Rudolf Faust, Chemistry
The synthesis of poly[(methyl methacrylate-co-hydroxyethyl methacrylate)-b-isobutylene-b-(methyl methacrylate-co-hydroxyethyl methacrylate)] P(MMA-co-HEMA)-b-PIB-b-P(MMA-co-HEMA) triblock copolymers has been accomplished by a site transformation technique from living cationic to living anionic polymerization. This method involved the preparation of DPE end-functionalized PIB, which was quantitatively metalated with n-butyllithium. The resulting macroanion efficiently initiated the living polymerization of methacrylate monomers at –78 °C, yielding di- or triblock copolymers with high blocking efficiency. Anionic copolymerization of MMA and 2-[(trimethylsilyl)oxy]ethyl methacrylate (protected HEMA) resulted in random copolymers The obtained triblock copolymers showed microphase separation evidenced by the two glass transitions at -64 and 120 °C, observed by differential scanning calorimetry (DSC). The block copolymers exhibited stress-strain behavior typical of thermoplastic elastomers. The triblock copolymers are promising candidates for drug eluting cardiovascular stent coatings. The presence of hydroxyl functionality provides an opportunity for further modification.