Dynamics of polymer blends and NMR relaxation in solids

Abstract

I investigated the relations among dynamics, structure, and miscibility for three kinds of miscible polymer blends: Poly(2-hydroxyethyl methacrylate)/poly (methacrylic acid) (PHEMA/PMAA), poly (methacrylic acid)/poly (vinyl acetate) (PMAA/PVAc), and polystyrene/poly(vinyl methyl ether) (PS/PVME), using the high-resolution solid-state 13C cross-polarization magic-angle spinning (CPMAS) NMR technique. For the PHEMA/PMAA blends, the hydrogen bonding between side-chain OH of PHEMA and COOH of PMAA causes the molecular motion of PHEMA in the blends to be slow. This was suggested by the temperature dependence of 1H spin-lattice relaxation time in the rotating frame (T1pH, and 13C CPMAS NMR spectra. Furthermore, the inter-polymer dehydration between the side-chain end groups of PHEMA and PMAA after heat treatment at 573 K for 10 min is found by 13C spin-lattice relaxation curve and 13C CPMAS NMR spectral analysis. For the PMAA/PVAc blends, each signal decomposed from a complicated signal at carboxyl and carbonyl region using the five Gaussian curves is assigned by the composition dependence of 13C spin-lattice relaxation time and the relative integrals. For the PS/PVME blends, observed multi-exponential T1pH curves are successfully simulated with insufficient 1H spin-diffusion rate by assuming a three-spin system. The disagreements among the observed T1pH curves are explained as due to the very fast molecular motion of PVME, which causes the 1H spin diffusion to be insufficient between PS and PVME.