STRUCTURE AND PROPERTIES OF POLY(N-PENTYL-N-ALKYLSILANES) .2.

The solid-state electronic properties and structures of poly(n-pentyl- n-hexylsilane) (C5-C6), poly(n-pentyl-n-octylsilane) (C5-C8), and poly (n-pentyl-n-dodecylsilane) (C5-C12) have been investigated using UV ab sorption, differential scanning calorimetry, and X-ray diffraction. At low temperatures, C5-C6 is semicrystalline with an all-trans backbone conformation. Upon heating, it transforms to the hexagonal, columnar, condis crystalline phase observed in many polysilanes. C5-C8 exhibits the hexagonal, columnar mesophase both above and below its first-orde r transition temperature of -32 degrees C. This type of behavior is fo und to be characteristic of poly(n-alkyl-n-alkyl'silanes) with a side- chain asymmetry of two or three carbon atoms, The existence of first-o rder transitions and the observation of UV thermochromic red shifts up on cooling for these polymers which do not crystallize are most likely the result of polarization interactions between the a-bonded silicon backbone and the alkyl side chains, which is consistent with the predi ctions of the model of Schweizer for conjugated polymers.