A. Turetskii et al., STRUCTURAL TRANSFORMATIONS IN POLY(DI-N-ALKYLSILOXANE)S WITH ALKYL SIDE-GROUPS CONTAINING 7 TO 10 CARBON-ATOMS, Polymer, 36(6), 1995, pp. 1303-1308
Temperature dependent X-ray diffraction studies of poly(di-n-alkylsilo
xane)s substituted with side chains containing 7 to 10 carbon atoms ha
ve been carried out in order to elucidate the crystalline structure of
these materials. In contrast to their lower substituted homologues, n
o evidence for the presence of a hexagonal columnar mesophase could be
found for the investigated materials. At low temperatures, far below
the melting temperature, the polysiloxane backbones are assumed to pac
k in an orthorhombic lattice, with the n-alkyl side chains in a planar
all-trans conformation and oriented perpendicularly to the backbone.
The paraffinic n-alkyl side chains were found to crystallize in an ort
horhombic lattice. The thermal behaviour of the investigated materials
has been observed to show an odd-even effect. Whereas poly(di-n-hepty
lsiloxane) and poly(di-n-nonylsiloxane) were found to melt in a single
step, an intermediate state of order was observed for poly(di-n-octyl
siloxane) and poly(di-n-decylsiloxane) upon heating from the crystalli
ne to the isotropic state. For this intermediate state, a pseudohexago
nal packing of the n-alkyl side chains is proposed.