Synthesis and characterization of poly(methyl methacrylate-co-hydroxyethyl methacrylate)-b-polyisobutylene-b-poly(methyl methacrylate-co-hydroxyethyl methacrylate) triblock copolymers

The synthesis of poly[(methyl metbacrylate-co-hydroxyethyl methaerylate)-b-isobutylene-b-(methyl methacrylate-co-hydroxyethyl methacrylate)] P(MMA-co-HEMA)-b-PIB-b-P(MMA-co-HEMA) triblock copolymers with different HEMA/MMA ratios has been accomplished by the combination of living cationic and anionic polymerizations. P(MMA-co-HEMA)-b-PIB-b-P(MMA-co-HEMA) triblock copolymers with different compositions were prepared by a synthetic methodology involving the transformation from living cationic to anionic polymerization. First, 1, 1 -diphenylethylene end-functionalized PIB (DPE-PIB-DPE) was prepared by the reaction of living difunctional PIB and 1,4-bis(1-phenylethenyl)benzene (PDDPE), followed by the methylation of the resulting diphenyl carbenium ion with dimethylzinc (Zn(CH3)(2)). The DPE ends were quantitatively metalated with n-butyllithium in tetrahydrofuran, and the resulting macroanion initiated the polymerization of methacrylates yielding triblock copolymers with high blocking efficiency. Microphase separation of the thus prepared triblock copolymers was evidenced by the two glass transitions at - 64 and + 120 degrees C observed by differential scanning calorimetry. These new block copolymers exhibit typical stress-strain behavior of thermoplastic elastomers. Surface characterization of the samples was accomplished by angle-resolved X-ray photoelectron spectroscopy (XPS), which revealed that the surface is richer in PIB compared to the bulk. However, a substantial amount of P(MMA-co-HEMA) remains at the surface. The presence of hydroxyl functionality at the surface provides an opportunity for further modification.