Consequences of Structural Differences in Ionomer Networks Prepared in Different Solvents

Very different structures and properties result from the preparation of polymer networks from the same weakly charged polyurethane acrylate anionomer (UAA) dissolved in two different solvents, water and dioxane, during cross-linking. The UAA polymer readily dissolves in organic solvents such as dioxane but forms dispersions with water. Networks prepared in water (UAAG networks) and then dried show much higher hydrophilicity (swelling in water of pH 11) than their counterparts (UADG networks), which are cross-linked in dioxane and then dried. The different thermodynamic equilibrium structures achieved in the two polymer/solvent mixtures are locked into different network structures by the cross-linking reaction.