is reduced between 6 and 100% compared to the polymerization reaction in which no ionic liquids are used.

16. The method of claim 9, characterized in that the polymer obtained has a polydispersion index between 27.6 and 55.5% lower than that of the polymer obtained in the polymerization in which no ionic liquids are used.