FR2726827A1 - PROCESS FOR THE PREPARATION OF COPOLYMERS OF ALKYL METHACRYLATE - Google Patents

Abstract

The invention relates to a process for the preparation of copolymers by mass polymerization of monomer mixtures consisting of m1) from 50 to 90% by weight of C1 -C6 alkyl methacrylate, (m2) from 5 to 25% by weight d 'at least one vinyl aromatic compound, (m3) from 1 to 25% by weight of maleic anhydride and optionally (m4) from 0 to 5% by weight of C1 -C6 alkyl acrylate, the sum of the units (m1 ), (m2), (m3) and optionally (m4) being equal to 100% by weight, in the presence of polymerization initiators and molecular weight regulators, maleic anhydride (m3) being added in the physical state liquid to other monomers, before polymerization. Preferably, mixtures of the units (m1) / (m3) are prepared in weight ratios of between 75/1 and 75/25 which are added to the other units (m2) and optionally (m4). Preference is given to methyl methacrylate as component (m1) and to styrene and / or alpha-methylstyrene as component (m2).

Description

The invention relates to the preparation of copolymers consisting of

  monomer units alkyl methacrylate, vinylaromatic compound and maleic anhydride, a process in which, in a step preceding the polymerization of the monomers, maleic anhydride is incorporated by mixing, in the liquid state, in liquid alkyl methacrylate or in the liquid mixture of alkyl methacrylate and

vinylaromatic compound.

  Copolymers consisting of monomeric units of alkyl methacrylate, vinylaromatic compound and maleic anhydride and processes for their preparation are known. Thus, it is described in DE-OS 12 31 013 a process for the preparation of copolymers by

  mass polymerization from 1 to 50% by weight of

  alkylstyrene and from 99 to 50% by weight of alkyl methacrylate with minor amounts of one or more other polymerizable compounds, in the presence of polymerization catalysts, 0.1 to 20% by weight of maleic anhydride and / or of methacrylic acid, based on the total monomer mixture, being used as other polymerizable compounds. The addition of maleic anhydride or methacrylic acid has the effect of significantly shortening the polymerization times of mixtures of alkyl methacrylate and α-alkylstyrene

  Until the complete transformation of the monomers.

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  No. 3,336,267 relates to a process for the preparation of copolymers composed of 5 to 95 mol% of a vinylaromatic compound, 5 to 40 mol% of a cyclic anhydride α, β-unsaturated, as well as from 0 to 90 mol% of a C 1 -C 4 alkyl (meth) acrylate, a mixture of these monomers being polymerized continuously, in the presence of an inert solvent, and the polymer being

  continuously extracting the reaction mixture.

  It is claimed in EP-A 113 105 for the preparation of dimensionally stable hot molding compositions, a process in which a mixture of a copolymer I, consisting of methyl methacrylate, a vinylaromatic compound is produced. and maleic anhydride, and a copolymer II, composed of methyl methacrylate and other copolymerizable monomers. Polymer blends

are colorless and transparent.

  EP-A 264 590 describes, for the preparation of a mass to be molded from a mixture of monomers composed of methyl methacrylate, a vinylaromatic compound, maleic anhydride and optionally an alkyl acrylate lower, a process in which the polymerization is carried out to a degree of conversion of 50% in the presence or absence of a non-polymerizable organic solvent, and in which the polymerization is continued, from a degree of transformation by at least 50%, in the temperature range of 75 to 150 ° C in the presence of an organic solvent Up to a degree of conversion of at least 80%, then the volatile constituents of low weight

molecular are evaporated.

  In JP-A 60-147 417, a process is described in which a monomer mixture of methyl methacrylate, maleic anhydride and a mixture of monomers consisting of methyl methacrylate, maleic anhydride and a methacrylic molding compound of high dimensional stability with heat is produced. at least one compound

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  Vinylaromatic is introduced and polymerized at a temperature of 100 to 180 ° C in a polymerization reactor suitable for solution or bulk polymerization. The resulting polymers are from 35 to 98% by weight of methyl methacrylate, from 1 to 35% by weight of vinyl aromatic compound and from 1 to 40% by weight of maleic anhydride, having intrinsic viscosities.

between 35 and 350 ml.

