Polymer, Vol.132, 164-173, 2017
Structure-property relations for temperature-responsive gels
A model is developed for equilibrium unconstrained swelling of thermo-responsive gels that takes into account formation of hydrophobic aggregates above the volume phase transition temperature (VPTT). The solid phase of a gel is treated as a polymer network with two types of junctions: covalent bonds that are formed under cross-linking polymerization of a pre-gel solution, and physical junctions that are developed due to aggregation of hydrophobic segments above VPTT. Adjustable parameters are found by fitting experimental data on poly(N-isopropylacrylamide) gels with various molar fractions of monomers and cross-linker and various routes of cross-linking (chemical reaction versus irradiation), furnished with sacrificial chains in pre-gel solutions, and synthesized under phase separation condition in mixed solvents. The ability of the model to describe equilibrium swelling diagrams is confirmed by numerical simulation. (C) 2017 Elsevier Ltd. All rights reserved.