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

Hyperbranched polyisobutylenes (PIBs) have been synthesized by carbocationic copolymerization of an inimer ( ini tiator-mono mer, IM ) and isobutylene (IB). The IM used was 4-(2-methoxyisopropyl)styrene ( p -methoxycumylstyrene, pMeOCumSt), in conjunction with TiCl 4 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 (D t BP) 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 M n ≈ 8 × 10 5 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 M n ≈ 10 4 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 = ( M n / M n(theo) ) − 1, where M n is the total MW of the hyperbranched PIB, and M n(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.