Structure Elucidation of Crystalline Poly(diphenylsiloxane)

Abstract

This study shows that the structure of the poly(diphenylsiloxane) (PDPhS) backbone is quasi-planar rather than helical. The nearest-neighbor chains in the crystal are packed in a hexagonal configuration. Using molecular mechanics calculations and analysis of X-ray powder diffraction data, it has been determined that the crystalline structure of PDPhS has Pbn2\ symmetry and the backbone consists of siloxane bonds in a quasi cis-trans sequential conformation. The deviation of each bond from the planar configuration is about 15°. The backbones of the two chains in the unit cell are antisymmetrical. The Si-O-Si bond angle is 145°and the torsional angles of the vicinal phenyl groups relative to each other are 125 and 72°. The orientation of the phenyl groups in the crystal consists of parallel and perpendicular nearest neighbors. The calculated X-ray results are able to explain the main features of the experimental pattern in terms of position and intensity of the peaks. Molecular mechanics calculations suggest that the density of ideal crystals of poly(diphenylsiloxane) at low temperatures should be in the range 1.26-1.3 g/cm3, whereas the reported experimental value is 1.22 g/cm3. A new set of molecular mechanics parameters for the UFF method to more accurately describe polysiloxanes in the condensed state is given.

An X-Ray Diffraction Study on Crystalline and Mesomorphic Structures of Poly(diethylsiloxane)

“…The most probable fractional atomic coordinates are shown in Table IV. It should be noticed again that the dynamical jump-like motion for ethyl side chains is reported to occur in /3 2 -PDES as the fact that only two signals were observed in MAS 13 C NMR spectrum for /3 2 -PDES. 5 Therefore, the finally refined structure for the side chains, i.e., the positions of the methyl groups depicted in Figure 2, should be the averaged one.…”

“…2 The conformational stability for the planar backbone is also examined by molecular mechanics calculation of isolated PDES chain by Miller et al 14 By combined use of molecular modeling method and X-Ray powder diffraction pattern, Grigoras et al investigated structure analysis of crystalline poly(diphenylsiloxane). 13 The backbone conformation is determined as quasi cis-trans conformation, which is same as the proposed conformation for PDES. For other homologues of PDAS, only the X-Ray powder diffraction patterns and limited results of structural analysis have been reported.…”

Chemical Degradation Pathways in Siloxane Polymers Following Phenyl Excitations

“…In these cases, the modeled polymer strand is noninteracting with any possible neighboring strands. For reference, the equilibrium L z for a pure PDPS crystal with the same number of monomer units (i.e., 12) is ≈3.0 nm . Condensed phase configurations were generated by isotropically straining the cell to cubic dimensions with side lengths 1.57, 1.42, 1.32, and 1.24 nm, which yield systems with densities 0.6, 0.8, 1.0, and 1.2 g cm –3 .…”

Fundamental Aspects of Aminoalkyl Siloxane Softeners by Molecular Modeling and Experimental Methods

“…The full modified force field parameters were presented in another report [7]. The partial charges of the atoms of a polymer and a cotton came from the charge equilibration method [ 15].…”

“…In addition, we used the van der Waals parameters de-veloped by Lii and Allinger [ 10] for the carbon and hydrogen atoms in the phenyl rings and hydrocarbons. The full modified force field parameters were presented in another report [7]. The partial charges of the atoms of a polymer and a cotton came from the charge equilibration method [ 15].…”