ON THE THERMAL COPOLYMERIZATION OF STYRENE WITH ACRYLONITRILE

The spontaneous thermal copolymerization of styrene (St) with acryloni trile (AN) was studied at 100 and 125 degrees C. Control experiments s howed that AN alone does not spontaneously homopolymerize at these tem peratures. Dilution with propionitrile, an inert model for AN, showed that, at a 1/4 St/AN feed ratio, the initiating radicals are generated by reaction of St with AN. For a 1/1 feed ratio at 100 degrees C the copolymerizations proceeded faster than the homopolymerization of St, while a monomer feed of 1/4 St/AN led to the fastest rates. The inhere nt viscosity was constant with time during the run. Maximum rates mere observed for a 40/60 St/AN monomer feed ratio, both in bulk and in pr opionitrile. The yield of small molecules was very low, reaching a max imum of similar to 3%. The small molecules consisted mostly of StAN(2) trimers, with minor contributions of the St(2)AN trimer and StAN-cycl obutane adduct. The latter two were not observed in the 1/6 St/AN run. These results lead us to conclude that a Mayo-type mechanism is in ef fect for this initiation. The results are compared to the previously s tudied photochemical polymerization of St and AN.