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 10(5)-10(7) were characterized by low-angle light scattering and dilute solution viscosity measurements. The weight average molecular weight, M(w), the second virial coefficient, A2, the intrinsic viscosity, [eta], and the Huggins constant, k(H), were determined for all samples using tetrahydrofuran, a marginal to good solvent for the polymer. Determination of [eta] 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 [eta]/M(w)1/2 vs M(w) and then extrapolating to zero molecular weight to obtain the product of the Flory viscosity constant, PHI, 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 PHI determined from many experimental studies, these results lead to a characteristic ratio, C(infinity), of 19 and a Kuhn statistical segment length, l(k), of 5.4 nm. The data in THF are also well represented by a Mark-Houwink-Sakarada equation of [eta] = 0.0170M(w)0.672. Some potential limitations of the Burchard-Stockmayer-Fixman plot and similar methods for obtaining the unperturbed dimensions of a polymer chain are discussed.