MXPA01011337A - An improved process for producing high molecular weight monovinylidene aromatic polymers and polymodal compositions - Google Patents

Abstract

The present invention is an improved process for producing high molecular weight monovinylidene aromatic polymers and polymodal compositions by free radical polymerization of a vinyl aromatic monomer in the presence of a vinyl acid, wherein the improvement comprises neutralizing the acid after production of the desired amount of high molecular weight monovinylidene aromatic polymer by adding a base.

Description

IMPROVED PROCESS TO PRODUCE AROMATIC POLYMERS OF MQNOVINYLIDENE OF MOLECULAR WEIGHT AND POLYMODAL COMPOSITIONS DESCRIPTION OF THE INVENTION The present invention relates to a process for producing high molecular weight monovinylidene aromatic polymers and polymodal molecular weight monovinylidene aromatic polymer compositions. Monovinylidene aromatic polymers of high weight average molecular weight (Mw) have previously been produced through free radical polymerization in the presence of a vinylic acid having a pKa of less than two as described in the US patent. .TO. 5, 145,924, and patent of E. U.A. 5,962,605 and patent of E. U.A. 5,948,874. Free radical polymerization is typically conducted in the presence of an initiator. However, it is well known in the art that at some point during polymerization, the initiator is depleted and thermal polymerization occurs unless an additional initiator is added. During the thermal polymerization of the vinyl aromatic monomer, conversion becomes difficult due to the presence of the acid and low molecular weight fractions are produced, as taught in J. Phys. Org. Chem. (1995) 8, p. 301. In addition, the presence of acid during thermal polymerization catalyzes the formation of 1-phenyltetralin, a by-product, as described in Polymer (1992) 33, p. 3055. At the high temperatures used to increase the conversion in the absence of the initiator, 1-phenyltetralin is formed rapidly in the presence of acid and must be removed from the polymer composition. Polymodal molecular weight monovinylidene aromatic polymer compositions, wherein the polymer composition comprises more than a different weight average molecular weight, have previously been produced in a number of ways, including in situ mixing and polymerization. The mixing of two polymers having different molecular weights offers a high degree of control, but is inefficient due to the addition of the combination step. The patent of E. U.A. No. 4,585,825 describes a bimodal composition, however, the high molecular weight polymer is produced at low temperatures and at low conversion rates, which require very long reaction times. The patent of E. U.A. 5,962,605 and patent of E. U.A. 5,948,874 disclose bimodal compositions produced using free radical polymerization, wherein the high molecular weight polymer is produced in the presence of a vinyl acid having a pKa of less than 2.0, and a low molecular weight polymer is produced by adding the initiator and a low molecular weight polymer. chain transfer to the reaction mixture containing the high molecular weight polymer. However, the presence of the vinyl acid delays the polymerization rate and continues to reinforce the production of high molecular weight polymer, thus requiring large amounts of chain transfer agent in order to produce the low molecular weight polymer. Therefore, it is highly desirable to provide an improved process for producing high molecular weight monovinylidene aromatic polymers, which does not require additional initiators, and reduces by-product formation; and to provide an improved process for producing polymodal compositions, comprising such high molecular weight polymers, which does not require large amounts of chain transfer agents in order to make a low molecular weight polymer. The present invention is an improved process for producing a high molecular weight monovinylidene aromatic polymer, wherein an aromatic vinyl monomer is radically polymerized in free form in the presence of a vinyl acid having a pKa at 25 ° C lower than 2.0, in where the improvement comprises: Neutralizing the acid, after the production of the desired amount of the high molecular weight polymer, with a sufficient amount of base, so that substantially all of the acid is neutralized, and the free radical polymerization continues in the absence of the acid, under conditions such that an aromatic monovinylidene polymer is produced at the additional high molecular weight. In another embodiment, the present invention is an improved process for producing molecular weight monovinylidene aromatic polymer polymodal compositions, wherein an aromatic vinyl monomer is radically polymerized in free form in the presence of an acid having a pKa at 25 ° C lower 2.0, to produce a high molecular weight monovinylidene aromatic polymer and a low molecular weight monovinylidene aromatic polymer is produced in a subsequent step, wherein the improvement comprises: Neutralizing the acid, after production of the desired amount of the high molecular weight polymer, with a sufficient amount of a base, so that substantially all of the acid is neutralized, and continuing the polymerization of free radical in the absence of the acid, under conditions so that a monovinylidene aromatic polymer is produced having a low molecular weight. This process can produce high molecular weight monovinylidene polymers with high conversion without the formation of important sub-products or low molecular weight fractions. It also offers better control of the molecular weights of the polymer within the bimodal composition and does not have the disadvantages of the prior art. Monovinylidene aromatic polymers can be produced through the free radical polymerization of vinyl aromatic monomers. The vinyl aromatic monomers to be used in accordance with the present invention include, but are not limited to, those vinyl aromatic monomers previously known for use in polymerization processes, such as those illustrated in the patent of US Pat. 4,666,987, U.A. 4,572,819 and patent of E. U.A. 4,585,825. Preferably, the monomer is of the formula: R Ar- C- CH: wherein R is hydrogen or methyl, Ar is