Temperature-Responsive Properties of Poly(acrylic acid-co-acrylamide) Hydrophobic Association Hydrogels with High Mechanical Strength

A novel type of hydrophobic association hydrogels (HA-gels) was prepared through micellar copolymerization of acrylic acid (AA), acrylamide (AAm) as basic monomers and a small amount of octylphenol polyoxyethylene ether acrylate with seven ethoxyl units (OP7-AC) as hydrophobic association monomer. The HA-gels exhibited desirable mechanical property and stably reversible phase transition between opaque and transparency. The influences of adding urea and varying AA:AAm molar ratio on the phase transition behavior were discussed, which indicated that the phase transition was introduced by forming or dissociating of hydrogen bonding between amide and carboxyl groups. The introduction of hydrophobic units (OP7-AC) to poly(acrylic acid-co-acrylamide) (P(AA-AAm)) copolymer would result in the adulterating and cross-linking effects on the transition temperature. The former sharply reduced the transition temperature while the later gradually raised it. The transition temperature became linearly dropping with the increasing sodium dodecyl sulfate (SDS) content in the HA-gels. Therefore, the phase transition temperature can be finely adjusted by means of changing AA:AAm ratio, concentration, OP7-AC and/or SDS dosages in the synthesis of HA-gels.