PROTON NMR-STUDY OF THE INTIMACY OF MIXING IN A HYDROGEN-BONDED BLEND OF POLYSTYRENE AND POLY(BUTYL METHACRYLATE)

High-resolution solid-state proton NMR techniques were used to examine the mixing of polystyrene (PS) and poly(butyl methacrylate) (PBMA) chains in a blend where the PS was chemically modified by copolymerization with 1.5 mol % of a modified styrene monomer containing a hydroxyl group. Substitution of this modified PS(OH) polymer "compatibilizes" the otherwise incompatible PS/PBMA blend. Proton spin diffusion techniques were used to examine the level of mixing. Data indicated that there is compositional heterogeneity remaining in this 60/40 PS(OH)/PBMA blend on the 6-12-nm scale, a scale which is comparable to the mean separation between "decorations" on the unperturbed Gaussian PS chain. The compositional heterogeneity is such that the mean PS(OH)-proton fraction in the PS(OH)-rich regions is about 75% and likewise for the PBMA-proton fraction in the PMBA-rich regions. The level of mixing is deemed sufficiently intimate for imparting intermediate material properties to this blend. There is also evidence of some molecular-level mixing in the differential line broadening/line narrowing of PBMA/PS(OH) resonances in the blend spectrum.