Radical copolymerization of lithium p-styrenesulfonate followed by homopolymerization of a less-reactive comonomer with spontaneous delay

Radical copolymerization of lithium p-styrenesulfonate (LiSS) was investigated in aqueous media under various comonomer, initiator, and solvent conditions. The copolymerization of LiSS with acrylamide (AAm) provided random copolymers with LiSS-rich composition at an earlier stage of the reaction, then the homopolymerization of AAm started with spontaneous delay after the almost consumption of LiSS at a conversion over 95%. Such unique polymerization behavior was observed for the copolymerization of highly reactive sulfonate monomers such as LiSS and sodium p-styrenesulfonate (NaSS) combined with less-reactive comonomers such as AAm, N-vinylacetamide, and potassium 3-(acryloyloxy)propanesulfonate. The reaction mechanism and kinetic features for the two-step polymerization consisting of random copolymerization followed by the spontaneously delayed homopolymerization are described in detail.