  As pointed out in US Pat. No. 3,336,267, α,--unsaturated cyclic acid anhydrides are solids and are only poorly soluble in the other monomers. This is particularly true for maleic anhydride. In the processes of the state of the art, efforts are made to solve this problem by the addition, before or during the polymerization, of

  inert solvents with regard to the polymerization.

  The choice of appropriate solvents is difficult and must

  be adapted exactly to the polymerization conditions.

  In addition, the solvent must be removed after completion of the polymerization, optionally treated by distillation and returned to the polymerization process. The object of the invention is therefore to provide, for the preparation of copolymers containing maleic anhydride with alkyl methacrylates and vinylaromatic compounds as other monomeric units, a process in which it is not used to solvent and in which the maleic anhydride is dissolved completely and rapidly in the others

monomers.

  It has surprisingly been found that this object is achieved remarkably by the addition of liquid maleic anhydride to alkyl methacrylate or to the mixture of alkyl methacrylate and vinylaromatic compound

before the polymerization.

  As a result, according to the invention, there is provided a process for the preparation of CP copolymers by bulk polymerization of monomer mixtures consisting of the following monomeric units: (ml) 50 to 90% by weight of alkyl methacrylate containing 1 to 6 carbon atoms in the ester residue,

  (m2) 5 to 25% by weight of at least one vinylaromatic compound

tick,

  (m3) 1 to 25% by weight of maleic anhydride and optionally

  (m4) 0 to 5% by weight of alkyl acrylate containing 1 to 6 carbon atoms in the ester residue, the sum of (ml), <m2), (m3) and optionally (m4) being equal to 100% by weight, characterized in that before the polymerization, maleic anhydride (m 3) is added and mixed, in the liquid physical state, with the monomer (ml) or the monomer mixture (ml), (m 2) and optionally (m4>.) Maleic anhydride (m 3) is preferably added and mixed at a temperature of between 55 ° C. and 80 ° C., and particularly preferably under an inert gas atmosphere. the invention, maleic anhydride (m3) is premixed with alkyl methacrylate (ml) in weight ratios (ml) / <m3) of 75/1 to 75/25 parts by weight, the mixture is optionally stored and it is added and mixed, before the polymerization, with

  remaining monomers (m2) and possibly (m4).

  It is particularly preferable to use, as the monomer component (ml), methyl methacrylate in amounts of 60 to 85% by weight based on the monomer mixture. In addition, it is particularly preferable that the monomer component (m2) is

  styrene and / or α-methylstyrene.

  Advantageously, the polymerization adjuvants, such as the polymerization initiator PI and the molecular weight regulator MR, are added only after the preparation of the monomer mixture, generally shortly before the start of the polymerization. Monomers (ml), (m2), (m3) and (m4) The monomers (ml), used in a proportion of 50 to 90% by weight relative to the total monomers, are chosen from the group of alkyl methacrylates containing 1-6 carbon atoms in the ester residue, such as, for example, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate,

  isobutyl methacrylate, methacrylate of tert.

  butyl, pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, 2,2-dimethylbutyl methacrylate, cyclopentyl methacrylate, cyclohexyl methacrylate and, with a preference

  particular, methyl methacrylate.

  The monomers (m 2) are selected from the group of

  vinylaromatic compounds, such as, for example,

  halostyrenes, p-methylstyrene, p-tert.-

  butylstyrene, vinylnaphthalene, preferably

  methylstyrene and, with particular preference, the

styrene.

  Maleic anhydride monomer (m 3) is used with a purity of at least 95%, preferably at least 99%. In order to bring the maleic anhydride into the liquid physical state, it is heated above its melting point of 52.85 ° C, at temperatures preferably between 55 and 80 ° C, and with particular preference between 60 and 80 ° C. Liquid maleic anhydride can be stored at these temperatures for

  several weeks under an inert gas atmosphere.

  The alkyl acrylates (m4) can be incorporated in amounts of up to 5% by weight in order to improve the rheological properties of the TP terpolymers. Examples of alkyl acrylates containing from 1 to 6 carbon atoms in the ester residue are ethyl acrylate, isopropyl acrylate, propyl acrylate and isobutyl acrylate. tert.-butyl acrylate, pentyl acrylate, hexyl acrylate, preferably butyl acrylate and, with a preference

  particular, methyl acrylate.

  Monomers (ml), (m2) and <m4) or mixtures thereof

  are liquid under the conditions of the mixture.

