Molecular configuration and hydrodynamic behavior of poly‐N‐tert‐butylacrylamide in methanol

The results of a light‐scattering study of six samples of poly‐N‐tert‐butylacrylamide in methanol are presented. Some confirmatory results have been obtained with the use of an ultracentrifuge. The derivation of molecular parameters from Zimm plots and centrifugation data is briefly described. Methanol is found to be a good solvent for poly‐NTBA, in which it behaves as a stiff molecule expanded beyond random flight predictions. The effect of the stiffness on the Zimm plots and on the interpretation of the results is discussed. Values of the weight‐average and number‐average molecular weights (M̄w and M̄n), the z‐average and number‐average radii of gyration (pz2)1/2 and (pn2)1/2 and the corresponding end‐to‐end distances (rz2)1/2 and (pn2)1/2 are found. r2 = 161N̄, where N is the degree of polymerization and r̄ is measured in Angstroms. Values are also obtained for the length of the statistical element, the Kratky‐Porod persistence length, the coiling factor, the molecular expansion factor, the second osmotie virial coefficient, (A2), and the Flory constants Φ and Kv. Equations for the variation of (pn2)1/2 and of A2 with molecular weight are derived: they are (pn2)1/2 = 3.76 × 10−9 M̄n−0.515 and A2 = 0.082 M̄w−0.515, respectively. The value of Φ is considerably less than that normally predicted, and possible reasons for this are suggested. Empirical relations involving the excluded volume effect are mentioned.