Solid-State 29Si NMR Analyses of the Structure and Dynamics of Solid Poly(di-n-alkylsilane)s (FUNDAMENTAL MATERIAL PROPERTIES-Molecular Dynamic Characteristics)

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Solid-state 29Si NMR analyses of the solid structure and dynamics have been performed for poly(di-n-butylsilane) with the order-disorder transition at 76 °C. 29Si chemical shift anisotropy (CSA) spectra are measured with an ultraslow magic angle spinning at a rate less than 100 Hz. Almost rigid CSA spectra for the 7/3 helical structure are observed below the transition temperature. In contrast, axially symmetric CSA spectra with different principal values appear above the transition temperature, suggesting the onset of the rotational motion around the molecular chain axis with trans-rich conformation. The changes of the conformation and dynamics around the transition are also discussed for other poly(di-n-alkylsilane)s such as poly(dimethylsilane) and poly(di-n-hexylsilane).