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Solid state NMR of PS/PVME blends, twin liquid crystal polymers and silarylen-siloxane copolymers
Abstract
Thermally induced phase separation in PS/PVME blends was studied by solid state NMR. The proton spin-lattice relaxation in both laboratory and the rotating frame were measured for the entire range of blend composition. Under conditions in which the blends are said to be compatible by other techniques, T$\sb{1\rho}\sp{\rm H}$ results obtained at -5$\sp\circ$C showed the fluctuation of local composition at a ten-angstrom scale. T$\sb{1\rho}\sp{\rm H}$ values at room temperature are closer to the longer relaxation time of PS than expected from simple weighted average of the relaxation times of the constituent homopolymers. This indicates incomplete averaging by spin diffusion and a restraining effect of PS on segmental motions of PVME. The blends were heated to cause phase separation and quenched. From the biphasic decay of $\sp{13}$C magnetization, the compositions of the separated phases were estimated to give a lower critical solution temperature phase diagram. NMR relaxation in PVME blends with PS molecular weight of 9K, 100K and 900K were compared. The mobility of the mesogenic group and the spacer in a series of twin liquid crystal polymers has been investigated by studying the cross polarization constant and the line width of $\sp{13}$C spectrum. Both moieties are found immobile in the crystalline state. The mesogenic group retains its rigidity while the spacer becomes mobile in the mesophase. The mobility of both moieties increases dramatically in the isotropic state. The mobility of the Si nuclei in a series of silarylene-siloxane copolymers has been investigated by studying $\sp{29}$Si NMR relaxation time. There is a correlation between the backbone mobility and the glass transition temperature. The lower the Tg, the more mobile is the molecule. The relaxation profiles for two of the samples can be superimposed by normalizing the free volume effect. The relaxation is dominated by the dipole-dipole interaction between Si and H.
Subject Area
Physical chemistry|Polymer chemistry|Chemistry
Recommended Citation
Chu, Cheng-Wu, "Solid state NMR of PS/PVME blends, twin liquid crystal polymers and silarylen-siloxane copolymers" (1990). Doctoral Dissertations Available from Proquest. AAI9110117.
https://scholarworks.umass.edu/dissertations/AAI9110117