Living carbocationic polymerization. IV. Living polymerization of isobutylene

Abstract

Truly living polymerization of isobutylene (IB) has been achieved for the first time by the use of new initiating systems comprising organic acetate‐BCl 3 complexes under conventional laboratory conditions in various solvents from −10 to −50°C. The overall rates of polymerization are very high, which necessitated the development of the incremental monomer addition (IMA) technique to demonstrate living systems. The living nature of the polymerizations was demonstrated by linear Mn versus grams polyisobutylene (PIB) formed plots starting at the origin and horizontal number of polymer molecules formed versus amount of polymer formed plots. DPn obeys [IB]/[CH 3 COOR t · BCl 3]. Molecular weight distributions (MWD) are very narrow in homogeneous systems (Mw/Mn = 1.2–1.3) whereas somewhat broader values are obtained when the polymer precipitates out of solution (Mw/Mn = 1.4–3.0). The MWDs tend to narrow with increasing molecular weights, i.e., with the accumulation of precipitated polymer in the reactor. Traces of moisture do not affect the outcome of living polymerizations. In the presence of monomer both first and second order chain transfer to monomer are avoided even at −10°C. The diagnosis of first and second order chain transfer has been accomplished, and the first order process seems to dominate. Forced termination can be effected either by thermally decomposing the propagating complexes or by nucleophiles. In either case the end groups will be tertiary chlorides. The living polymerization of isobutylene initiated by ester. BCl 3 complexes most likely proceeds by a two‐component group transfer polymerization.