Synthesis of hyperbranched polyisobutylenes by inimer-type living polymerization. 1. Investigation of the effect of reaction conditions

Hyperbranched polyisobutylenes (PIBs) have been synthesized by carbocationi c copolymerization of an inimer (initiator-monomer, IM) and isobutylene (IB ). The IM used was 4-(2-methoxyisopropyl)styrene (p-methoxycumylstyrene, pM eOCumSt), in conjunction with TiCl4 as a co-initiator in methylcyclohexane (MeCHx)/methyl chloride (MeCl) 60/40 v/v solvent mixture at -80 degreesC, i n the presence of 2,6-di-tert-butylpyridine (DtBP) as a proton trap. The ef fect of reaction conditions on the molecular weights (MW), molecular weight distributions (MWD), and branching frequencies (BR) was investigated. Hype rbranched PIBs with MWs up to M-n approximate to 8 x 10(5) g mol(-1) and MW D as low as 1.2 were obtained within 15-60 min reaction time, where under t he same conditions the 2-chloro-2,4,4-trimethylpentane (TMPCl) monofunction al initiator would have yielded MWs in the range of M-n approximate to 10(4 ) g/mol. BRs were determined by selective destruction of the branching poin ts (links) and taking the ratio of the MWs before and after link destructio n. The experimental BR values, ranging from 3 to 57, agreed reasonably well with values calculated using the formula BR = (M-n/Mn-(theo)) - 1, where M -n is the total MW of the hyperbranched PIE, 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/match, sufficient for meaningful physical characterization.