DE1745763B1 - Process for the production of polymethyl methacrylate - Google Patents

Description

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It is known that methyl methacrylate, optionally with 7 to 9 carbon atoms, consists of the former in can be used together with certain proportions of certain vinyl amounts up to 75 mole percent compounds, in aqueous dispersion in the presence of can.

of an aliphatic thiol in an amount of 0.01. Surprisingly, by using

up to 3 percent by weight, based on the methyl mercaptans of different molecular weight, the formation methacrylate, eliminated at a temperature of at least the extremely disruptive vitreous. 100 ° C and to polymerize under autogenous pressure This has the advantage that a (U.S. Patent 2,450,000). As suitable thiols, large part (up to 75 mole percent) of the expensive ones include alkyl mercaptans with 1 to higher mercaptans due to much cheaper ones 16 carbon atoms listed. io lower mercaptan can be replaced. Since besides-

In the production of polymethyl methacrylate, the regulating effect of the mercaptan decreases with the with the increase in the molar weight of the mercaptan in the plastic mass industry, it also becomes common processing machines can be processed, the total amount is significantly reduced, by polymerization of methyl methacrylate in water So have z. B. 0.2% primary butyl mercaptan (from

engined suspension must be a ⁰ to 90 C 15 molecular weight 90) turn the same control effect as 0.4% translated strong shock reaction accepted primary-octyl mercaptan of molecular weight at about 80 146. When, the temperature in a few minutes is therefore half of the octyl mercaptan, which drifts up to about 130 to 135 ° C, is replaced with a simultaneous equivalent amount of butyl mercaptan, thus increasing the pressure to several atmospheres. 0.1% butyl mercaptan + 0.2% octyl is required. This reaction surge is difficult to control and 20 mercaptan, i.e. a total of 0.3%> ^um often leads to fluctuations in production. This same molecular weight of the polymer as with undesired reaction shock can be mitigated to obtain 0.4% octyl mercaptan alone. Still gün- and the temperature be kept below 100 ⁰ C, stiger is the ratio, when three quarters of the primary when used as a controller mercaptans. Replaced octyl mercaptans. You then need products with a low molecular weight, 25 equal molecular weight of the polymer instead of 0.4%, which can easily be processed on conventional machines with octyl mercaptan only 0.1 + 0.15% butyl mercaptan. A total of only 0.25% is required to carry out this process. Suitable mercaptans which have fewer than 10 carbon atoms in lower mercaptans are those of C ₃

the fatty alcohol chain and the grouping — CH ₂ —SH to C ₅ , optionally also C ₈ , understood; which contain. Mercaptans that contain more than 10 carbon atoms in 30 above them than higher mercaptans on the fatty alcohol chain, as well as mercap- watch.

- tane with the grouping ■ · The polymerization to be used according to the invention

. The process differs from the usual one up to now

- C - SH, method for bead polymerization of methyl meth-

35 acrylate without the addition of mercaptan in that the

deliver products which, in the usual processing methods used up to now, take advantage of the strongly exothermic temperatures of, for example, 200 to 250 ° C yellow or brown reaction of the monomers and the temperature will be used. In this simple form, the process has driven up temperature to at least 130 ⁰ C, but are technical serious drawbacks. must, in order to polymers with low molecular weights

When using easily accessible lower 40 and processable "material to be achieved. On the other hand mercaptans, such as propyl and butyl mercaptan, according to the invention, it is obtained by using the pressure optically excellent polymers, the mercaptans given the opportunity to PoIyjedoch have the disadvantage at temperatures of merisate of low molecular weights also at Tempeetwa 200 ° C for self-decomposition with regression, temperatures below 100 ° C, e.g. between 80 and of monomers tend to be. This can produce bubbles of 45 100 ° C, causing an overlay of the lead formations in the workpieces, thereby avoiding these mercaptan effects and temperature effects become inferior. will. Through precise dosing of the mercaptans

By using high molar mercaptans (± 0.001%) it is possible according to the invention for the first time, such as octyl or nonyl mercaptan, that the molar weights of the polymer within the self-decomposition temperature may be 250 to 260 ° C, so ± 1000, e.g. within 89000 and 91,000, ie constantly increased to technically usable temperatures. The accuracy even surpasses that of the will; However, these mercaptans give rise to the formation of polymers with the precision of the determination of the molecular weight of the merization in aqueous suspension.

