SYNTHESIS OF LINEAR AND STAR-SHAPED BLOCK-COPOLYMERS OF ISOBUTYLENE AND METHACRYLATES BY COMBINATION OF LIVING CATIONIC AND ANIONIC POLYMERIZATIONS

A new synthetic route for the preparation of polyisobutylene (PIB)-bas ed linear and starshaped block copolymers was developed by combining l iving carbocationic and anionic polymerizations. Living PIB chains wer e quantitatively endcapped with 1,1-diphenylethylene, leading to 1,1-d iphenyl-1-methoxy (DPOMe) or 2,2-diphenylvinyl (DPV) termini, or both. Both the DPOMe- and DPV-terminated PIBs, and the mixtures of both end groups were quantitatively metalated with K/Na alloy, Cs metal, or Li dispersion in THF at room temperature. The resulting stable macrocarba nion obtained by metalation with K/Na alloy was used to initiate livin g anionic polymerization of tert-butyl methacrylate (tBMA) yielding PI B-b-PtBMA block copolymers with nearly quantitative blocking efficienc y. Hydrolysis of the ester groups by HCl in dioxane resulted in amphip hilic polyisobutylene-bloch-poly(methacrylic acid) block copolymers. R eplacing K+ with Li+ by excess LiCl gave a PIB macroinitiator suitable for anionic polymerization of methyl methacrylate (MMA). A series of linear PMMA-b-PIB-b-PMMA block copolymers and of star-shaped PIB-b-(PM MA)(3) block copolymers were successfully synthesized by telechelic PI B macroanions with high blocking efficiencies. Characterizations of th ese new thermoplastic elastomers were carried out by SEC, DSC, dynamic -mechanical, and stress-strain measurements.