phenyl, halophenyl, alkylphenyl or alkylhaphenyl, wherein any alkyl group contains from 1 to 6 carbon atoms. The term "halophenyl" refers to a phenyl substituted with one or two halogen atoms, the term "alkylphenyl" refers to a phenyl substituted with one or two alkyl groups, and the term "alkylhaphenyl" refers to phenyl substituted with 1 or 2 alkyl groups, which contain a halogen substituent or a phenyl substituted with a halogen and with an alkyl substituent. Most preferably, Ar is phenyl or aikilphenyl, with phenyl being very preferred. In addition, the polymerization can be conducted in the presence of predisposed elastomer to prepare products containing modified or grafted rubber, examples of which are described in the patent of E. U.A. 3, 123, 655, patent of E. U.A. 3,346,520, patent of E. U.A. 3,639,522, and patent of E. U.A. 4,409,369. The acid catalyst used in the process of the present invention can be any acid having a pKa at 25 ° C less than 2. The pKa is used to express the degree of dissociation of acids in water, and is the negative logarithm (a the base 10) of the equilibrium constant, Ka. Such acid catalysts include, but are not limited to, 2-sulfoethylmethacrylate (SEM), acrylamidopropanesulfonic acid (AMPS), 2-sulfopropylmethacrylate, methanesulfonic acid, camphorsulfonic acid, p-toluenesulfonic acid, phosphoric acid, sulfuric acid, or mixtures thereof. same. Preferably, the acid catalyst is a vinyl functional sulfonic acid or vinyl functional phosphonic acid of the formulas: where X is O and n is either 0 or 1; And it is H, methyl or phenyl; Z is d-C6 alkyl, aryl or O-Y; and R is -C (= O) OCH2CH (Y) -, -C (= O) NHCH2CH (Y) -, phenyl or a direct bond. Examples of such acids include 2-sulfoethylmethacrylate (SEM), acrylamidopropane sulfonic acid, vinylphosphonic acid (VPA), 2-sulfopropylmethacrylate (SPM), styrenesulfonic acid (SSA), styrene phosphonic acid (SPA), 4-vinylbenzylphosphonic acid (VBPA), 2 sulfoethylacrylate (SEA), a-phenylvinylphosphonic acid (PVPA), or mixtures thereof, the highly preferred vinyl acid being SEM. These acids are known and commercially available or can be made through the processes described in US Pat. 4, 529,559. The acid catalyst can be dispersed in (meth) acrylic acid or its ester, before being combined with the aromatic vinyl monomer. The term (meth) acrylic acid refers to either a methacrylic acid or an acrylic acid. An ester of (meth) acrylic acid can be any d-C8 ester of methacrylic acid or acrylic acid. Accordingly, through the application, any teaching referring to (meth) acrylic acid can also be applied to an ester thereof. The (meth) acrylic acid acts as a reactive dispersant, copolymerizing in the aromatic vinyl polymer chain during the polymerization, so as not to contaminate the polymer or the volatile recirculation stream. The (meth) acrylic acid also serves as a pH regulator for very strong acid catalysts. Since styrene can be added without initiating cationic polymerization. The acid catalyst generally comprises from 0.1 to 75% by weight of a mixture of acid / acid (meth) acrylic catalyst typically 0.5, preferably 1, preferably 5, and most preferably 10 to 75, typically 70, preferably 65, preferably at 60 and most preferably at 50% by weight of the acid / acid (meth) acrylic catalyst mixture. The amount of the acid / acid (meth) acrylic catalyst mixture present in the polymerization depends on the concentration of the acid catalyst in the mixture. Typically, the acid catalyst is present in the polymerization in amounts such that a high molecular weight polymer is produced without appreciably and adversely affecting the properties of the polymer. The amount of the acid catalyst needed will depend on the particular acid catalyst used. It has been found that good results are obtained when the ratio (pKa X molecular weight of acid catalyst) / (concentration of the acid catalyst in ppm based on aromatic vinyl monomer) is 0.01, preferably 0.05, preferably 0.08 to 1, most preferably 0.5, and preferably 0.3. In the case of acid salts, this could be based on the pKa of the acid component of the salt. In general, acid catalysts with higher pKa values will be present in larger amounts than acid catalysts with lower pKa values. Generally, the acid catalyst will be present in an amount of 1, typically 5, preferably 10, preferably 15, and most preferably 25 ppm to 1000, typically 950, preferably 900, preferably 850, and most preferably at 800 ppm, based on the amount of vinyl aromatic monomer. Vinyl acids containing sulfur can be used in amounts that will produce a high molecular weight polymer without initiating the cationic polymerization. If the amount of sulfur containing vinyl acids is too large, the acid will initiate cationic polymerization, which will produce low molecular weight polymers, for example, less than 20,000 Mw. The cationic polymerization can therefore be detected by the formation of low molecular weight fractions within the high molecular weight polymer produced. Typically, amounts of 1, preferably 5, preferably 10, most preferably 15 to 500 ppm, preferably 400, preferably 300 and most preferably 100 ppm of a sulfur containing vinyl acid are present, based on the amount of the vinyl aromatic monomer. Vinyl acids containing phosphorus may be present in larger amounts and are not known to initiate cationic polymerization. Typically, amounts of from 500 to 20,000 ppm of the phosphorus-containing vinyl acid are present, preferably from 600 to 15,000, preferably from 800 to 10,000 and most preferably from 1,000 to 5,000 ppm based on the amount of the vinyl aromatic monomer. Free radical polymerization to produce a monovinylidene aromatic polymer of high molecular weight can optionally be conducted in the presence of a stable free radical compound, nitroxyl, as described in "Narrow Polydispersity Polystyrene by a Free-Radical Polymerization Process-Rate Enhancement ", Macromolecules 1994, 27, p. 7228-7229. Typical nitroxyl radical compounds include 2,2,6,6-tetramethyl-1-piperidinyloxy and 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxy. Typical amounts of stable nitroxyl free radical are from 10 ppm, to 2, 000 ppm based on the amount of the vinyl aromatic monomer.

