A chemical approach to the problem of slow initiation in living cationic polymerizations

The effect of slow initiation on initiation efficiency and MWD has been investigated, with regard to the living carbocationic polymerization of isobutylene. The initiating system trans−2,5-diacetoxy-2,5-dimethyl−3–hexene(DiOAcDiMeH₆)BCl₃ has been investigated at −35°C in CH₃Cl. Based on considerations valid also for anionic polymerizations, the following methods have been applied to increase the initiation efficiency: 1. Increasing M_o]/I_o] (batch, AMI) or ΔM].j/I_o] (IMA). The applicability of this method is limited by the solubility of the polymer. 2. Increasing k_i/k_p, by (i) increasing k_i, e.g., by introducing an electron withdrawing substituent into the initiator, (ii) decreasing k_p, e.g., by the addition of a strong electron donor (DMSO) to the system, (iii) using Cl-CH₂-CH₂-Cl.