Surface and Bulk Phase Separation in Block Copolymers and Their Blends. Polysulfone/Polysiloxane

Abstract

series of polysulfone/polysiloxane alternating block copolymers and their blends with polysulfone. X-ray photoelectron spectroscopy (XPS) with angular dependence was used to obtain the compositional information from the top ~6 nm of the surfaces, and transmission electron microscopy (TEM) was used to characterize the bulk morphologies. In general, solvent-cast neat block copolymers had a layer (>6 nm) at the surface enriched in siloxane and the bulk had 10-50-nm microphase-separated domain structures. In the case of blends, siloxane surface enrichment was relatively high, even at bulk concentrations as low as 0.05% w/w siloxane. The surface siloxane concentration showed a rapid increase between 1 and 10% w/w bulk siloxane concentration, corresponding to the appearance of 0.1-10-μm diameter macrophases of block copolymer in the bulk. The blend surfaces attained surface compositions equivalent to pure copolymer at bulk concentrations above 10% siloxane, where phase inversion occurred in the bulk. XPS results indicated that the polysiloxane block length controlled the level of surface enrichment of siloxane, while the polysulfone block length influenced the gradient of surface composition, or the degree of phase mixing. The relationship between bulk phase separation and surface segregation was elucidated in a. © 1988, American Chemical Society. All rights reserved.