Ionization and order-disorder transition of hydrogels with ionizable hydrophobic side chain

pH dependence of the structural change of the amphiphilic copolymer gels co ntaining the crystallizable side chain with carboxylic end group, poly(16-a cryloylhexadecanoic acid (AHA)-co-acrylic acid (AA)), has been investigated . The poly(AHA-co-AA) gels could maintain the crystalline domain of AHA uni ts up to pH = 11 at ambient temperature, which abruptly transferred into di sordered state beyond this pH due to the dissociation of the carboxylic gro up of AHA. However, the addition of salt or divalent ion enabled to crystal lize the gel even at pH = 11.5 due to the effective shielding of the electr ostatic repulsion. The mechanism of order-disorder transition through chang es of pH and salt concentration was discussed in terms of association-disso ciation of AHA groups. (C) 2000 Elsevier Science B.V. All rights reserved.