Process for preparing copolymers comprising .alpha.-alkyl styrene and unsaturated nitrile

#The present invention relates to an improved process for preparing copolymers having an excellent thermal resistance with marked decrease in the amount of unreacted monomers.

#At the present time, heat-resistant ABS resins obtained by admixing .alpha.-methylstyrene-acrylonitrile copolymers and styrene-acrylonitrile-butadiene graft polymers are widely employed. However, the heat-resistance of such ABS resins is not satisfactory for some purposes, and the appearance of thermoplastic resins having a higher heat-resistance is desired.

#The heat-resistance temperature of heat-resistant ABS resins is mainly dependent on the heat-resistance temperature of the .alpha.-methylstyrene-acrylonitrile copolymers constituting the matrix, and the heat-resistance temperature of such copolymers is influenced by their .alpha.-methylstyrene content. Thus, with a larger content of .alpha.-methylstyrene, a higher heat-resistance is obtained. However, .alpha.-methylstyrene is less reactive in the radical polymerization, and it is difficult to polymerize .alpha.-methylstyrene alone, i.e. without copolymerization with acrylonitrile or other monomers. Therefore, in the preparation of .alpha.-methylstyrene-unsaturated nitrile copolymers containing a higher content of .alpha.-methylstyrene, the amount of .alpha.-methylstyrene to be used is naturally restricted for decreasing the concentration of unreacted monomers to less than 1% by weight (to the entire amount of the monomers charged) at completion of the polymerization.

#Into a reaction vessel wherein the atmosphere was replaced by nitrogen, deionized water (140 parts), sodium laurylsulfate (3 parts), potassium persulfate (0.7 part) and n-dodecylmercaptan (0.1 part) were charged, and the temperature was elevated up to 70.degree. C. A mixture of .alpha.-methylstyrene (75 parts) and acrylonitrile (5 parts) was added thereto continuously in 6 hours. With regulation of the concentration of the unreacted acrylonitrile, .alpha.-methylstyrene (3 parts) and acrylonitrile (17 parts) were added thereto in 2 hours. The concentration of the unreacted acrylonitrile in the reaction system at completion of the addition of the monomers was 33%. Then, the polymerization was further continued for 2 hours. The concentrations of the unreacted .alpha.-methylstyrene and of the unreacted acrylonitrile in the reaction mixture at completion of the polymerization were respectively 0.68% and 0.21% to the entire amount of the used monomers.

#Into a reaction vessel wherein the atmosphere was replaced by nitrogen, deionized water (140 parts), sodium laurylsulfate (3 parts), potassium persulfate (0.7 part) and n-dodecylmercaptan (0.1 part) were charged, and 20% of a mixture of .alpha.-methylstyrene (69 parts) and acrylonitrile (20 parts) was added thereto. The temperature was elevated up to 70.degree. C. After the initiation of the polymerization, 80% of the said monomer mixture was continuously added to the reaction system in 5 hours. With regulation of the concentration of the unreacted acrylonitrile, .alpha.-methylstyrene (2 parts) and acrylonitrile (9 parts) were added thereto in 2 hours. The concentration of the unreacted acrylonitrile in the reaction system at completion of the addition of the monomers was 51%. Then, the polymerization was further continued for 2 hours. The concentrations of the unreacted .alpha.-methylstyrene and of the unreacted acrylonitrile in the reaction mixture at completion of the polymerization were respectively 0.38% and 0.20% to the entire amount of the used monomers.

#Into a reaction vessel wherein the atmosphere was replaced by nitrogen, deionized water (140 parts), sodium laurylsulfate (3 parts), potassium persulfate (0.7 part) and n-dodecylmercaptan (0.1 part) were charged, and .alpha.-methylstyrene (74 parts) was added thereto. The temperature was elevated up to 70.degree. C. Acrylonitrile (26 parts) was added thereto continuously in 8 hours. After 4 hours from the initiation of the addition of acrylonitrile, the concentration of the unreacted acrylonitrile in the reaction system was measured. The concentration of the unreacted acrylonitrile in the reaction system at completion of the addition of the monomers was 45%. Then, the polymerization was further continued for 2 hours. The concentrations of the unreacted .alpha.-methylstyrene and of the unreacted acrylonitrile in the reaction mixture at completion of the polymerization were respectively 0.60% and 0.30% to the entire amount of the used monomers.