TEMPLATE POLYMERIZATION OF N-VINYLIMIDAZOLE ALONG POLY(METHACRYLIC ACID) IN WATER .3. MOLECULAR-WEIGHTS OF THE FORMED POLYMERS

The molecular weights of polymers formed in the template polymerization of N-vinylimidazole (VIm) along poly(methacrylic acid) (PMAA) in water at 50-degrees-C using 2,2'-azobis(2-amidinopropane)-2HCl (AAP) as initiator were determined for variable [PMAA] to [VIm]0 ratios, [VIm]0, [AAP]0, and template molecular weight. Molecular weights were up to 70 times higher than those of polymers produced in the absence of the PMAA template, which is probably mainly due to retardation of termination of radicals propagating alongside the template. Longer templates appeared to promote retardation of termination. Frequent radical hopping to other template chains on reaching template ends led to polymers with molecular weights up to 9 times higher than the template molecular weight. From a comparison of molecular weights with corresponding rate enhancements as a function of [PMAA]/[VIm]0, it is suggested that the M(v) of the daughter polymer was further increased by combination termination of two template-associated radicals (template termination), while cross-termination with short radicals and possibly radical occlusion becomes more important at higher [PMAA]/[VIm]0. Primary termination may occur because of an enhanced local concentration of the positively charged initiator close to the template chains.