Polyisobutylene stars and polyisobutylene-block-poly(tert-butyl methacrylate) block copolymers by site transformation of thiophene end-capped polyisobutylene chain ends

A new synthetic route for the synthesis of polyisobutylene (PIB) stars and PIB-poly(methacrylate) block copolymers was developed by combining living carbocationic and anionic polymerizations. Rapid and quantitative monoaddition of thiophene to living PIB chains has been observed in conjunction with TiCl4 as Lewis acid in n-hexane/CH2Cl2 60/40 v/v at -78degreesC leading to the formation of 2-polyisobutylenyl-thiophene (PIB-T). PIB-T was quantitatively metalated with n-butyllithium in THF at -40degreesC. H-1 NMR spectroscopic and GC studies of the corresponding model compound, 2-(1,1,3,3-tetramethylbutyl)thiophene, clearly verified quantitative metalation. The resulting stable macrocarbanion (PIB-T-,Li+) was used to initiate living anionic polymerization of tert-butyl methacrylate (tBMA) yielding PIB-b-PtBMA block copolymers with high blocking efficiency. PIB stars were prepared via the coupling reaction of the stable macrocarbanion with SiCl4 as a coupling agent. Characterization of these block copolymers and PIB stars was carried out by size exclusion chromatography (SEC), liquid adsorption chromatography at critical conditions (LACCC), and NMR spectroscopy.