Poly (methylphenyl )silane: Structural Properties S. DEMOUSTIER-CHAMPAGNE, * A. JONAS, † J. DEVAUX Universite ´ catholique de Louvain, Laboratoire de Physique et de Chimie des Hauts Polyme `res, Croix du Sud, 1, B-1348 Louvain-la-Neuve, Belgium Received 26 June 1996; revised 24 January 1997; accepted 30 January 1997 ABSTRACT: The physical structure of poly(methylphenyl)silane (PMPS) has been in- vestigated using wide-angle x-ray scattering at various temperatures and optical polar- izing microscopy. The results obtained by these techniques clearly show the existence of an ordered phase in PMPS. The crystallinity of our sample was estimated to be about 10% at room temperature. Below 190°C, the atactic chains pack into a monoclinic crystalline lattice of near hexagonal symmetry, with two types of disorder existing in the packing. At about 190°C, a phase transition to a liquid crystalline columnar hexagonal packing ( D ho ) occurs. Finally, the sample melts into an isotropic amorphous phase.  1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1727 – 1736, 1997 Keywords: polysilane; microstructure; mesophase; liquid crystal INTRODUCTION tures at room temperature, with many of them un- dergoing transitions to a hexagonal columnar liq- uid-crystalline phase at higher temperature. Simi- Polysilane polymers have attracted considerable at- tention over recent years. This is due in part to their lar structures have been observed on a large range of temperatures for copolymers of di-n -alkylsi- unusual photophysical and electronic properties re- sulting from s-electrons delocalization along the sil- lanes 10,11 as well as for many unsymmetrical poly(di-n -alkyl ) silanes homopolymers such as icon backbone which make them potentially useful for a variety of technological applications. 1,2 One poly( n -butyl-n -hexyl)silane 11,12 or poly-(ethyl-n -bu- tyl ) silane. 13 Poly ( alkylaryl ) silanes, however, have consequence of the Si{Si s-electrons delocalization is that the polysilanes exhibit strong absorption in so far always been described as amorphous poly- mers, with some controversy existing for poly ( meth- the near-ultraviolet region, having excitation energ- ies strongly influenced by the conformation of the ylphenyl ) silane ( PMPS ) . This polymer has indeed been reported by Maxka 14 to be partially crystalline. polysilane backbone. 3–5 In order to study the rela- tionship between the spectroscopic properties and In a recent article 15 we reported the study of the thermal behavior of PMPS by differential the backbone conformation of poly ( di-n -alkyl ) si- lanes, investigations of the structure of many sym- scanning calorimetry ( DSC ) , dynamic mechani- cal thermal analysis (DMTA), and thermome- metrical poly ( di-n -alkyl ) silanes have recently been carried out and reported by several laboratories. 6–9 chanical analysis (TMA). Two rather broad ther- These polymers generally adopt crystalline struc- mal transitions were detected at Ç 95 and 195°C for low molecular weight PMPS. These transitions occurred at higher temperatures for PMPS of Correspondence to: S. Demoustier-Champagne higher molecular weight. The first thermal transi- * Research Assistant of the National Fund for Scientific tion was assigned to a glass transition and the Research ( Belgium) . † Research Associate of the National Fund for Scientific second one to a phase-disordering transition ac- Research ( Belgium) . companied by the softening of the polymer. In or- Contract grant sponsor: Belgian National Fund for Scien- der to provide a more detailed understanding of tific Research  1997 John Wiley & Sons, Inc. CCC 0887-6266/97 / 111727-10 the various phase transitions of PMPS, we have 1727 9606032 / 8q2e$$6032 06-10-97 19:55:52 polpa W: Poly Physics