H-1 NMR study of thermotropic phase transition of linear and crosslinked poly(vinyl methyl ether) in D2O

The changes in the dynamic structure during temperature-induced phase trans ition in poly(vinyl methyl ether) (PVME)/D2O solutions and gels in a broad range of concentrations (c = 0.1-30 wt%) and crosslinking densities, respec tively, were studied by H-1 NMR methods. Similar behaviour was found both f or linear and crosslinked systems, indicating the formation of compact glob ular-like structures during the phase transition. The fraction of PVME segm ents in globular-like structures is similar to0.85 for solutions and simila r to1.0 for swollen networks, independent of the polymer concentration or t he crosslinking density. While for dilute PVME solutions the thermotropic t ransition as detected by NMR is virtually discontinuous, for semidilute and concentrated solutions, and for swollen networks, the transition sets in a t lower temperatures and its width is several Kelvin broad. (C) 2001 Elsevi er Science Ltd. All rights reserved.