Infinite dilution viscoelastic properties of poly(γ‐benzyl‐L‐glutamate) in m‐cresol

The real and imaginary parts of complex viscosity, η′ and η″, are measured for dilute solutions of poly(γ‐benzyl‐ L ‐glutamate) in m‐cresol, a helicogenic solvent. The frequency range is 2.2–525 kHz; the concentration range 0.2–5 g/dl; the temperature 30°C, and the molecular weights M r are 6.4 × 10 4 –17 × 10 4 . The dispersion curve of extrapolated intrinsic dynamic viscosity [η′] of samples with M r > 10 5 is interpreted in terms of three mechanisms appearing from low to high frequencies: end‐over‐end rotation, flexural deformation, and side‐chain motion. For a sample with M r < 10 5 , the flexural relaxation disappears and a plateau of [η′] is distinctly observed between rotational and side‐chain relaxations. Rotational relaxation times of all the samples obey the Kirkwood–Auer theory. The strong concentration dependence of rotational relaxation time is explained by collisions of molecules rather than association. Flexural relaxation times calculated from a theory by assuming the persistence length as 1200 Å are consistent with observed dispersion curves of [η′].