STUDIES ON SWELLING BEHAVIOR OF POLY(ACRYLIC ACID-co-OCTADECYL METHACRYLATE) HYDROPHOBIC ASSOCIATION HYDROGELS WITH HIGH MECHANICAL PROPERTIES

The hydrophobic association hydrogels (HA gels) were synthesized through micellar copolymerization of acrylic acid (AA) and a small amount of octadecyl methacrylate (OMA) in solution containing sodium dodecyl sulphate (SDS). The associated micelles consisting of surfactants and hydrophobes acted as physical cross-linking points in the network structure of HA gels. The mechanical properties of HA gels were measured by one-way tensile experiments, and the results confirmed the high toughness of as-obtained hydrogels. The mechanical properties were associated with the effective network chain density and the effective cross-linking point contents. With increasing the content of hydrophilic or hydrophobic monomer in the HA gels, the strength of HA gels all increased while the elongation at break all decreased. Furthermore, the swelling behavior of HA gels in aqueous solutions at different pH values was also investigated. It was found that the HA gels possessed unusual swelling behavior. The swelling process could be divided into three stages:namely, the gel erosion stage, swelling equilibrium stage and gel disruption stage. At strong acidity, the swelling of gel was restrained, and the gel disruption stage did not appear. At strong alkaline condition, the swelling of gels was accelerated so that the swelling equilibrium stage was overpassed. Last, the salt effect restrained the swelling of HA gels, however, in SDS aqueous solutions, the SDS would drag the hydrophobically modified polymers into solution,then new association network was formed, and thus the solution was thickened.