Polymorphism of poly(di-n-pentylsilane)

We have studied the solid state structure of a low molecular weight (M w = 46 000) poly(di-n-pentylsilane) sample and its dependence on temperature using wide angle X-ray diffraction, DSC and Raman spectroscopy. The results suggest that domains of two distinct structures are present, one having an all-trans conformation and the other a 1/3 helical conformation. The all-trans conformation was observed (even at room temperature) in samples cooled previously to -15°C. Characteristic resonance enhancement of certain Raman vibrations is observed for the planar zigzag polymorph. The all-trans material converts to a 7/3 helical structure at 35°C and subsequently undergoes an order/disorder transformation at about 56°C