Synthesis and characterization of polystyrene-b-poly(1,2-isoprene-ran-3,4-isoprene) block copolymers with azobenzene side groups

Polystyrene-b-poly(1,2-isoprene-ran-3,4-isoprene) block copolymers with azobenzene side groups were synthesized by the esterification of azobenzene acid chloride with polystyrene-b-hydroxylated poly(1,2-isoprene-ran-3,4-isopenre) block copolymers for creating new photochromic materials. The resulting block copolymers with azobenzene side groups were characterized for structural, thermal, and morphological properties. IR and NMR spectroscopies confirmed that the polymers obtained had the expected structures. Differential scanning calorimetric measurements by heating runs clearly showed the glass transitions of polystyrene and polyisoprene main chains and two distinct first-order transitions at temperatures of azobenzene side groups around 48 and 83 degreesC. The microstructure of these block copolymer films was investigated using both transmission electron microscopy (TEM) and near-field optical microscopy (NOM). TEM images revealed typical microphase-separated morphologies such as sphere, cylinder, and lamellar structures. The domain spacing of microphase-separated cylindrical morphology in the NOM image agreed with that of the TEM results. (C) 2002 Wiley Periodicals, Inc.