EFFECTS OF SHEAR-FLOW AND ANNEALING ON THE MORPHOLOGY OF RAPIDLY PRECIPITATED IMMISCIBLE BLENDS OF POLYSTYRENE AND POLYISOPRENE

Binary blends of polystyrene (PS) and polyisoprene (PI) were prepared by rapidly precipitating a homogeneous solution, consisting of PS, PI and toluene, into methanol under vigorous agitation. In this study, a series of PSs and PIs were synthesized via anionic polymerization in o ur laboratory. Portions of the as-precipitated blend were annealed at 110 degrees C for different periods up to 12 h and the rest was extrud ed at 160 or 180 degrees C using a capillary die. The extrudates were also annealed for different periods up to 12 h. Then, the morphology o f the as-precipitated blend with and without annealing, and the extrud ate with and without annealing, was investigated using transmission or scanning electron microscopy. We found that: (1) the as-precipitated blend had a co-continuous (or cuasi co-continuous) morphology, often o bserved in two-phase polymer mixtures which have undergone spinodal de composition; (2) annealing or extrusion transformed the initially co-c ontinuous (or quasi co-continuous) morphology of the as-precipitated b lend into a well-defined dispersed two-phase morphology; (3) during an nealing, the elongated droplets in an extrudate specimen recoiled cons iderably, the extent of which depended upon the duration of annealing. The effects of blend composition and the viscosity ratio of the const ituent components on two-phase blend morphology are discussed. Copyrig ht (C) 1996 Elsevier Science Ltd.