CHARACTERIZING DOMAIN MIXING EFFECTS IN HYDROGEN BOND-COMPATIBILIZED POLYMER BLENDS

The nature and extent of phase mixing in blends of hydroxyl-functional ized polystyrene and poly (ethyl acrylate) (PS / PEA), where the drivi ng force for mixing is hydrogen bonding, are characterized by several techniques. Small-angle x-ray scattering (SAXS) shows a reduction in a verage domain size with increasing functionalization level, a result a lso evident from scanning electron microscopy (SEM). Together, the two techniques reveal a very broad distribution of domain sizes. At high functionalization levels, both SAXS and SEM indicate a high degree of ''in-domain'' mixing, with little or no pure PS or PEA remaining in th e blends. Mathematical modeling of dynamic mechanical thermal analysis (DMTA) data is employed to quantify this progression. Initially, mixi ng is primarily interfacial, but as the functionalization level increa ses, the mixed interphase rapidly grows to occupy the entire material. In agreement with the SAXS and SEM results, DMTA modeling shows that further increases in the functionalization level suppress the amplitud e of composition variations in the sample. The onset of extensive in-d omain mixing coincides with the marked changes in stress-strain behavi or observed previously in these materials. (c) 1994 John Wiley & Sons, Inc.