A free radical initiator can be used in free radical polymerization to produce the high molecular weight polymer. Typical initiators include azo compounds and peroxides. Illustrative peroxides include tert-butyl peroxybenzoate, tert-butyl peroxyoctoate, di-tert-butyl peroxide, dibenzoyl peroxide, dilauroyl peroxide, 1,1-bis-tert-peroxycyclohexane, 1,1-bis-ter buty-peroxy-3, 3,5-trimethylcyclohexane and dicumyl peroxide. In addition, a solvent can be used in the process of the present invention. Representative solvents include substituted aromatic and aromatic hydrocarbons, such as benzene, ethylbenzene, toluene, xylene, or the like; saturated saturated straight or branched chain aliphatics substituted or unsubstituted of 5 or more carbon atoms, such as heptane, hexane, octane, or the like; substituted alicyclic or alicyclic hydrocarbons having 5 or 6 carbon atoms, such as cyclohexane; and similar. Preferred solvents include substituted aromatics, with ethylbenzene, toluene and xylene being most preferred. If employed, the solvent is generally employed in an amount of up to 35% by weight, preferably 2 to 25% by weight, based on the total weight of the solution. The polymerization can be conducted at any temperature at which a high molecular weight polymer will be produced. Suitable polymerization temperatures are from 80 to 170 ° C, preferably from 10 ° C to 160 ° C, 115 to 150 ° C being most preferred.

