Synthesis of Hyperbranched Polyisobutylenes by Inimer-Type Living Polymerization. 1. Investigation of the Effect of Reaction Conditions

Abstract

Hyperbranched polyisobutylenes (PIBs) have been synthesized by carbocationic copolymerization of an inimer (initiator-monomer, IM) and isobutylene (IB). The IM used was 4-(2-methoxyisopropyl)styrene (p-methoxycumylstyrene, pMeOCumSt), in conjunction with TiCl4 as a co-initiator in methylcyclohexane (MeCHx)/methyl chloride (MeCl) 60/40 v/v solvent mixture at −80 °C, in the presence of 2,6-di-tert-butylpyridine (DtBP) as a proton trap. The effect of reaction conditions on the molecular weights (MW), molecular weight distributions (MWD), and branching frequencies (BR) was investigated. Hyperbranched PIBs with MWs up to Mn ≈ 8 × 105 g mol-1 and MWD as low as 1.2 were obtained within 15−60 min reaction time, where under the same conditions the 2-chloro-2,4,4-trimethylpentane (TMPCl) monofunctional initiator would have yielded MWs in the range of Mn ≈ 104 g/mol. BRs were determined by selective destruction of the branching points (links) and taking the ratio of the MWs before and after link destruction. The experimental BR values, ranging from 3 to 57, agreed reasonably well with values calculated using the formula BR = (Mn/Mn(theo)) − 1, where Mn is the total MW of the hyperbranched PIB, and Mn(theo) would be the MW if the IM would act as initiator only. The process was scaled up to 400 g of PIB/batch, sufficient for meaningful physical characterization.