Designing new thermoreversible gels by molecular tailoring of hydrophilic-hydrophobic interactions

We have shown that the lattice fluid hydrogen bond ~LFHB! model can successfully quantify the first-order volume transition in hydrogels. The model predicts that a critical balance of hydrophilic and hydrophobic interactions is required for a gel to exhibit a discontinuous volume transition. In this work we will report the swelling behavior of a new thermoreversible copolymer hydrogel, which has been synthesized from two monomers, whose homopolymers do not show any volume transition in water in the observable range of temperatures. The discontinuous volume transition phenomenon in the copolymer gel was observed only at a critical balance of hydrophilic-hydrophobic interactions. The discontinuous nature of the volume transition is lost with a subtle change in the hydrophilic-hydrophobic balance. The copolymer gel was synthesized from 2-acrylamido 2-methyl propane sulfonic acid ~AMPS!, which is a hydrophilic monomer, and N-tertiary butylacrylamide ~N-t-BAm!, which is a hydrophobic monomer. The hydrophilic-hydrophobic balance in the gel was altered by either changing the composition of the co-monomers or by substituting the N-t-BAm with another hydrophobic monomer, N-isopropylacrylamide ~NIPAm!. © 2000 American Institute of Physics. @S0021-9606~00!50604-7#