NMR study of the morphology of polystyrene linear/microgel blends

The morphology of blends of polystyrene (PS) microgels with linear PS were studied using NMR spectroscopy. Three techniques were employed to assess the intimacy of mirdng: isothermal;cross-polarization/magic angle-spinning (CP/MAS) dipolar dephasing C-13 NMR, temperature-dependent 13C CP/ MAS NMR, and one-pulse H-1 MAS NMR. The experimental data reveal that linear PS can penetrate: the core of soft microgels, whose network strands are substantially larger than the linear chains. However when the microgel is highly cross-linked, such penetration is prevented. These results are in accord with Flory-Huggins swelling theory. Blends of linear PS with highly cross-linked microgels yield thermodynamically stable morphologies, in which the components are molecularly dispersed, yet segmental contacts are virtually absent. Such a phase morphology is novel and cannot be obtained with-conventional polymer blends.