THERMAL STYRENE-CO-ACRYLONITRILE DISCOLORATION PROBLEM - THE ROLE OF SEQUENCE DISTRIBUTION AND OLIGOMERS

Styrene-co-acrylonitrile resins (SAN) are important commercial thermoplastic materials. However, SAN discolors during molding, the extent of which is dependent upon the AN content of the polymer. GPC-UV/vis analysis of discolored SAN indicates that both monomer sequence distribution in the backbone and small molecules are involved in the formation of chromophores and that the main backbone chromophore resides on the chain end. The product of reactivity ratios (calculated from monomer sequence distribution data) of high-temperature (140-160-degrees-C), CSTR-produced SAN copolymers is higher than typically reported for low-conversion batch copolymerization. Possible mechanisms are proposed for (1) a high reactivity ratio product, (2) SAN polymer backbone discoloration, and (3) the formation of small colored molecules.