Phase Transitions in Polymer Blends and Block Copolymers Induced by Selective Dilation with Supercritical Co

Supercritical fluids (SCFs) offer a number of advantages for the synthesis and processing of polymeric materials. Early work in the field focused on the high-pressure polymerization of ethylene or exploited the adjustable physicochemical properties of SCFs, including density and dielectric constant, for the fractionation, extraction and impregnation of polymers.' Recently, the field has expanded to include polymer synthesis and modification by reactive processing in the presence of CO 2. With few exceptions these are heterogeneous processes that are facilitated by enhanced transport within the SCF-swollen polymer and are sensitive to the partitioning of solutes between the fluid and polymer phases. Examples include heterogeneous dispersion polymerizations in CO22, condensation reactions in dilated melts', and the preparation of composite materials by conducting chemical reactions directly within solid polymers swollen by CO2.4