Polybutadiene Chain Immobilization in B-Core, Star-Branched SB Block Copolymers

摘要

The equilibrium solubility of gases in a star-branched SB block copolymer can bereliably estimated from a volume fraction weighted average of the homopolymer solubilities; the value of heat of solution of gas in SB block copolymer lies between the two values associated with the constituent homopolymers. Diffusion coefficients for gases in SB block copolymers are bracketed by the homopolymer values over the range of temperature employed, but the activation energies for diffusion in SB are higher than either of the homopolymer values. The anomalous temperature dependence and the inability of a computer stimulation to reproduce experimental diffusion coefficient values for SB supported the concept of a temperature dependent restriction on chain mobility in the polybutadiene regions of the SB block copolymer. This Beta factor has values of about 2-3 at room temperature but decreases to unity when the polystyrene chains become mobile at the polystyrene Tg.