Once the desired level of high molecular weight polymer is achieved, a base is added to the reaction mixture of the monovinylidene aromatic polymer of high molecular weight and unreacted monomers and other optional components. Typically, the base is added at a vinyl aromatic monomer conversion level of 20 to 60%, preferably between 25 and 55 and most preferably between 30 and 50%. Preferably, the base is a material that readily dissolves in the aromatic vinyl monomer or organic solvent, or can sufficiently be dispersed and / or emulsified within a vinyl aromatic monomer, so that neutralization of the vinyl aromatic monomer can be achieved. acid. Useful bases for the present invention include any base that will neutralize the acid catalyst used. Typical bases include metal salts such as zinc stearate, calcium stearate and sodium stearate, amines such as trioctylamine, imidazolenes such as faurylimidazolene, and ammonia. The amount of base added is typically at least one molar equivalent to the amount of acid present in the polymerization. In other words, at least one mole of base is added per mole of acid present. Generally, an excess is added in order to reduce the amount of time required for total neutralization. Preferably, at least 1.2 molar equivalents of the base are added, preferably at least 1.25 and most preferably at least 1.3 molar equivalents. The. The base can be added in any form, which will properly neutralize the acid after the addition to the polymerization reaction. Typical forms include net liquid, gas, hot melt bath, an aromatic monovinylidene polymer solution or organic solvent, a slurry, dispersion or emulsion. In one embodiment, the base is added as a base slurry, monovinylidene aromatic polymer and solvent. After addition of the base, the polymerization is thermally continued to produce an additional high molecular weight monovinylidene aromatic polymer. The thermal polymerization is typically conducted at a higher temperature in order to increase the polymerization rate. Typically, the temperature for thermal polymerization will be between 140 and 170 ° C. This process produces a monomodal aromatic polymer of monovinylidene of high molecular weight. Monomodal refers to the weight average molecular weight distribution of the polymer having a different weight average molecular weight peak when evaluating different conversion fractions of the polymer produced, but does not necessarily refer to a polymer that has a polydispersity of 1. The Mw of the monomodal polymer will typically be from 250,000 to 400,000, preferably from 250,000 to 350,000, preferably from 250,000 to 330,000 and most preferably 300,000 to 330,000. The Mw defined within the present specification refers to an Mw measured using gel permeation chromatography (GPC). In another aspect of the present invention, an aromatic monovinylidene polymer of low molecular weight is produced after the high molecular weight polymer, in order to produce a polymodal composition. A polymodal composition refers to the weight average molecular weight distribution of polymer having more than one different weight average molecular weight peak when different conversion fractions of the produced polymer are evaluated. In this process, the base is added to the polymerization reaction once the desired level of monovinylidene aromatic polymer of high molecular weight is produced. Typically, the base is added at a vinyl aromatic monomer conversion level of 20 to 60%, preferably between 25 and 55 and most preferably between 30 and 50%. After neutralization with acid, the polymerization is continued under conditions such that a low molecular weight polymer is produced. This is achieved through various methods known to those skilled in the art, including temperature control and use of chain transfer agents and / or primers. If an initiator is used to produce the low molecular weight polymer, the initiator can be any initiator or mixture of initiators, which polymerize the unreacted monomer in the mixture containing the high molecular weight polymer. The initiator can be any free radical initiator as discussed previously, and is preferably a peroxide initiator such as tert-butyl peroxybenzoate, tert-butyl peroxyoctoate, di-tert-butyl peroxide, dibenzoyl peroxide, peroxide dilauroyl, 1,1-bis-tert-butyl peroxycyclohexane, 1-bis-tert-butylperoxy-3,3,5-trimethylcyclohexane and dicumyl peroxide. Typical amounts of 10 ppm to 2,000 ppm, based on the amount of the vinyl aromatic monomer.

