Water vapour sorption behaviour of copolymers of N,N-diethylaminoethyl methacrylate and methyl methacrylate

Copolymers of N,N-diethylaminoethyl methacrylate (DEA) and methyl methacrylate (MMA) were synthesized in ethanolic solution and characterized in terms of reactivity ratios, densities and water vapour sorption. For the reaction conditions studied the copolymerization is essentially random. Polymer densities, determined by centrifugation in a density gradient, range from 1.10 for pDEA to 1.13 for p(DEA/MMA) 52/48 mol%. Flory-Huggins χ parameters were determined by isopiestic water vapour sorption, and were found to depend on both the comonomer ratio and the water content. An exceptionally strong dependence of χ on water content (or equivalently, polymer volume fraction) suggests that Flory-Huggins theory is not the proper theory to apply, especially for the polymers with the highest MMA content. Analysis of the data in terms of the Zimm-Lundberg cluster theory reveals that as the polymer becomes more hydrophobic and glassy with increased MMA, the sorption becomes more nonuniform in the polymer.