Addition-fragmentation behavior of a capto-dative group-substituted acrylic ester in free-radical polymerization and reactivity of the derived macromonomers

Ethyl-2-(2-cyano-2-ethylthio)-ethyl-propenoate (ECEP) was synthesized and e xamined as free-radical addition-fragmentation chain transfer agent (AFCTA) in the bulk polymerization of methyl methacrylate (MMA) and styrene at var ious temperatures. A better chain transfer constant (C-tr) was observed for styrene than for MMA, projecting the potentiality of the compound as a bet ter end-functionalizing agent for the former. In both cases, copolymerizati on of ECEP with the monomer predominated over fragmentation, the relative p roportions of which were dependent on the monomer. The ECEP-terminated radi cal fragmented to an extent of 26% in the presence of MMA, whereas it was o nly 9.5% in the case of styrene. The relative extent of fragmentation and c opolymerization was in conformation to the calculated reactivity ratios and chain transfer constants. Addition-fragmentation chain transfer resulted i n the formation of methacrylic-functional macromonomers. The copolymerizabi lity of the resultant macromonomer was found to depend on the nature of the backbone and on the comonomer. On copolymerizing with MMA, the terminal mo nomer moiety on polystyrene (PS)-based macromonomers preferred to undergo f ragmentation, whereas that of the polymethyl methacrylate (PMMA)-based one copolymerized readily with styrene because of thermodynamic and kinetic fac tors. (C) 1999 John Wiley & Sons, Inc.