Study of Self-Diffusion of Molecules in a Polymer Gel by Pulsed-Gradient Spin-Echo ¹H NMR. 2. Intermolecular Hydrogen-Bond Interaction between the Probe Polymer and Network Polymer in <i>N</i>,<i>N</i>-Dimethylacrylamide−Acrylic Acid Copolymer Gel Systems

Abstract

Dynamics and structure of swollen N,N-dimethylacrylamide (DMAA)−acrylic acid (AA) copolymer gels, poly(N,N-dimethylacrylamide) (PDMAA) gels, and poly(acrylic acid) (PAA) gels have been studied as a function of the degree of swelling (Q) under a state of equilibrium with deuterated water (D2O) as a solvent and poly(ethylene glycol) (PEG) as a probe polymer by NMR methods. The self-diffusion coefficient (D) and 1H spin−spin relaxation time (T2) of PEG in the gel have been determined by the pulsed-gradient spin-echo 1H NMR method and Carr−Purcell/Meiboom−Gill 1H NMR method, respectively. From these experimental results, it was found that the D and 1H T2 values of PEG in the PAA gel are much smaller than those in PDMAA gel. This shows that the “loose” complex between the PEG and PAA network in the gel is formed by intermolecular hydrogen-bond interactions. From the experimental results on (DMAA−AA) copolymer gels with varying mole fractions of AA (fAA), it was found that the D and 1H T2 values in the gels with fAA ≥ 0.9, which have long consecutive AA sequences in the network, become much smaller than those in the gels with fAA < 0.5. This shows that the complexation is greatly influenced by the length of the consecutive AA sequences.