Effective interaction parameter between branched and linear polystyrene

Values of the effective interaction parameter (X) between regular, long-bra nched polystyrene chains and their linear analogues were measured with smal l-angle neutron scattering for several star-branched chains and one comb-ty pe polymer. The contribution to this interaction due to architecture alone increases monotonically with star functionality for the set of polymers stu died here. The interaction appears to be less sensitive to variations in ar m size than would be expected from fluctuation theory predictions by G. H. Fredrickson, A. Liu, and F. S. Bates (Macromolecules 1994, 27, 2503) for a purely entropic interaction due to architecture. The change in chi with the volume fraction of the star in the blend is in agreement with the theory, however. The magnitudes of the interaction in the star/linear blends are sm all enough that bulk phase separation is unlikely, whereas that in the comb /linear blend is about 20 times higher for the same number of arms. Thus, b ulk phase separation can be readily expected for comb/linear blends at comm ercially relevant values of molecular weights. (C) 2001 John Wiley & Sons, Inc.