Copolymer Films Swollen in Water: NMR Relaxation and PFG NMR Techniques in Studying Polymer-Water Interactions

Abstract

NMR relaxation and NMR diffusion techniques have been applied to investigate the films from the copolymers of methacrylic acid and butyl methacrylate after their swelling in water. 1H NMR spectra and spin-spin relaxation times have been analysed to estimate the contributions of water protons and the protons of polymer matrix. NMR diffusion study in the films swollen in water discovered a dependence of the echo-attenuation signal on the diffusion time. The data obtained showed a restricted diffusion of water trapped in film pores. The results have been analysed taking into account the known physical models of water diffusion in materials. Applying the Tanner’s approach to the data on water self-diffusion in the copolymer films, the pore size and permeability have been estimated. The increase of the water immersion time resulted in an additional water uptake and increasing molecular mobility of water.

Keywords: Apparent diffusion coefficient Dapp, Copolymer films, Correlation times, Fourier transform (FT), Free induction decay (FID), NMR spectra, Permeability, Pulsed Field Gradient (PFG), Restricted diffusion, Spin-lattice (longitudinal) relaxation time T1, Spin-spin (transverse) relaxation time T2, Stimulated echo (STE), Water.