Uncommon Solution Behavior of Poly(N-vinylimidazole). Angular Dependence of Scattered Light from Aggregates in Ethanol

Abstract

Static light scattering measurements from high molar mass poly(N-vinylimidazole) (PVI) in ethanol displayed strikingly different angular dependencies from the PVI samples below M w = 8 x 10 5 g/mol. The high molar mass particles were considered as aggregates. A classification of the aggregate structure became possible by comparison with different, well-understood models. The shapes of the curves were examined, on one hand, on the basis of one-component models, with heterogeneity in segment density, and on the other, on the assumption of a two-component system. The observed scattering curves show behavior similar to the soft-sphere model and in another aspect to star-branched macromolecules with stiff arms. Also, a two-component analysis of the scattering data was successful with a globular architecture for the aggregates and coil behavior for nonattached linear chains. The analysis gave evidence to clustering of segments. A large number of the linear mass density was found combined with a considerable chain stiffness. Indications were found that the fraction of free chains was overestimated. A significant part of the chains appeared to be attached to the aggregates. Sterical stabilization in the course of dissolution of the glassy material, combined with hydrogen bonding, are suggested as the reason for the incomplete dissolution.