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 appropriate locations were synthesized and added to vinylic monomer polymerization media, i.e., cumyl 4,6‐heptadienyl peroxide (CHP), ethyl 5‐cumylperoxy‐5‐methoxy‐2‐methylenehexanoate (ECMMH), 6‐cumylperoxy‐6‐methoxy‐3‐methylene‐2‐oxoheptane (CMMOH), N‐t ‐butyl‐ N ‐(2,2‐diethoxyethyl)acrylamide ( t BEEA), N‐t ‐butyl‐ N ‐(2,2‐diethoxyethyl)methacrylamide ( t BEEMA). Chemistry aspects of synthesis and stability of the compounds are discussed. The thermolysis activation energies of the peroxidic compounds were estimated from DSC measurements to adapt the reaction conditions to the stability of these compounds. These compounds were tested as potential new chain transfer agents, involving a radical addition on activate unsaturation and a subsequent substitution on OO or HC bonds. In the first case, an oxyl radical was expelled and, in the second one, the generated carbon‐centered radical was expected to evolve by a fast β‐scission of the adjacent CO bond to yield an alkyl radical. In both cases, these radicals would re‐initiate efficiently the polymerization cycle. It was found that, in contrast to previously studied compounds allowing efficient 1,3‐intramolecular homolytic substitutions (1,3‐S H i), the transfer properties of these “1,5‐substituted” compounds in the free radical polymerization of methyl methacrylate, styrene or butyl acrylate are poor in most cases. This behavior is discussed in terms of competition between intermolecular cross‐addition reaction (copolymerization) and 1,5‐intramolecular homolytic substitution (1,5‐S H i).