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 mixing: isothermal cross-polarization/magic-angle-spinning (CP/MAS) dipolar dephasing 13 C NMR, temperature-dependent 13 C CP/MAS NMR, and one-pulse 1 H 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.