Living Carbocationic Polymerization. XXIII. Analysis of Slow Initiation in Living Isobutylene Polymerization

The aim of this research was to develop a quantitative treatment of the consequences of relatively slow initiation on M _n and N (the number of molecules formed, W_p/M _n , where W_p =weight of polymer formed) in living carbocationic polymerizations, particularly for the case of the incremental monomer addition (IMA) technique. This has been achieved by analysis of the effect of initiator efficiency (I_eff (%) = 100N/[I ₀], where [I ₀] = initiator input) on M _n versus W_p , and N versus W_p plots. Three types of systems have been discerned: 1) I_eff equal to 100%; 2) I_eff constant but less than 100%; and 3) I_eff less than 100% but increasing with increasing number of monomer increments j by the IMA technique. Thus conditions can be found under which slowly initiating systems yield close to “ideal” product, i.e., one with M _n = [M₀ ]/[I₀ ] and narrow molecular weight distribution (M _w /M _n ≈ 1.1). The corresponding equations and plots can be used to diagnose the mechanism. Subsequently, this quantitative analysis was used to describe a novel living system, trans‐2,5‐diacetoxy‐2,5‐dimethyl‐3‐hexene (DiOAcDMH₆)/BCI₃/isobutylene/CH₃CI. This system produces linear t‐chlorine‐telechelic polyisobutylenes under homogeneous conditions. Surprisingly, cationation seems to be rate determining. This conclusion is illustrated by chemical equations.