Solution Properties of Poly(di-n-hexylsilane): An Estimate of Its Unperturbed Dimensions

A series of 10 samples of poly(di-n-hexylsilane) spanning a molecular weight range of 106−107 were characterized by low-angle light scattering and dilute solution viscosity measurements. The weight average molecular weight, Mw, the second virial coefficient, A2, the intrinsic viscosity, [n], and the Huggins constant, kH, were determined for all samples using tetrahydrofuran, a marginal to good solvent for the polymer. Determination of [n] in the marginal to poor mixed solvent of 41.3 wt % 2-propanol/hexane was also done for five of the samples. The results were correlated according to the method of Burchard, Fixman, and Stockmayer by plotting [n]/Mw1/2 vs Mw and then extrapolating to zero molecular weight to obtain the product of the Flory viscosity constant,Φ, and (〈 r2〉 0/M)3/2. Here 〈 r2 〉0 is the mean square end-to-end distance of the polymer unperturbed by excluded volume interactions. Using a value of $ determined from many experimental studies, these results lead to a characteristic ratio, C, of 19 and a Kuhn statistical segment length, lk, of 5.4 nm. The data in THF are also well represented by a Mark-Houwink-Sakarada equation of [n] = 0.0170MW0.672. Some potential limitations of the Burchard-Stockmayer-Fixman plot and similar methods for obtaining the unperturbed dimensions of a polymer chain are discussed. © 1991, American Chemical Society. All rights reserved.