The use of activated benzyl vinyl ethers to control molecular weight in free radical polymerizations

The vinyl ethers, α‐benzyloxyacrylonitrile ( 4 ), methyl α‐benzyloxyacrylate ( 5 ), and α‐benzyloxy‐acrylamide ( 6 ), act as sulfur‐free chain transfer agents in the polymerization of methyl methacrylate (chain transfer constant C x = 0,081–0.47), styrene ( C x = 0,036–0,14), methyl acrylate ( C x = 0,3–1,1), and vinyl acetate ( C x = 12–20) initiated by AIBN at 60°C. With methyl methacrylate and styrene, the conversions of the polymerizations are relatively unaffected by the vinyl ethers. With methyl acrylate and vinyl acetate, however, some retardation occurs. The activity of the compounds is compared with that of α‐benzyloxystyrene ( 1 ), which undergoes chain transfer by a novel free radical addition‐fragmentation pathway.