Structural ordering of two-component hyperbranched copolymers

Polystyrene/polyisoprene (PS/PI) two-component hyperbranched copolymers composed of PS star molecule as the first-generation core were prepared by living anionic polymerization technique: PI branches were comb-likely grafted from the peripheral sites of PS star molecule as the first-generation core. The microphase-separated structures of such hyperbranched copolymers were studied by means of transmission electron microscopy and small-angle X-ray scattering. The hyperbranched copolymers composed of asymmetric composition (PS volume fraction φPS=0.25) formed a lattice of body-centered cubic structure in benzene near the overlap threshold (C*). Such cubic lattice changed to cylindrical structure in the bulk film. Thus this hyperbranched polymer led to the order–order transition from cubic lattice to cylindrical structure in the process of film formation. The hyperbranched copolymers composed of symmetric composition (φPS=0.43) and asymmetric composition (φPS=0.20) showed lamellar and spherical morphologies in the bulk film, respectively. These microphase separation behaviors were very similar to those observed in (AB)n star copolymers.