Macromolecules, Vol.28, No.2, 622-626, 1995
On the Thermal Copolymerization of Styrene with Acrylonitrile
The spontaneous thermal copolymerization of styrene (St) with acrylonitrile (AN) was studied at 100 and 125 degrees C. Control experiments showed that AN alone does not spontaneously homopolymerize at these temperatures. 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 inherent 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 propionitrile. The yield of small molecules was very low, reaching a maximum of similar to 3%. The small molecules consisted mostly of StAN(2) trimers, with minor contributions of the St(2)AN trimer and StAN-cyclobutane 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 effect for this initiation. The results are compared to the previously studied photochemical polymerization of St and AN.
Keywords:DIELS-ALDER CYCLOADDITION;ELECTROPHILIC OLEFINS;INITIATION;MECHANISM;POLYMERIZATION;COMPETITION;DIRADICALS;OLIGOMERS;SYSTEM