  The polymerization process In the first step of the polymerization process according to the invention, maleic anhydride (m 3) is added and mixed, in the liquid physical state, with the mixture of the other monomers, also liquid, or, preferably, it is first added and mixed with the liquid monomer (ml). The monomer mixtures are prepared by stirring in heatable tanks, such as

  example that tanks with a stirrer.

  Preferably, the liquid maleic anhydride (m 3) is first mixed with the liquid monomer (ml) in weight ratios (ml) / (m 3) of between 75/1 and 75/25 parts by weight and, with particular preference between 75/5 and 75/20 parts by weight. Preferably, the maleic anhydride maintained at a constant temperature of 55 to 80 ° C is stirred into the liquid alkyl methacrylate (ml), which may generally be at 0 to 60 ° C. The resulting monomer mixtures are clear and storage stable at room temperature for several months without the maleic anhydride separating to the crystalline state. As an upper limit for the proportion of (m3) in storage stable blends (ml) / (m3) at room temperature, the 75/30 weight ratio can be considered. In order to ensure storage stability at lower temperatures, for example at C, the maleic anhydride content in the mixtures (ml) / (m 3) must be reduced to ratios of

  between 75/1 and 75/15 parts by weight.

  Shortly before the start of the polymerization, the mixture of (ml) and (m3) thus obtained is added and mixed with the monomers (m2) and optionally (m4), the addition of the monomers (m2) and (m4) to the mixture of (ml) / (m3) being also possible. In general, the addition of the polymerization adjuvants, such as PI polymerization initiators and MR molecular weight regulators, is carried out in parallel with the addition of the monomers (m 2) and (m 4), but the polymerization adjuvants can be also added in a later step. In another embodiment of the invention, liquid maleic anhydride is incorporated directly, with stirring, in the liquid mixture of the other monomers (ml), (m2) and optionally (m4). The mixing ratios (ml) + (m2) + (m4) to (m3) are generally between 75/1 and 75/25 parts by weight, preferably between 75/5 and 75/20 parts by weight, the mixtures being also storage stable in the absence of oxygen. Again, the temperature of liquid maleic anhydride (m 3) is preferably between 55 and 80 ° C and, most preferably, between 55 and 65 ° C, while the liquid mixture of the other monomers generally has temperatures between 0 and 60 ° C. As a general rule, the polymerization adjuvants, such as in particular the PI polymerization initiators and the MR molecular weight regulators, are added to the mixture of the monomers (ml), (m2) and optionally (m4) before the addition of the monomers. maleic anhydride (m3). In certain embodiments of the invention, the polymerization adjuvants may also be added.

  after the addition of maleic anhydride (m3).

  It is advantageous to begin the polymerization of the monomers immediately after the addition of the anhydride

  maleic or polymerization adjuvants.

  The addition of the maleic anhydride (m 3) to the monomer (ml) or to the monomer mixture m 1), (m 2) and optionally (m 4) is advantageously carried out in the absence of oxygen from the air, which can be removed for example by applying a vacuum or by scanning with inert gases, such as nitrogen or argon, to avoid side reactions of maleic anhydride. The TP terpolymers are prepared by the known processes for mass polymerization of α, β-unsaturated compounds, in particular by radical polymerization. The polymerization is triggered in a manner known per se by PI polymerization initiators forming radicals, but it can also be conducted in a purely thermal manner, with a lower rate of polymerization. As a rule, a single addition of the polymerization initiator PI is sufficient before the start of the polymerization, the polymerization initiator PI being chosen so that sufficient radical formation occurs under the polymerization conditions. Until the end of it. Examples of polymerization initiators PI are:

  azo compounds such as 2,2'-azobis

  (isobutyronitrile) or - 2,2'-azobis (2,4-

  dimethylvaleronitrile), redox systems such as for example the combination of tertiary amines with peroxides or, preferably, peroxides (see for example in this respect H. Rauch-Puntigam, Th. Volker, "Acryl- und Methacrylverbindungen" , Springer, Heidelberg, 1967 or Kirk-Othmer, Encyclopedia of Chemical Technology, Vol 1, pp. 386 et seq., J. Wiley, New York, 1978. Examples of initiators are:

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  Suitable peroxide polymerization polymers are dilauroyl peroxide, tert-butyl peroctanoate, tert-butyl perisononanoate, dicyclohexyl peroxydicarbonate or dibenzoyl peroxide. The polymerization can also be carried out with a mixture of different polymerization initiators having different half-life periods, for example

  dilauroyl peroxide and perisononanoate of tert.-

  butyl, in order to keep the radical flow constant during the polymerization and at different polymerization temperatures. The amounts used of PI polymerization initiator are generally between 0.01 and 2% by weight relative to the mixture

of monomers.

