Transfer and Termination Reactions in “Living” Carbocationic Polymerizations

Abstract

Abstract The available data concerning the polymerization of three classes of monomers deemed to yield living polymers, vinyl ethers, styrenic monomers and isobutylene, are discussed from the point of view of transfer and termination reaction. In the case of vinylethers, linearity of [Mbar]n with a yield up to 30,000 has been obtained, but when higher [Mbar]n are planned, there is evidence for the occurrence of transfer reactions. In the case of isobutylene, indene, and p-Me-styrene, the linearity (up to [Mbar]n ∼ 105) of [Mbar]n with the amount of monomer polymerized which has been observed (but only at low temperature) is compatible with values of transfer constants to monomer measured in “conventional” systems. In these living systems, irreversible terminations are often not very important but may become significant toward the end of monomer consumption. The main termination process is reversible termination which may lead to narrow molecular weight distributions. The linearity of [Mbar]n with yield is not conclusive evidence for the absence of transfer and termination and for the presence of particular active centers. The control of the polymerizations achieved up to now can be accounted for by the mechanisms of conventional cationic polymerizations, transfer reactions included.