Polymer-solvent interactions during phase transition in poly(vinyl methyl eiher)/D2O solutions as studied by NMR methods

Abstract

The structural-dynamic changes and polymer-solvent interactions during temperature-induced phase transition in poly(vinyl methyl ether) (PVME)/D 2 O solutions in a broad range of concentrations (0.1-30 wt.-%) were studied by 'H NMR methods. In the whole concentration range the phase transition is manifested by line broadening (linewidth 350-500 Hz) of a major part of PVME units, evidently due to the formation of globular-like structures. Above the LCST transition, the fraction of phase-separated PVME segments is equal to 0.8 ± 0.1, independent of polymer concentration. While at low concentrations the transition is virtually discontinuous, at high concentrations the transition region is ∼ 3 K broad. Measurements of nonselective and selective 1 H spin-lattice relaxation times T 1 of solvent (HDO) molecules evidenced that at elevated temperatures, where most PVME forms globular structures, a part of solvent molecules is bound to PVME forming a complex; the lifetime of the bound water (HDO) molecules is ≤ 2 s.