Solid‐state phase behavior and molecular‐level mixing phenomena in a strongly interacting polymer blend

Abstract

AbstractThis research contribution addresses mixing phenomena in a polymer blend that exhibits strong intermolecular association and bieutectic phase behavior. Molecular‐level observations of specific interactions between dissimilar blend components have been obtained from high‐resolution solid‐state proton and carbon‐13 nuclear magnetic resonance (NMR) experiments at ambient temperature. Results illustrate mixing effects on the isotropic chemical shifts of the critical component in a completely or partially phase‐mixed blend. Perturbations in the NMR spectra result from conformational changes, hydrogen bonding, molecular complexation, or altered packing geometries that occur concomitantly with the mixing process. More convincing evidence that two components of a strongly interacting blend reside in a near‐neighbor environment is obtained from the measurement of proton spin diffusion between dissimilar species. Proton spin diffusion is measured directly via the high‐resolution CRAMPS experiment (Combined Rotation and Multiple Pulse Spectroscopy) in a molecular complex of poly (ethylene oxide) and resorcinol. A primary objective of this research endeavor is to bridge the gap between macroscopic and molecular‐level probes of phase behavior and intermolecular association in mixtures that form molecular complexes. In this respect, the temperature ‐composition projection of the thermodynamic phase diagram is generated for binary mixtures of poly (ethylene oxide) and resorcinol, whose interaction sites are characterized via solid‐state NMR. Under fortuitous conditions that are related to the overall mixture composition, two morphologically and crystallographically inequivalent phenolic 13C NMR signals are identified for resorcinol when the blends exist in a two‐phase region below the eutectic solidification temperature. The success of this proposed structure–property relationship scheme, which bridges molecular‐level mixing phenomena (via NMR) with solid‐state phase behavior (via differential scanning calorimetry) depends on our ability to understand material properties at a level where continuum hypotheses are no longer valid.