  The adjustment of the molecular weights of the copolymers CP is carried out by polymerization of the monomer mixture in the presence of molecular weight regulators XR, such as in particular the mercaptans known for this purpose,

  for example n-butyl mercaptan or n-

  dodecylmercaptan, the molecular weight regulators being used in general in proportions of 0.05 to% by weight relative to the monomer mixture, preferably in proportions of 0.1 to 2% by weight and, with particular preference, in proportions of 0, 2 to 1% by weight relative to the monomer mixture

  (see for example H. Rauch-Puntigam, Th. Volker, "Acryl-

  und Xethacrylverbindungen ", Springer, Heidelberg 1967, Houben-Weyl, Methoden der organischen Chemie, vol.

  XIV / 1, page 66, Georg Thieme, Heidelberg, 1961 or Kirk-

  Othmer, Encyclopedia of Chemical Technology, vol. 1, pp. 296 et seq., J. Wiley, New York, 1978). The average molecular weights M. thus adjusted of the CP copolymers are generally between 101 and 5 × 10 5 daltons, preferably between 3 × 10 4 and 2.5 × 10 5 daltons, which corresponds to reduced viscosities n, p & c / C, measured in accordance with DIN 51 562 in chloroform, from 10 to 10 g / l, preferably from 15 to 100 g / ml, relative to polymethyl methacrylate as a standard standard (for the determination of Molecular average M-, see for example HF Mark et al., Encyclopedia of Chemical Science and Technology,

  flight. 10, pp. 1-19, J. Wiley, New York, 1978).

  In addition, monomer mixtures M may contain, in addition to PI polymerization initiators and MR molecular weight regulators, other additives, such as, for example, UV absorbers, antioxidants, dyes or pigments, as well as demolding auxiliaries, in amounts of up to 10% by weight relative to the monomers reacted. Preparation of the copolymers CP from the monomer mixtures is preferably carried out by bulk polymerization, in particular in polymerization chambers. appropriate of conventional type. In general, during the polymerization, the polymerization chambers are maintained at constant temperatures of 20 to 100 ° C in a water bath and / or 20 to C in a stream of air, in order to maintain a steady stream of radicals from the decomposition of the polymerization initiator. After completion of the polymerization, which is conducted to monomer conversion levels of at least%, preferably at least 97%, the CP copolymer is discharged from the polymerization chamber in the form of a block, crushed and subjected to an extrusion of degassing, followed by granulation. The resulting CP copolymer granulate is very transparent, colorless and generally has residual monomer contents of less than 2% by weight relative to

to the monomers reacted.

  The copolymers CP may be converted, for example thermoplastically, in the absence of dyes or pigments, into colorless transparent molded molds having Vicat VET softening temperatures, according to DIN 53460,

  from about 100 to 160 ° C, preferably from 120 to 150 ° C.

  Advantageous Effects of the Invention Manipulation of maleic anhydride (m 3), which is solid at room temperature, is technically available generally in the form of pellets and generally contains high levels of fine dust, possible with great safety precautions. Second, the process of dissolving the maleic anhydride (m3) pellets in the other monomers is accompanied by a great loss of time. The use of liquid maleic anhydride (m 3) provides an advantageous solution to these problems: on the one hand, it is no longer formed of fine dust during mixing, liquid maleic anhydride is commercially available; on the other hand, the liquid maleic anhydride is immediately dissolved in the monomer (ml) or in the monomer mixture (ml), (m2) and optionally (m4). The resulting solutions are generally storage stable in the mixing ratios indicated, and even for several months in the case of mixtures (ml) / (m3). During storage, there is no separation of maleic anhydride in the crystalline state. The use of monomer mixtures (ml) / (m 3) as a basic solution with a relatively high concentration of maleic anhydride (m 3) makes the process according to the invention predestined for the preparation of CP copolymers containing strong

  proportions of maleic anhydride (m3).

  The CP copolymers prepared by the process according to the invention in the absence of dyes or pigments have a high transparency and show practically no color pitting, problems that are encountered both in the case of preparation of such

  CP copolymers with maleic anhydride (m3) solid.