Optionally, chain transfer agents can be used in the preparation of the low molecular weight polymer. Suitable chain transfer agents include common chain transfer agents known in the art such as mercaptans. Preferably, the chain transfer agent is n-dodecyl mercaptan or terpinoline. Typical amounts of chain transfer agents are from 10 ppm to 4,000 ppm, based on the amount of the vinyl aromatic monomer. The molecular weight of the high molecular weight polymer can be selected according to the desired Mw of the polymodal composition and preferably is from 300,000 to 2,000,000, preferably from 350,000 to 1,500,000 and most preferably from 400,000 to 800,000. The desired Mw of the low molecular weight polymer is also a selection material and depends on the desired Mw of the bimodal composition and the desired properties. Preferably, the Mw is 50,000 to 200,000. The amount of high molecular weight polymer present in the polymodal composition can be selected according to the desired properties of the polymodal composition. Typically, of 1 to 99%, preferably from 5 to 55% and most preferably from 10 to % of the high molecular weight polymer is present. The average Mw of the polymodal compositions depends on the Mw of the polymers contained within the composition. The average Mw of the bimodal composition of this embodiment of the present invention is preferably from 120,000 to 600,000, preferably from 130,000 to 500,000 and most preferably from 140,000 to 400,000. The composition containing both high and low molecular weight vinyl aromatic polymers can be any combination of two vinyl aromatic polymers, but preferably it is a polymer blend having the same composition (ie, homopolymers of the same monomer units or copolymers having the same comonomer units in similar ratios). Most preferably, both polymers are polystyrene. A preferred process for the production of the bimodal composition is a continuous polymerization process, wherein a group of several different reaction zones within one or more reactors are used in series to create the polymers of different molecular weight. The different zones are maintained at the desired temperatures and supplied with appropriate reagents necessary to produce the desired amounts of polymer having the specified molecular weights, so that polymodal compositions are produced. In a preferred process, an early polymerization zone is maintained, so that a high molecular weight polymer is produced, while a subsequent zone receives the reaction mixture from the previous zone, including the high molecular weight polymer, and is supplied with the base to neutralize the acid. This latter zone is supplied with additional reagents, including an initiator and / or a chain transfer agent, and is otherwise maintained so as to produce a low molecular weight polymer in the presence of the previously produced high molecular weight polymer, a mixture of the two components being obtained in this way. Usually, the early high molecular weight polymer production reactor or zone is at a lower temperature than the subsequent low molecular weight polymer production reactor or zone. The bimodal compositions containing polymers of high molecular weight and low molecular weight are useful for a variety of applications including foam board, foam sheet, injection molding and extrusion. Other traditional polymer additives may be included in the process of the present invention, including plasticizers and mold release agents. The following examples are provided to illustrate the present invention. The examples are not intended to limit the scope of the present invention and should not be so interpreted. The amounts are in parts by weight or percentages by weight unless otherwise indicated.

EXAMPLE 1 A 2.5 liter polymerization vessel equipped with an overhead stirrer, an addition vessel, and a nitrogen inlet was charged with 1425 grams of styrene monomer, 75 grams of ethylbenzene and 0.0075 grams of a 50/50 mixture. of sulfoethylmethacrylate (SEM) / methacrylic acid (MAA). The reactor is pressurized to 2-3 bars of gauge and the following temperature profile was used for the polymerization: Samples were taken at 2, 4 and 5 hours and were measured for percent solids (conversion) and molecular weight, using gel permeation chromatography (GPC). Zinc stearate was added as a slurry of 9.5% polystyrene, 5% by weight zinc stearate, and 85.5% by weight of ethylbenzene in an amount of 933 ppm zinc stearate, based on the total weight of the mixture. reaction in operations 2-4. (An excess of zinc stearate is used because of its additional function as a mold release agent). Operation 1 was completed without any base addition to the polymerization reaction. Operation 2 was completed with the addition of zinc stearate to the original reagent feed.

