Three asymmetrically substituted methyl-alkyl-substituted polysilanes, poly
(methyl-n-propyl)silane, poly(methyl-n-butyl)silane, and poly(methyl-n-hexy
l)silane, have been studied using conventional X-ray ray diffraction and di
rect measurements of the local structure (through a pair correlation functi
on analysis) in combination with UV absorption spectroscopy. These data uni
versally support Si backbone models which are dominated by the presence of
mixed transoid (T), deviant (D), and, possibly, ortho (O) conformations wit
h dihedral angles approximating +/- 170 degrees, +/- 155 degrees, and +/- 9
0 degrees, respectively. There is no evidence for a significant fraction of
all-anti (A, i.e., trans-planar), all-transoid, or anti-gauche conformers.
Crystalline poly(methyl-n-hexyl)silane incorporates a D/T-based Si backbon
e, and this, locally, approximates a D+T+D-T-motif. Poly(methyl-n-hexyl)sil
ane displays a number of low-temperature polymorphic structures, and one of
these is found to exhibit Bragg-like scattering features. Temperature-depe
ndent UV absorption measurements of poly(methyl-n-hexyl)silane resolve two
distinguishable isosbestic points and are indicative of mesomorphic behavio
r.