SYNTHESIS, CHARACTERIZATION, GLASS-TRANSITION BEHAVIOR, AND THE ELECTRONIC-STRUCTURE OF HIGH-MOLECULAR-WEIGHT, SYMMETRICALLY SUBSTITUTED POLY(FERROCENYLSILANES) WITH ALKYL OR ARYL SIDE-GROUPS

A series of high molecular weight, symmetrically substituted poly(ferrocenylsilanes) [Fe(eta-C5H4)2(SiR2)]n (2a-e: a, R = Me; b, R = Et; c, R = Bu; d, R = Hex; e, R = Ph) have been prepared via the thermal ring-opening polymerization of the corresponding strained cyclic ferrocenylsilane monomers Fe(eta-C5H4)2(SiR2)(la-e). The latter species were prepared via the reaction of dilithioferrocene/TMEDA(TMEDA = tetramethylethylenediamine) with the appropriate symmetrically substituted dichloroorganosilane R2-SiCl2. Polymers 2a-d were structurally characterized by H-1, C-13, and Si-29 NMR, UV/visible spectroscopy, and elemental analysis. The molecular weights of polymers 2a-d were estimated by gel permeation chromatography using polystyrene standards. Polymer 2e was found to be insoluble in common organic solvents and was characterized by solid-state NMR. In addition, the solution behavior of [Fe(eta-C5H4)2-(SiBu2)]n (2c) was investigated by low-angle laser light scattering which yielded an absolute value of M(w)BAR = 2.29 X 10(5) and a second virial coefficient, A2 = 1.3 X 10(-4) mol cm2 g-2 in THF at 20-degrees-C. The glass transition behavior of the poly(ferrocenylsilanes) 2a-d was investigated by differential scanning calorimetry and dynamic mechanical analysis. Glass transition temperatures varied with the substituents present and were found in the range of -26-degrees-C (for polymer 2d) to +33-degrees-C (for polymer 2a). No evidence for melting transitions was detected for the polymer samples studied. UV/visible spectra of polymers 2a-d were measured in THF in the 200-800-nm range and were found to be consistent with an essentially localized electronic structure for the polymer backbone.