Initiation of vinyl polymerization by tetrakis(triphenyl phosphine) platinum (0)

Abstract

Tetrakis (triphenyl phosphine) platinum (0), in association with a suitable organic halogen compound, is an active initiator of free-radical polymerization which does not give rise to inhibition at high halide concentrations. We report here a study of the polymerization of methyl methacrylate initiated by Pt(PPh₃)₄+ CCl₄. Although showing kinetic features which are generally similar to those of other systems incorporating zero-valent metal derivatives, this initiator is unusual in several respects. The activation energy for initiation is low (11.2 kcal mole^–1) so that initiation may be usefully effected over a wide range of temperatures, extending from 80°C to below room temperature. The frequency factor for initiation is abnormally low; an explanation based on steric obstructions encountered in the formation of a transition state involving monomer or solvent, is advanced. Further, initiation is relatively inefficient, a comparatively small portion of the platinum derivative reacting by a radical-producing route.