SOLID-STATE NMR DETECTION OF MOLECULAR MIXING IN BIEUTECTIC BLENDS, D-METAL COMPLEXES, AND PHASE-SEPARATED COPOLYMERS

This research contribution addresses micromixing in polymer blends that exhibit strong intermolecular association. Specific interactions between dissimilar blend components are detected via high-resolution solid state proton and carbon-13 NMR spectroscopy. The isotropic chemical shifts of the critical component provide strong evidence that molecular complexes form. NMR spectral differences between the blends versus the undiluted components arise from crystal structure modifications(if appropriate), conformational changes, hydrogen bonding, d-metal coordination, 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 homogeneous solid solution of poly(ethylene oxide) and resorcinol. and indirectly via the carbon-13 spin system in a modified version of the Goldman-Shen experiment for microphase-separated ionic and tri-block copolymers. One of the primary objectives of this research endeavor is to bridge the gap between macroscopic and site-specific probes of phase behavior and strong interaction in mixtures that form homogeneous solid solutions or coordination complexes. In this respect, results from a macroscopic phase of the polymer-blend research are included in this contribution. Thermal and mechanical properties are measured for strongly interacting systems, whose interaction sites are characterized via solid state NMR. Metal-ligand coordination in blends of nickel acetate with poly(4-vinylpyridine) produces an extraordinary synergistic effect on the glass transition response. The maximum increase in blend T(g) relative to the undiluted polymer is in the order of 100-degrees-C. Coordination between the nitrogen lone pair in poly(4-vinylpyridine) and the zinc cation in DuPont's SURLYN (TM) ionomers produces a 15% enhancement in mechanical fracture stress relative to the undiluted ionomer. The success of our structure -property relationship scheme described herein, which bridges microscopic detection of site-specific interactions (via NMR) with practical macroscopic (DSC and stress strain) measurements, depends upon our ability to understand material properties at a level where continuum hypotheses are no longer valid.