Poly(methacrylic acid)-l-polyisobutylene:: A novel polyelectrolyte amphiphilic conetwork

For the first time, a reliable procedure for synthesizing new acidic polyelectrolyte-containing amphiphilic conetworks (APCNs), poly(methacrylic acid)-l-polyisobutylene (PMAA-l-PIB), is described. The thorough characterization of the synthesis products is also presented through elemental analysis, differential scanning calorimetry (DSC), and basic swelling studies. Three series of APCNs were successfully synthesized in wide composition ranges by the macromonomer method using exact bifunctional methacrylate-telechelic PIB cross-linkers (MA-PIB-MA) of three different molecular weights (M-n): 2000, 5000, and 13000. The MA-PIB-MA macromolecular cross-linkers were prepared via quasiliving carbocationic polymerization. To prevent phase separation and thus insufficient network formation during synthesis, the conetworks were synthesized by thermally initiated free radical copolymerization of MA-PIB-MA and trimethylsilyl methacrylate, a hydrophobized precursor of methacrylic acid. After the next critical synthetic step, the quantitative hydrolytic cleavage of the trimethylsilyl groups from the poly( trimethylsilyl methacrylate) chains in the resulting precursor conetworks, 5-8 different compositions of each PMAA-l-PIB conetwork series were obtained. The low amounts of extractables (< 8-10%) and elemental analysis data showed high copolymerization yields and close to target compositions. DSC investigations indicated phase separation of the PMAA and PIB components. As all PMAA-l-PIB conetworks are optically clear materials, the extent of phase separation must occur on the nanometer scale. The amphiphilic character of these new materials was demonstrated by uniform swelling of PMAA-l-PIB conetworks in both aqueous and apolar media which indicates cocontinuous nanophasic morphology.