Characterization of poly(di-n-hexylsilane) in the solid state: I. X-ray and electron diffraction studies.

The solid-state structure of poly(di-n-hexylsilane) - a new polymer with highly interesting electronic and photochemical properties -- is shown to consist at room temperature of two polymorphs (an ordered Phase I and a disordered Phase II) whose relative proportions can be varied greatly by means of crystallization and annealing treatments. The intriguing thermochromic transition of this polymer at ~42C results from transformation to a variant of Phase II in which the polysilane chains are packed with high intermolecular order in a pseudohexagonal lattice (alpha=1. 55 nm), while the hexyl side chains become disordered but remain preferentially transverse to the Si-backbones.