Thiol-terminated polyisobutylene: Synthesis, characterization, and derivatization

Abstract

Thiol-terminated polyisobutylene (α,ω-PIB-SH) was synthesized from thiourea and α,ω-bromine-terminated PIB in a three-step, one-pot procedure, using a cosolvent system of 1:1 (v:v) heptane: dimethylformamide. The initial alkylisothiouronium salt was produced at 90 °C. Aqueous base hydrolysis at 110 °C resulted in thiolate chain ends, which were re-acidified to form telechelic PIB-SH. 1H and 13C NMR confirmed thiol functionality and complete terminal halogen conversion. Thiol-based "click" reactions were used to demonstrate PIB-SH utility. Alkyne-terminated PIB was synthesized by a phosphine-catalyzed thiol-ene Michael addition with propargyl acrylate. Reaction of this product with 6-mercaptohexanol produced tetrahydroxy-functional PIB by a sequential thiol-ene/thiol-yne procedure. 1H NMR confirmed the structures of both products. PIB-SH was reacted with isocyanates in the presence of base to produce polythiourethanes. A model reaction used phenyl isocyanate in THF with catalytic triethylamine. Similar conditions were used to produce PIB-based thiourethanes with and without a small-molecule chain extender. Increased molecular weights and thiol group conversion were observed with GPC and 1H NMR, respectively. © 2010 Wiley Periodicals, Inc.