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1007-S10-03

Synthesis and Orientation of Poly(dialkylstannane)s Fabien Choffat, Sara Fornera, Paul Smith, and Walter Caseri Department of Materials, ETH Zürich, Zürich, CH-8093, Switzerland

ABSTRACT Polystannanes, i.e. organometallic polymers of the chemical formula (SnR2)n, are relatively little explored, although they belong to the rare examples of polymers which are characterized by a backbone of metal atoms which are linked by covalent bonds. We developed a new synthetic route which yields pure linear poly(dibutylstannane) [Sn(Bu)2]n by polymerization of dibutylstannane (dibutyltin dihydride) with the catalyst [RhCl(PPh3)3]. Here, we report that the conversion and the reaction rate of dibutylstannane depends crucially on the temperature and [RhCl(PPh3)3] is also suited for the polymerization of dioctylstannane and didodecylstannane. The polymers thus obtained were characterized by 1H, 13C and 119Sn NMR spectroscopy: Orientation of all polystannanes was achieved by tensile drawing. The orientation was examined by UV-vis spectroscopy with polarized light and X-ray diffraction. Remarkably, the orientation of the backbone depended on the length of the alkyl groups. INTRODUCTION Relatively few reports describe polymers of the composition (SnR2)n (polystannanes), although compounds with that chemical composition were synthesized already by Löwig in 1852 [1] by reaction of iodoethane with a Sn/K or a Sn/Na alloy, in the presence of quartz sand which was used to control the reaction rate [1]. Remarkably, the conversion of iodoethane with Sn/Na alloy was attributed to a reaction of the Wurtz type as early as 1860 [2,3], which more than 100 years later has also been applied for the preparation of poly(dialkylstannane)s by treatment of dialkyltin dichlorides with sodium [4-6]. The resulting polystannanes were obtained as high molar mass products [6], however, in low yields and with (cyclic) oligomers as byproducts. In the last 15 years, alternative routes for the preparation of polystannanes have been developed, such as electrochemical reactions [7,8] or catalytic dehydropolymerizations of dialkylstannanes, R2SnH2 [9-11]. Unfortunately, the polymers prepared by those methods frequently were not isolated and typically contained significant fractions of cyclic oligomers [10,11]. Recently, however, we demonstrated that Wilkinson’s catalyst was suited for the polymerization of Bu2SnH2, which yielded only linear [Sn(Bu)2]n of high molar mass in high yields, and no detectable amounts of cyclic byproducts [9]. Remarkably, the resulting [Sn(Bu)2]n was found to be in a liquid-crystalline state at room temperature [9] and featured semiconductive

properties as detected with the pulse-radiolysis time-resolved microwave conductivity technique (PR-TRMC) [12]. Here, we report the synthesis and selected properties of a family of linear poly(dialkylstannane)s, as well as their orientation. Because poly(dialkylsilane)s, which show certain structural similarity to polystannanes (a backbone of silicon instead of tin), were reported to be