SPECIFIC REFRACTIVE-INDEX INCREMENTS OF SEGMENTED POLYURETHANES

Specific refractive index increments nu of polyester-based segmented p olyurethanes in N,N-dimethyl formamide have been determined, and the q uotient d nu/df(d) has been evaluated (where f(d) is the weight factio n of hard-segment units). The results are in good agreement with the v alues calculated from group contributions to the molar refraction, usi ng the Vogel or the Gladstone-Dale equations. The values calculated wi th the Lorenz-Lorentz equation are too low. A potential explanation of this fact is proposed. The same methods have been applied to reported nu values for polyether-based polyurethanes. An explanation is propos ed for differences in d nu/df(d) for polyester- and polyether-based po lyurethanes. (C) 1998 John Wiley & Sons, Inc.