Mean-square optical anisotropy of poly(n-hexyl isocyanate) in dilute solution

The mean-square optical anisotropy (Gamma (2)) was determined from anisotro pic light scattering measurements for nine samples of poly(n-hexyl isocyana te) (PHIC), a typical semiflexible polymer, in the range of weight-average molecular weight from 1.65 x 10(4) to 1.04 x 10(5) in n-hexane at 25.0 degr eesC. It was found that the behavior of the ratio (Gamma (2))/x(w) as a fun ction of the weight-average degree of polymerization x(w) may be satisfacto rily explained by the corresponding theory on the basis of the Kratky-Porod wormlike chain model with the respective values 840 Angstrom and 71.5 Angs trom (-1) of the basic model parameters, i.e., the static stiffness paramet er lambda (-1) and the shift factor ML, and also with the assigned value 1. 1(2) Angstrom (2) of the difference Delta alpha between the polarizabilitie s, per unit contour length, parallel and perpendicular to the chain contour . The above value of Delta alpha is appreciably larger than its value 0.5(3 ) Angstrom (2) estimated from the bond polarizabilities on the basis of the chemical structure of PHIC, indicating that there exists definitely some a dditional scattered intensity arising from the effect of collision-induced polarizabilities. However, this does not affect the dependence itself of (G amma (2))/x(w) on x(w). From a comparison of the present results for PHIC w ith previous ones for typical flexible polymers, it is seen that the differ ence in the behavior of (Gamma (2))/x(w) between them arises from that in c hain stiffness.