Effect of polymer-metal complexation on the phase transition of thermoreversible copolymer gels

We have investigated the effect of transition metal complexation on the swe lling behavior in water of a new terpolymer gel made from N-tert-butylacryl amide (N-t-BAm) as the hydrophobic monomer, 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) as the hydrophilic monomer, and N,N'-methylenebisacryl amide (BisAm) as the cross-linker. At a critical balance of hydrophilicity and hydrophobicity, the terpolymer exhibited a sharp volume transition at 1 5 degrees C. A shift in the transition temperature of the terpolymer was ob served after complexation with trace metal ions. Electron paramagnetic reso nance spectroscopy (EPR) suggested a tetrahedral structure for the complexe s. We propose that the shift in volume transition temperature of the gel is due to subtle changes in the hydrophilic-hydrophobic balance resulting fro m the complexation of hydrophilic -SO3H groups of the gel with trace amount s of the metal ions.