CHAIN TRANSFER BY ADDITION-FRAGMENTATION MECHANISM - 8 - STUDY OF TRANSFER AGENTS DESIGNED TO ALLOW 1,5-INTRAMOLECULAR HOMOLYTIC SUBSTITUTIONS

Some substituted olefins and dienes bearing weak bonds located in appr opriate locations were synthesized and added to vinylic monomer polyme rization media, i.e., cumyl 4,6-heptadienyl peroxide (CHP), ethyl 5-cu mylperoxy-5-methoxy-2-methylenehexanoate (ECMMH), 6-cumylperoxy-6-meth oxy-3-methylene-2-oxoheptane (CMMOH), N-t-butyl-N-(2,2-diethoxyethyl) acrylamide (tBEEA), N-t-butyl-N-(2,2-diethoxyethyl)methacrylamide (tBE EMA). Chemistry aspects of synthesis and stability of the compounds ar e discussed. The thermolysis activation energies of the peroxidic comp ounds were estimated from DSC measurements to adapt the reaction condi tions to the stability of these compounds. These compounds were tested as potential new chain transfer agents, involving a radical addition on activated unsaturation and a subsequent substitution on O-O or H-C bonds. In the first case, an oxyl radical was expelled and, in the sec ond one, the generated carbon-centered radical was expected to evolve by a fast p-scission of the adjacent C-O bond to yield an alkyl radica l. In both cases, these radicals would re-initiate efficiently the pol ymerization cycle. It was found that, in contrast to previously studie d compounds allowing efficient 1,3-intramolecular homolytic substituti ons (1,3-S(H)i), the transfer properties of these ''1,5-substituted'' compounds in the free radical polymerization of methyl methacrylate, s tyrene or butyl acrylate are poor in most cases. This behavior is disc ussed in terms of competition between intermolecular cross-addition re action (copolymerization) and 1,5-intramolecular homolytic substitutio n (1,5-S(H)i).