Hydrophobic and hydrophilic aggregation of tailor-made urethane acrylate anionomers in various solvents and their network structures

Tailor-made urethane acrylate anionomer (UAA) chains show higher viscosity and polyelectrolyte behavior in dimethyl sulfoxide (DMSO) than in water and toluene. Water is a nonsolvent for the hydrophobic soft segment but a good solvent for the hydrophilic hard segments, so hydrophobic segments are agg regated and form particles in the water phase, resulting in a smaller visco sity. Also, the fact that the viscosity of UAA chains is lowest in toluene can be interpreted as a result of ionic aggregation due to the nonpolarity of toluene. The structures of UAA networks dramatically change with the nat ure of the solvents used (i.e., the interaction between the UAA chains and the solvents used changes); this is confirmed by the results of tensile pro perty, morphology, and wide-angle X-ray scattering data. Ionic aggregation formed in UAA/tuluene (UATG networks) and hydrophobic aggregation formed in UAA/water (UAAG networks) are locked in by a chemical crosslinking reactio n and result in a greater modulus and X-ray scattering intensity. The great er elongation and swelling ratio in methylene chloride of UATG networks pre pared in a UAA/toluene solution indicates that toluene is a better solvent than DMSO for the hydrophobic segments of UAA chains. Also, the greater swe lling ratio in a pH 11 buffer solution and greater modulus of UAAG networks show that water is a better solvent than DMSO for hydrophilic ionic segmen ts. (C) 2000 John Wiley & Sons, Inc.