The rq]-M relations of some commonly used two-parameter excluded-volume theories have been considered in regard to estimating Ko, a measure of unperturbed dimensions of polymers. Limitations of these theories have been demonstrated using [q]-M data of two substituted acrylamide polymers, poly(N-phenyl acrylamide) (PNPA) and poly(N-(p-methyl)phenyl acrylamide) (PNPMPA), which range in their v values from flexible to semi-rigid chain character. The analysis shows that the theories fail to accommodate any such set of [q]-M data that leads to v values larger than its prescribed limit in the corresponding theory. For the Flory-Fox-Schaefgen and Domb-Barrett theories V~ax came out to be 0.80; and for the Kurata- Stockmayer-Roig, Burchard-Stockmayer-Fixman and Inagaki-Ptitsyn theories it extended to unity. As a consequence of the failure of these theories, two more equations due to first-order perturbation and Bueche-James theories were invoked with a view to extending the scope of this analysis. The upper limit ofv was thus extended to 1.25 and 2.00, respectively. These theories were found to be of general applicability. The values of K o estimated by appropriate methods were 4.65 ? 10-* and 8.5 x 10 4dlmoll/2g 3,,2 for PNPA and PNPMPA, respectively.
Посилання на статтю:
Limitations of graphical procedures based on excluded-volume theories for the determination of Ko / S. Shashikant* and C. K. Patel // Polymer. – 1992. – Vol 33. – P. 4569-4574.