evaluating the model parameters (Kuhn segment length X"1, relative molecular mass per unit contour length ML, and chain diameter d) from the intrinsic viscosity data for stiff-chain polymers. Accordingly, the plot of (M2/b])1/3 vs. M112 is linear, and the random-coil value of (R02)/M, i.e., ((fi02)/ML, is simply evaluated from the slope of the plot. The possibilities of estimating ML and d, either from the intrinsic viscosity data alone or, preferably, from their combination with the partial specific volume of the polymer, are discussed. The procedures are applied to nine typical stiff-chain polymers (polyisocyanate, cellulose trinitrate, polypeptides in helical conformation, aromatic polyamides, etc.). The results agree well with those obtained by more involved procedures. The effect of the excluded volume on the shape of the plot is also qualitatively discussed.

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Time-dependent phase separationhransition was observed in aqueous solutions of poly(N-isopropylmethacrylamide) in the temperature range 38-42 "C. The time before the second phase appears is a function of temperature and may reach up to several hours.

SynopsisFractions of two cellulose tricarbanilate samples were characterized by light-scattering (weight-average molecular weight, second virial coefficient, mean-square radius of gyration), gel permeation chromatography (polydispersity index), and viscometry (intrinsic viscmity) in tetrahydrofuran and acetone. The intrinsic viscosity data were analyzed in terms of the theory developed for the continuous wormlike cylinder model, and the chain parameters (Kuhn statistical segment length A-', chain diameter d , and shift factor M,,) were evaluated. The molecularweight dependence of the mean-square radius of gyration in tetrahydrofuran was calculated for the Kratky-Porod chain model and compared with the experimental results. Data on the intrinsic viscosity and radii of gyration for other solvents a t temperatures from 0 to 100°C were analyzed in the same way, and the effects of solvent and temperature on the statistical segment length were evaluated. Polymer-solvent interaction parameters were estimated from the second virial coefficients.*Dedicated to J. Pouchlj. on the occasion of his 60th birthday.