The effect of cross-linking density on the termination mechanism in network radical polymerization

Abstract

The diffusion control of termination in radical polymerization involving multivinyl monomers results in an alternative mechanism of bimolecular termination, namely in the reaction diffusion. By studying photo-initiated polymerization and copolymerization of mono- and dimethacrylates, the influence of polymer cross-linking density and monomer structure on reaction diffusion parameter R was determined. A reduction of cross-linking density results in the shift of reaction diffusion controlled termination towards high conversion. In loosely cross-linked systems, the reaction diffusion may not control the termination. It is proposed that the apparent increase in R with conversion beyond its steady value that begins at the conversion range of maximum polymerization rate is associated with a change of termination mechanism. Then the rate equations for bimolecular reaction fail to describe the process.