New insights into the mechanism of 1,2-bis(trimethylsilyloxy)-tetraphenylethane-induced free radical polymerization: Application to the synthesis of block and graft copolymers

1,2-Bis(trimethylsilyloxy)tetraphenylethane (TPSE) was used to polymerize methyl methacrylate (MMA) and styrene (S) between 70 and 130°C. TPSE is actually found to act as an initiator in the case of MMA and as a terminating agent as well. Chain propagation is controlled by the reversible deactivation of growing polymeric radicals with diphenylmethyl (DPM) radicals that result from the homolytic decomposition of TPSE. In the case of styrene, the mechanism is more complex: chain growth appears to involve the degenerative transfer of TPSE hemifragments (DPM) from chain to chain; unfortunately, this process is not efficient enough to curb irreversible termination. The conditions that are most appropriate to prepare block and graft copolyrners using TPSE as initer are described. Copolymers constituted of poly(methyl methacrylate) (PMMA) grafts or blocks with relatively well-defined structures are obtained with this technique.