Process for the production of heat resistant thermoplastic copolymer

#This invention relates to a process for the production of a heat resistant thermoplastic copolymer. More particularly, the invention relates to a process for the production of a thermoplastic copolymer having excellent heat distortion resistance which is characterized by converting carboxyl groups in the molecule of the polymer into anhydride groups by heating-treating the raw copolymer containing carboxyl groups in the presence of a ring-closing promoter.

#Thermoplastic copolymers, particularly polymethyl methacrylate, polystyrene, and methyl methacrylate-styrene copolymers, have desirable characteristics such as excellent transparency, mechanical properties and processability and hence have widely been used in various fields such as automobile parts, electrical parts, industrial parts, miscellaneous goods, and the like.

#However, with the expansion of the utilities of these materials, it is required to obtain resin materials having more improved heat distortion resistance and more improved transparency and mechanical properties. Extensive investigation has been conducted for obtaining materials having such required properties. For instance, it is known that a polymer having excellent heat distortion resistance can be produced by copolymerizing methacrylic acid and methyl methacrylate and/or styrene. Generally speaking, however, a methacrylic copolymer resin has high water absorption properties and hence shows low heat resistance due to the water absorption, and further, when the resin is processed to obtain formed products, the products have unsatisfactory splash (stripe, etc.) on the back surface thereof due to generation of volatile materials induced by dehydration during the forming and processing steps.

#A 5 liter autoclave provided with a stirrer is charged with water (2.2 liter) and hydroxyethyl cellulose (2.4 g), and thereto are added methacrylic acid (160 g), methyl methacrylate (1440 g), laurylmercaptane (6.4 g) and lauroyl peroxide (5.6 g), and the mixture is polymerized by heating at 80.degree. C. with agitation for one hour and 40 minutes. After raising the temperature to 98.degree. C., the mixture is further agitated for one hour, by which the polymerization reaction is completed. The polymerization mixture is cooled, and the polymer is separated by centrifugation, washed with water and dried at 80.degree. C. The polymer beads thus obtained have a content of methyl methacrylate of 90% by weight and methacrylic acid of 10% by weight. The dried beads (100 parts by weight) are mixed with sodium hydroxide (0.03 part by weight) with a Henschel mixer and then pelletized with a 40 mm deaeration extruder (VS 40-28 type, L/D=28, manufactured by Tanabe Plastic Kikai K.K.) at a screw rotation speed of 50 rpm at a resin temperature of 280.degree. C.

#As to the pellets, there were measured the ring-closing ratio and melt flow index (MI). Besides, the pellets were formed by injection molding at 260.degree. C., and the surface of the formed product was observed, and further, the heat distortion temperature (HDT) was measured. The results are shown in Table 1.

#In the same manner as described in Example 1 except that the used amounts of the materials are varied as shown in Table 1, there are produced various products.