A study of the swelling of copolymers of NIPAM and DMA with water by NMR imaging

A range of copolymers of N-isopropylacrylamide and N,N-diniethylacrylamide (DMA) have been prepared and the properties of these materials in aqueous solution examined by nuclear magnetic resonance (NMR) imaging. All of the polymers apart from PDMA exhibit a lower critical solution temperature, with the temperature and width of the transition increasing with increasing DMA content. On exposure to water the polymers swell rapidly; the kinetics of mass uptake are seen to closely resemble those expected for Fickian kinetics, although the Frisch exponents are slightly larger than expected. NMR imaging however reveals that the diffusion of water into these polymers is highly anoinalous, With concentration profiles more typical of Case It diffusion. The deformation model of Thomas and Windle was used to analyze the water content profiles, and the resultant parameters used in the fits related to the structure of the two constituent monomer units