N.m.r. characterization of functional groups: 5—on the nature of olefinic end groups in polyisobutylenes

Proton n.m.r. signals for two types of olefinic end groups, ‐CH 2 C(CH 3 )CH 2 (δ4.68 and δ4.87) and ‐CHC(CH 3 ) 2 (δ5.21), have been observed in high molecular weight polyisobutylenes. Comparable amounts of both these end groups exist in commercial and laboratory prepared samples of polyisobutylenes contrary to previous reports that the former group is by far predominant. That different catalysts produce different relative concentrations of these end groups is demonstrated. Evidence for the presence of a third type of unsaturation from the ‐CH 2 C(CH 2 )CH 2 ‐ structure is discussed.