Transport and structural characteristics of crosslinked poly(ethylene oxide) rubbers

Three series of crosslinked poly(ethylene oxide) rubbers have been prepared by photopolymerization of prepolymer solutions containing: (1) poly(ethylene glycol) diacrylate (PEGDA) and H2O, (2) PEGDA and poly(ethylene glycol) methyl ether acrylate (PEGMEA), and (3) PEGDA and poly(ethylene glycol) acrylate (PEGA). All of these polymers have similar chemical composition (approximately 82 wt.% ethylene oxide), but the crosslink density and the content and chemistry of chain end groups are different. The effect of chain end groups and crosslink density on mass density, glass transition temperature (Tg), free volume, and H2, N2, CH4 and CO2 transport properties of the polymers was determined. The effect of temperature on gas permeability and solubility was also investigated. Many of the samples were amorphous. However, samples with high concentrations of PEGMEA could crystallize, and the formation of crystalline regions significantly decreased permeability. A generalized free volume model was used to interpret the effect of crosslink density and chain end groups on gas permeability and diffusivity, where free volume was characterized using two techniques: (1) density and group contribution theory, and (2) positron annihilation lifetime spectroscopy. Finally, the potential application of these materials for CO2/light gas separations was explored.