Effect of solvent interactions on swelling and microstructure of amphiphilic polyurethane networks

Amphiphilic polyurethane (PU ionomer networks were synthesized by urethane acrylate anionomer (UAA) precursor chains. These networks were prepared wit h water, dioxane (DO), and dimethyl sulfoxide (DMSO, and exhibited very dif ferent swelling behaviors in water/DO (UAADG) and water/DMSO (UAASG) solven t mixtures, which was due to the different solvent interactions between wat er/DO and water/DMSO. The additional important factor influencing the swell ing behavior in water/aprotic solvent mixtures was the hydrophilicity of th e UAA networks, which was different than the water-UAA network. interaction . The microstructure of UAA networks prepared with the water/aprotic solven t mixtures was greatly influenced by the water-solvent interactions. Unlike the water/DO mixtures, which had a relatively weak water-DO interaction, t he strong water-DMSO interaction largely restricted the ability of DMSO to solvate the UAA chain, which resulted in an increase in the aggregation of the hydrophobic segment and the hydrophilic/hydrophobic microphase separati on. Thus, UAASG; and UAADG networks showed very different swelling behavior s in the same swelling medium because of the microstructural difference bet ween these gels, which was confirmed by dynamic mechanical measurements. (C ) 2000 John Wiley & Sons, Inc.