Abstract
The storage and loss shear moduli, G′ and G″, have been measured for dilute solutions of three samples of poly(n-hexyl isocyanate) with molecular weights (M) from 0.99 to 10.0×105, by use of the Birnboim—Schrag multiple-lumped resonator. The frequency range was 100 to 6000 Hz, the concentration range 0.2 to 5×10−3 g/ml, and the temperatures 0°, 10°, 25°, and 37.8°C. Two solvents were used: Tetralin, and a Tetralin—Aroclor 1254 mixture in proportions close to 1:1 by weight. The molecular weight distributions were found to be narrow from dielectric dispersion measurements. The extrapolated intrinsic moduli, [G′] and [G″], were compared with predictions of various theories. For M=0.99×105 in both solvents, the low-frequency behavior agreed with the Kirkwood—Auer theory for rigid rods, with the relaxation time predicted from molecular dimensions. Over the entire reduced frequency range, the data could be described closely by a hybrid relaxation spectrum of one terminal relaxation time separated by a gap from a sequence of times spaced as in the Zimm theory (as previously found for poly(γ-benzyl-L-glutamate)). For M=3.3×105, in Tetralin, the data could be described by the Zimm theory with free draining (i.e., Rouse) and finite number of submolecules N=10 or by the Harris—Hearst theory with free draining and a persistence length of 400 Å. For M=3.3×105 in Tetralin—Aroclor, the molecule appeared more flexible, as shown by a fit to the Zimm theory with N=200 and the hydrodynamic interaction parameter h*=0.10. For M=10.0×105 in Tetralin, the data were described by the Harris—Hearst theory with slight hydrodynamic interaction and a persistence length of 63 Å. The appearence of increased flexibility in the presence of chlorinated hydrocarbon solvent and the decrease in persistence length with increasing molecular weight are consistent with other physical measurements, especially recent experiments of Yu and Rubingh, though the dynamic measurements appear to sample molecular motions which are weighted by shorter lengths than are equilibrium measurements.
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Nemoto, N., Schrag, J. & Ferry, J. Infinite-Dilution Viscoelastic Properties of Poly(n-hexyl isocyanate). Polym J 7, 195–201 (1975). https://doi.org/10.1295/polymj.7.195
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DOI: https://doi.org/10.1295/polymj.7.195