Solid-State NMR Studies On The Microdomain Structure, Interactions And Dynamics Of Typical Multiphase Polymer

The design and preparation of multiphase polymer materials is one of the main targets in modern polymer science. The microstructure, miscibility, intermolecular interaction and molecular dynamics of the multiphase polymer system are responsible directly for the material properties. Therefore, they have been the basic problems and attracted significant attention in polymer physics. In this thesis, a variety of solid-state NMR methods and a new developed NMR technique by our group, in combination with the quantum chemical calculations were utilized to investigate the miscibility, domain size, interphase thickness, intermolecular interaction and molecular dynamics for two kinds of multiphase polymer systems. They are styrene-butadiene copolymers with the same volume percent and different molecular architectures, and poly (methyl methacrylate) (PMMA) and poly (4-vinyl phenol) (PVPh) hydrogen-bonded polymer blends prepared under different conditions.1H spin diffusion solid-state NMR, in combination with other techniques, was utilized to investigate the effect of molecular architecture and temperature on the interphase thickness and domain size in poly (styrene)-block-poly (butadiene) and poly (styrene)-block-poly (butadiene)-block-poly (styrene) copolymers (SB and SBS) over the temperature from 25℃to 80℃. These two block copolymers contain equal PS weight fraction of 32 wt%, and especially, polystyrene (PS) and polybutadiene (PB) blocks are in glass and melt state, respectively, within the experimental temperature range. It was found that with increasing temperature the domain sizes of the dispersed phase and interphase thicknesses in these two block copolymers increased. Surprisingly we found that the interphase thicknesses in these two block copolymers were obviously different, which was inconsistent with the theoretical predictions about the evolution of interphase in block copolymer melts by self-consistent mean-field theory (SCFT). This implies that the interphase thickness not only depends strongly on the binary thermodynamic interaction (χ) between the PS and PB blocks, but also is influenced by their molecular architectures in the experimental temperature range. These results provide new insights into the theory of polymer physics for the microphase separation of block polymers.In combination with quantum chemical calculations, a variety of advanced multi-scale solid-state NMR techniques were used to investigate the microstructure and dynamics in PMMA/PVPh polymer blends. First, a new chemical-shift filtered high-resolution NMR pulse sequence based on a recently developed continuous phase modulation technique was proposed to characterize the microphase structure and miscibility in rigid/rigid polymer blends. The miscibility and domain sizes of the samples with different treated conditions were well elucidated by this new NMR technique combined with spin-diffusion experiments and the numerical simulation for the spin-diffusion process. Second, the possible hydrogen-bonding interactions between the carbonyl group of PMMA and hydroxyl group of PVPh were successfully elucidated by two-dimensional 1H-1H spin-exchange and 13C-1H heteronuclear chemical-shift correlation (HETCOR) NMR experiments at different mixing time. Furthermore, the 13C 2D SUPER experiments were applied to determine chemical shift anisotropy-separation of undistorted powder patterns and quantum chemical calculations for the theoretical predictions of CSA parameters were utilized to investigate the intermolecular hydrogen-bonding interactions and molecular conformation of the blends. The chemical shift and conformation predicted by quantum chemical calculations were confirmed by solid-state NMR experiments. A possible interaction model of the blends was proposed. Finally,13C-1H polarization inversion and spin exchange at magic angle (PISEMA) experiments at different temperature were used to reveal the heterogeneous dynamics resulting from the cooperative motion associated with the hydrogen bonding interaction. It provides clear evidence that the motion of aromatic group in PVPh is affected by the rotating motions of methyl in PMMA for both the annealed powder blend at 120℃and cast film sample at room temperature. In addition, with increasing temperature the local mobility of the cast film sample increases.