1H 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 transition in poly(vinyl methyl ether) (PVME)/D2O solutions and gels in a broad range of concentrations (c = 0.1-30 wt%) and crosslinking densities, respectively, were studied by H-1 NMR methods. Similar behaviour was found both for linear and crosslinked systems, indicating the formation of compact globular-like structures during the phase transition. The fraction of PVME segments in globular-like structures is similar to0.85 for solutions and similar to1.0 for swollen networks, independent of the polymer concentration or the crosslinking density. While for dilute PVME solutions the thermotropic transition as detected by NMR is virtually discontinuous, for semidilute and concentrated solutions, and for swollen networks, the transition sets in at lower temperatures and its width is several Kelvin broad. (C) 2001 Elsevier Science Ltd. All rights reserved.