A new synthetic route for the preparation of polyisobutylene (PIB) based block copolymers was developed by combining living carbocationic and anionic polymerizations. Living PIB chains were quantitatively end-capped with 1,1-diphenylethylene (DPE) leading to 1,1-diphenyl-1-methoxy (DPOMe) and/or 2,2-diphenylvinyl (DPV) termini. This end-capping process is very sensitive to temperature, and retroaddition of DPE occurs in an equilibrium reaction above about -70°C. Both the DPOMe and DPV terminated PIBs, and the mixtures of the two endgroups were quantitatively metalated with K/Na alloy, Cs metal and Li dispersion in THF at room temperature. 1H NMR studies of the corresponding model compounds, 3,3,5,5-tetramethyl-1,1-diphenylhex-1-ene (DPV) and 1-methoxy-3,3,5,5-tetramethyl-1,1-diphenylhexane (MDPE) clearly verify the quantitative degree of metalation. The resulting stable macrocarbanion obtained by metalation with K/Na alloy was used to initiate living anionic polymerization of tert-butyl methacrylate (tBMA) yielding PIB-b-PtBMA block copolymers with nearly quantitative blocking efficiency. Hydrolysis of the ester groups by HCl in dioxane resulted in amphiphilic poly(isobutylene-b-methacrylic acid) block copolymers. Replacing K+ with Li+ by excess LiCl gave a PIB macroinitiator suitable for anionic polymerization of methyl methacrylate (MMA). A series of PMMA-b-PIB-b-PMMA block copolymers was successfully synthesized by telechelic PIB macroanions with high blocking efficiencies. Characterizations of these new thermoplastic elastomers were carried out by SEC, DSC, dynamic-mechanical, and stress-strain measurements.
|Number of pages||14|
|Journal||ACS Symposium Series|
|Publication status||Published - Dec 1 1998|
ASJC Scopus subject areas
- Chemical Engineering(all)