Styrene-vinyl pyridine diblock copolymers: Achieving high molecular weights by the combination of anionic and reversible addition–fragmentation chain transfer polymerizations
AbstractAnionic and reversible addition–fragmentation chain transfer (RAFT) polymerizations were combined for the preparation of high molecular weight (MW) amphiphilic diblock copolymers based on the hydrophobic styrene (Sty) and the more polar 2-vinyl pyridine (2VPy) or 4-vinyl pyridine (4VPy). In particular, four amphiphilic Sty-VPy diblock copolymers with MWs up to 271,000 g mol–1 were prepared. For the polymer synthesis, first, living anionic polymerization of Sty using sec-butyl-lithium as initiator in tetrahydrofuran at −70 °C, followed by termination with ethylene oxide were employed for the preparation of OH-functionalized homopolyStys. Subsequently, a modification of the OH-terminal group was performed by the attachment of a 4-cyanopentanoic acid dithiobenzoate chain transfer agent (CTA) group, giving a polySty macroRAFT CTA, which was extended with 2VPy or 4VPy units using RAFT polymerization. Thus, the prepared diblock copolymers comprised a first block which was near-monodisperse in size, and a second more heterogeneous block. All diblock copolymers were characterized in terms of their MWs and compositions by gel permeation chromatography and 1H NMR spectroscopy, respectively, giving results close to the theoretically expected values. Films cast from chloroform solutions of the diblock copolymers were investigated in terms of their bulk morphologies using transmission electron microscopy, which indicated that the minority block consistently formed the discontinuous microphase, spherical or cylindrical.