Polysilane phase behavior

S. Demoustier-Champagne and J. Devaux, Thermal properties and phase behavior of polysilanes , in Reference 4, pp. 553-574. 

Phase Behavior of -Alkyl-Substituted Polysilanes Christian Mueller, Christine Peter, Holger Frey, and Claudia Schmidt 12.1 Introduction... 

Si, P) have also been used to probe the structures, conformations, phase behavior, and orientations of solid polymers. In this regard, the N NMR observations of crystalline nylons by Murthy and co-workers [51, 52] and the Si NMR observations of the thermo- and piezochromic polysilanes by Schilling and co-workers [53-58] are particularly noteworthy. In chapter 6, many of the same high resolution techniques are used to probe the mobilities of polymer chains in solid samples. 

Silicon Chemistry, ed. P. Jutzi and U. Schubert, Wiley-VCH Verlag GmbH Co. KGaA, Weinheim, Germany, 2003 R 261 C. Mueller, C. Peter, H. Frey and C. Schmidt, Phase Behavior of n-Alkyl-Substituted Polysilanes , p. 159... 

With this new information in mind, an interpretation of the thermochromic behavior of polysilanes in solution can be outlined. We can begin with two calibration points (1) The polymers ( -butyl2Si) and ( -pentyl2Si) absorb at 315 nm both in the solid state and in solution both polymers as solids are known to have an all-D conformation, with co 154°. (2) The well-studied polymer ( -hexyl2 Si) , in its low-temperature phase, absorbs at 375 nm and has a (nearly) all-A conformation. Values of A,nax between 315 and 375 nm should correspond to intermediate values of the average torsional angle, ox... 

In the solid state, polysilanes present a far more complicated picture than in solution. Many different phases may be possible for a single polymer, and the transformations between them may be slow, so that the conformation and spectroscopic behavior often depends on the thermal history of the sample. In partial compensation, additional techniques for studying the polysilanes become available for the solids, especially X-ray scattering. Nevertheless the conformations and structures of solid polysilanes are not well understood. 

Experiments on polysilanes with asymmetric side chain substitution, P45S and P56S, showed no spectacular results, but the behavior of these polymers fits well into the overall picture. P45S has one transition at 319 K and a 3 backbone conformation pressure-induced additional phases were not observed. P56S shows two transitions at 271 and 289 K, even at ambient pressure, indicating two different modifications, probably with 2 and 1 backbone conformations. 

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