Operation 3 was completed with the addition of zinc stearate after 2 hours of polymerization. Operation 4 was completed with the addition of zinc stearate after 2.5 hours of polymerization, at a level of 100 ppm zinc stearate based on the total weight of the reaction mixture. Operation 5 was completed with the addition of trioctylamine after 2.5 hours of polymerization, at a level of 550 ppm based on the total weight of the reaction mixture. Operation 6 was completed with the addition of laurylimidazolene after 2.5 hours of polymerization, at a level of 2000 ppm based on the total weight of the reaction mixture. Operation 7 was completed with the addition of a 0.5% solution of ammonia in ethylbenzene after 2.5 hours of polymerization, at a level of 25 ppm of ammonia based on the total weight of the reaction mixture. The results are listed in Table I I.

Table II * Comparative Examples Operation 1 is a comparative example to show a polymerization without the neutralization of vinyl acid, where only a high Mw polymer is obtained. The operation 2 is a comparative example to show a polymerization the effect on the Mw when the base is present from the beginning of the polymerization. No high Mw polymer is obtained. Steps 3-7 are examples for producing bimodal Mw compositions by neutralizing the vinyl acid after having produced a high Mw polymer, and wherein the low Mw polymer is subsequently produced.

Claims (10)

1. - An improved process for producing a high molecular weight monovinylidene aromatic polymer, wherein an aromatic vinyl monomer is radically polymerized in free form in the presence of an acid to obtain a pKa at 25 ° C less than 2.0, wherein the improvement comprises : neutralizing the acid, then producing the desired amount of high molecular weight polymer, with a sufficient amount of base, so that substantially all of the acid is neutralized, and continuing the polymerization of free radical in the absence of the acid, under conditions so that an additional high molecular weight monovinylidene aromatic polymer is produced.

2. An improved process for producing polymodal molecular weight monovinylidene aromatic polymer compositions, wherein an aromatic vinyl monomer is radically polymerized in free form in the presence of a vinyl acid obtaining a pKa at 25 ° C lower than 2.0, for producing a monoviniiidene aromatic polymer of high molecular weight and a monovinylidene aromatic polymer of low molecular weight is produced in a subsequent step, wherein the improvement comprises: neutralizing the acid, then producing the desired amount of high molecular weight polymer , with a sufficient amount of base, so that substantially all of the acid is neutralized, and the free radical polymerization continued in the absence of the acid, under conditions such that a monovinylidene aromatic polymer having a low molecular weight is produced.

3. The process according to claim 1 or 2, wherein the acid catalyst is a vinyl functional or phosphonic vinyl functional sulfonic acid, of the formula: where X is O and n is either 0 or 1; And it is H, methyl or phenyl; Z is C1-C6 alkyl, aryl or O-Y; and R is -C (= O) CH 2 CH (Y) -, -C (= O) N HCH 2 CH (Y) -, phenyl or a direct bond.

4. The process according to claim 1 or 2, wherein the acid is 2-sulfoethylmethacrylate, acrylamidopropanesulfonic acid, 2-sulfopropylmethacrylate, styrenesulfonic acid or 2-sulfatoethylmethacrylate.

5. The process according to claim 1 or 2, wherein the vinyl aromatic monomer is styrene.

6. The process according to claim 1 or 2, wherein the base is selected from the group consisting of zinc stearate, calcium stearate, sodium stearate, trioctylamine, laurylimidazolene and ammonia.

7. - The process according to claim 1 or 2, wherein the base is added in an amount of at least 1 molar equivalent to the amount of acid.

8. The process according to claim 2, wherein the high molecular weight vinyl aromatic polymer and the low molecular weight vinyl aromatic polymer are both polystyrene.

9. The process according to claim 8, wherein the high molecular weight polystyrene has an Mw of 500,000 to 2,000,000 and the low molecular weight polystyrene has an Mw of 50,000 to 200,000.

10. The process according to claim 2, wherein the low Mw polymer is produced in the presence of a chain transfer agent. 1. The process according to claim 10, wherein the chain transfer agent is n-dodecyl mercaptan.