of non-melting vitreous bodies that result from US Pat. No. 2,450,000 is the

different light refraction the workpiece is known optically 55 addition of a mercaptan, but it contains make unequal and with larger quantities also opaque no indication of the use of mixtures can do. from mercaptans in general or even from the at

There has now been a method of making specific methods used in the present invention Could stimulate polymethyl methacrylate by polymerizing mercaptans. She doesn't say anything either Methacrylic acid methyl ester, optionally together 60 about the different effects of the lower and with alkyl esters of acrylic acid or methacrylic acid, higher mercaptans and addresses the problem in the case of aqueous suspension in the presence of mercap as in the suspension polymerization of methyltanes found in which it is possible to easily methacrylate prevents the formation of vitreous bodies workable, thermally stable and can be made of vitreous, not at all a. to produce free polymethyl methacrylate by 65 of the US Pat. No. 2,450,000 that one obtainable in the presence of a mercaptan mixture using only one mercaptan works, which consists of a primary mercaptan with polymers differ according to the er-3 up to 6 carbon atoms and a primary mercaptan according to the method of the invention

advantageous due to their easier processing, their better thermal stability and heat resistance. In addition, they are completely free of glass bodies and therefore optically flawless.

The process is not only suitable for the polymerization of pure methyl methacrylate, but also to mixtures of the same with other alkyl esters of acrylic acid or methacrylic acid, such as methyl acrylate, Butyl acrylate, butyl methacrylate can be used.

IO

example 1

80 g of primary butyl mercaptan, 170 g of primary ethylhexyl mercaptan and 800 g of benzoyl peroxide are dissolved in 100 kg of methyl methacrylate. This solution is suspended in 300 l of water in which 240 g of sodium polyacrylate are dissolved by vigorous stirring and heated to 80 ° C. with constant stirring. The now ensuing reaction is moderated by external cooling so that the internal temperature does not exceed 9O ⁰ C ao increases. After the main reaction has ended, the temperature is maintained at 95 ° C. for a further 90 minutes. After a total of 3 hours, the polymerization has ended with a conversion of 99 to 99.5 ° / q. The polymer present in fine beads is separated from the aqueous phase, washed salt-free and dried. Its molecular weight is 95,000, its softening point 156 ° C. (according to the ASTM D 569 method). The product can be processed into any desired workpieces by the methods customary in the plastic material industry, which are absolutely colorless and crystal clear and ^{do not change optically even at high processing temperatures (up to 250 °} C.) and also do not show any incipient self-decomposition. The workpieces are visually completely homogeneous.

Example 2

The procedure is as in Example 1, with the difference that 120 g of primary butyl mercaptan and 110 g primary ethylhexyl mercaptan can be used. The result corresponds to that of example 1, since the effect sum the mercaptans is the same.

Example 3

60 g of primary butyl mercaptan, 150 g of primary octyl mercaptan and 800 g of benzoyl peroxide are dissolved in a mixture of 95 kg of methyl methacrylate and 5 kg of butyl acrylate. This solution is dissolved in 500 1 of water in which 300 g of polyacrylic acid, sodium, suspended by brisk stirring and heated under constant agitation to 7O ⁰ C. The slow-onset reaction is moderated by external cooling so that the internal temperature does not exceed 98 ⁰ C. After the main reaction has ended, the mixture is ^{held at 98 °} C. for a further 2 hours. After a total of 3 ¹ I ₂ hours, the polymerization is completed with a conversion of about 98%. The polymer present in fine beads is separated from the aqueous phase, washed salt-free and dried. Its molecular weight is 101000, the softening point 146 ⁰ C (ASTM D 569). The polymer can be reduced to the usual processing machine at 200 to 21O ⁰ C to any workpieces processed, which are absolutely colorless and clear and at 200 ⁰ C for 24 hours are optically stable. The workpieces are visually completely homogeneous.

Claims (1)

Claim: Process for the production of polymethyl methacrylate by polymerizing methyl methacrylate, optionally together with other alkyl esters of acrylic acid or methacrylic acid, in aqueous suspension in the presence of mercaptans, characterized in that that one works in the presence of a mercaptan mixture, which from a primary Mercaptan with 3 to 6 carbon atoms and a primary mercaptan with 7 to 9 carbon atoms, the former can be used in an amount up to 75 mole percent.