Core-shell cylinder morphology in poly(styrene-b-1,3-cyclohexadiene) diblock copolymers

A microphase-separated core-shell cylinder morphology has been observed, vi a transmission electron microscopy and small-angle X-ray scattering, in dib lock copolymers of polystyrene (PS) and poly(1,3-cyclohexadiene) (PCHD). Th e structures consist of PS cylindrical cores surrounded by PCI-ID cylindric al annuli which are then hexagonally packed in a matrix of PS. The material s were produced by anionic polymerization of styrene followed by 1,3-cycloh exadiene. Characterization by size exclusion chromatography revealed a main peak due to diblock with a vet-Si narrow molecular weight distribution. Ho wever, a significant amount of PS homopolymer (about 30%) was present in th e as-synthesized materials. The as-synthesized materials with homopolymer p resent produced core-shell morphologies, and these structures became much m ore regular when the homopolymer uas removed by fractionation. After fracti onation, the pure core-shell forming diblocks had PCHD volume fractions of around 0.37 and polydispersities well under 1.1.