Real-time mid-IR monitoring of the initiation and propagation in epoxi-initiated living isobutylene polymerizations

The initiation and propagation of isobutylene (IB) polymerization initiated by 1,2-cpoxi-2,4,4-trimethylpentane (TMPO-1)/TiCl4 was monitored by a new fiber-optic transmission mid-IR probe. The real-time IR data provided insig ht into the initiation mechanism. Polyether Formation, isomerization of the TMPO-1 into 2,4,4-trimethylpentanal, and its complexation by TiCl4 were ob served, which occurred simultaneously with initiation of IB polymerization. The proposed initiating mechanism involves the formation of tertiary carbo cations, which has been claimed to occur in the cationic polymerization of epoxides by the S(N)1 mechanism. On the basis of our results, the competiti ve occurrence of both SN1 and S(N)2 pathways is proposed. Interestingly, ke tone/TiCl4 systems were found to initiate IB polymerization, albeit with ve ry low efficiency. IR monitoring of these systems gave additional insight i nto the initiating mechanism. IB polymerization was monitored by following the disappearance of the second overtone of the C-H wag in the =CH2 group i n IB at 1780 cm(-1) and the C=C stretch at 1655 cm(-1). The linearity of fi rst-order monomer consumption plots and the production of nearly uniform po lyisobulylenes (PIBs) (M-w/M-n = 1.06-1.13) indicated living conditions.