CHAIN STIFFNESS AND EXCLUDED-VOLUME EFFECTS IN DILUTE POLYMER-SOLUTIONS - POLY(ISOPHTHALOYL-TRANS-2,5-DIMETHYLPIPERAZINE)

Small-angle X-ray scattering, light scattering, and viscosity measurements were made on 18 sharp fractions of poly(isophthaloyl-trans-2,5-dimethylpiperazine) (PIDP), a flexible polyamide, ranging in weight-average molecular weight Mw from 2.6 X 103 to 2.4 X 106, with N-methyl-2-pyrrolidone (NMP) at 25 °C as the solvent. Both gyration radius and intrinsic viscosity data showed PIDP in NMP to be essentially unperturbed below Mw ~ 104 and perturbed above it by volume effect. When modeled by Kratky and Porod's wormlike chain, the unperturbed PIDP chain was characterized by a persistence length of 1.2 nm and a molar mass per unit contour length of 310 nm-1. It was found that the combination of the Yamakawa-Stockmayer perturbation theory for the radius expansion factor of a wormlike chain and the Domb-Barrett equation for a flexible chain accurately describes the dimensional behavior of PIDP in NMP over the entire range of Mw studied. © 1990, American Chemical Society. All rights reserved.