Influence of segmental swelling of an asymmetric block copolymer on the morphology of melt-mixed immiscible polymer blends

We investigate the influence of an asymmetric PS-b-PMMA block copolymer (bc p) on the morphology of melt-mixed immiscible binary polymer blends contain ing poly(styrene-co-acrylonitrile) random copolymer (SAN) and poly(cyclohex ylmethacrylate) (PCHMA). By varying the SAN copolymer composition, the bala nce between the swelling of each block segment located at the interface bet ween the two phases is altered and the effect on blend morphology is studie d. As in earlier studies using a symmetric bcp, we find that for a specifie d shear history, there is a zone of effective emulsification of the blend b ounded by regions of internal and external emulsification failure. However, the locations of the boundaries between stable and unstable emulsification differ for an asymmetric versus a symmetric bcp. Thus the morphology depen ds not only on the segmental swelling ratio but also on the difference in t he effective size of each bcp segment. Scaling arguments successfully corre late the limits of stable emulsification for both symmetric and asymmetric bcp. (C) 2000 Elsevier Science Ltd. All rights reserved.