  The following examples are intended to illustrate the invention. Examples Preparation of the monomer mixture M1 400 g of maleic anhydride which is at a temperature of 60 ° C and is therefore in the liquid physical state are introduced into 3000 g of methyl methacrylate. The result is a clear and stable solution that keeps storage stable for several weeks. At best, this operation can be performed with agitation. 600 g of styrene, 1.68 g of dilauroyl peroxide and 0.4 g of tert-butyl perisononanoate are then added as polymerization initiators, 6.7 g of 2-mercaptoethanol as a weight regulator.

  molecular weight, as well as 4 g of 2- (2-hydroxy-5-

  methylphenyl) -benzotriazole as a UV absorber and 4 g of palmitic acid as an auxiliary demolding product. EXAMPLE 2 Preparation of TP1 terpolymer from the monomer mixture M1 prepared in Example 1 The M1 monomer mixture prepared in Example 1 was charged to a polymerization chamber and degassed

  for 10 minutes. After that, it is polymerized in the bath-

  married for 6 hours at 60 ° C, then bath temperature

  is lowered to 50 ° C and the polymerisation is

  continued for another 20 hours at 50 ° C.

  After about 25 hours, the polymerization mixture

  reached, with 144 ° C, its maximum temperature.

  After the polymerization chamber has been removed, the CP1 copolymer thus prepared is kept at a constant temperature of 120 ° C. for a further 12 hours in the air oven. The resulting CP1 polymer is colorless and transparent. It has a degree of yellowing according to DIN 5033/5036 of 2.3 and a transmission of light according to DIN 5033/5036 of 90.9%. The Vicat softening temperature of TP1 according to DIN 53460 is 121 ° C., the reduced viscosity according to DIN 51 562 is 59 ml · g -1, which corresponds to an average molecular weight X. about 10,000 daltons (compared with polymethacrylate

methyl>.

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Claims (9)

  1. A process for the preparation of CP copolymers by bulk polymerization of monomer mixtures x consisting of the following monomeric units:   <ml) 50 to 90% by weight of alkyl methacrylate   1 to 6 carbon atoms in the ester residue,   (m2) 5 to 25% by weight of at least one vinylaromatic compound tick,   (m3) 1 to 25% by weight of maleic anhydride and optionally   (m4) 0 to 5% by weight of alkyl acrylate containing 1 to 6 carbon atoms in the ester residue, the sum of (ml), (m2), (m3) and optionally (m4) being equal to 100% by weight, in the presence of PI polymerization initiators and XR molecular weight regulators, characterized in that before the polymerization, maleic anhydride (m 3) is added and mixed,   the liquid physical state, to the other monomers.   2. A process for the preparation of copolymers CP according to claim 1, characterized in that, in a first step, the maleic anhydride is premixed with the alkyl methacrylate (ml) in weight ratios (ml) / (m3) between 75/1 and 75/25 parts by weight and in a second stage the resulting mixture is added and mixed, before the polymerization, with the remaining monomers (m 2) and possibly (m4).   3.- Process for preparing CF copolymers according to   claims 1 or 2, characterized in that   maleic anhydride (m3) is added and mixed with   temperature of 55 to 80 ° C under an inert gas atmosphere.   4.- Process for preparing CP copolymers according to   any of claims 1 to 3, characterized   in that the PI polymerization initiators and the molecular weight regulators MR are added only after the preparation of the monomer mixture composed of the monomer units (ml), (m2), (m3) and optionally (m4). 5.- Process for preparing CP copolymers according to   any of claims 2 to 4, characterized   in that the monomer mixture (ml) / (m3) is stored temporarily before being added and mixed with   monomers (m2) and optionally (m4).   6.- Process for preparing CP copolymers according to   any of claims 1 to 5, characterized   in that the monomer component (ml) is methacrylate of methyl.   7.- Process for preparing CP copolymers according to   any one of claims 1 to 6, characterized   in that the monomer component (m2) is styrene and / or c-methylstyrene.   8. A process for the preparation of copolymers CP according to claim 6 or 7, characterized in that the monomer mixture contains 60 to 85% by weight of methacrylate   of methyl as a monomer component (ml).   9. Process for preparing CP copolymers according to   any of claims 1 to 8, characterized   in that the monomer (m4) is present in the monomer mixture M in proportions of 0.5 to 5% by weight.