Tailored macromolecules by living carbocationic techniques

Abstract

This presentation concerns our latest results for the controlled synthesis of various homopolymers, blocks, random copolymers, networks, by living carbocationic polymerization (LC⊕ Pzn). We start with an analysis of the Winstein ionicity spectrum, a roadsign toward LC⊕ Pzn systems. Living isobutylene (IB) homopolymerization can be effected by the addition of common anion salts to conventional polymerization charges, e.g., by adding nBu4NCl to a 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl4/IB system. Various AB diblocks have been prepared by sequential monomer addition. The first clean svnthesis of an AB poly(olefin-b-alkyl vinyl ether) diblock, ie., poly(isobutylene-b-methyl vinyl ether), by sequential monomer addition was accomplished. These novel amphiphilic diblocks promise to be excellent nonionic detergents. The field of linear A-B-A triblocks and three-arm star blocks where A = glassy and B = rubbery (polyisobutylene) segment, is vigorously expanding. Several new thermoplastic elastomers (TPEs) have been prepared, characterized and tested, e.g., poly-(indene-b-isobutylene-b-indene). The synthesis of random copolymers, e.g., isobutylene/2,4,4-dimethyl-1,3-pentadiene, by living reactivity leveling has been demonstrated. Transformation of the polyisobutylene cations PIB⊕ and ⊕PIB⊕ yielded the corresponding anions PIB⊖ and ⊖PIB⊖, which upon block polymerization of butadiene (Bd) and methyl methacrylate (MMA), respectively, gave rise to the new diblock PIB-PBd and triblock PMMA-PIB-PMMA. In the latter, the largely syndiotactic sPMMA endblocks were stereocomplexed with isotactic iPMMA and thus the upper use-temperature of these novel TPEs was enhanced. Novel amphiphilic networks comprising hydrophilic polymethacrylates (e.g., dimethylaminoethyl methacrylate (DMAEMA) or hydroxyethyl methacrylate (HEMA)) crosslinked by methacrylate-telechelic PIBs were prepared and their potential usefulness for biomedical applications has been studied.