In situ quenching and post-polymerization modification of telechelic polyisobutylene
Polyisobutylene (PIB) is a saturated hydrocarbon elastomer that can only be produced by cationic polymerization. The water-initiated, chain transfer controlled synthesis conducted on an industrial scale produces monofunctional PIB with mixed olefin end groups. Living cationic techniques produce mono- and di-functional telechelic PIB. In situ quenching is the process of adding functional molecules to the polymerization reactor after all monomer is consumed. These quencher species bond to the chain ends, installing their latent functionality onto the polymer chain. To date, all quenchers utilized have been soft π-nucleophiles. In the first project, free thiols, both aromatic and aliphatic, are shown to be effective quenchers of living PIB. These soft nucleophiles lack π electrons, but are sufficiently nucleophilic to directly attack a carbocation in an S N 1 reaction and form sulfide bonds with the polymer chain. By utilizing functional thiols, functional PIBs can be produced directly from the polymerization reactor, with no post-polymerization modification. The second project utilized an established alkoxybenzene quencher, 3-bromopropoxy benzene, to produce bromine-terminated PIB. This material was then reacted with several functionalized carboxylates to displace the terminal bromine unit and produce PIBs with acrylate, methacrylate, and hydroxyl end groups. The fourth chapter used two approaches to generate hydroxyl-terminated PIB. The first used an in situ quenching/deblocking sequence with living PIB to produce phenol-terminated PIB. The second used exo -olefin PIB in a radical thiol-ene reaction with 2-mercaptoethanol to produce aliphatic hydroxyl-terminated PIB. These functional PIBs are reacted with acid halides to produce telechelic PIB-based macromers and macroinitiators for radical copolymerizations.