The free-radical copolymerization of N-isopropylacrylamide and 2-acrylamido-2-methyl-1-propanesulphonic acid at varying comonomer mole ratios was studied at 70degreesC. The extent of conversion was determined as a function of time and comonomer mixture composition, and copolymer compositions were determined using elemental analysis and C-13 NMR spectroscopy. Monomer reactivity ratios were evaluated for low conversions using Kelen-Tudos and Fineman-Ross methods. The copolymers were characterized using C-13 and H-1 NMR spectra, FTIR spectroscopy, and differential scanning calorimetry. (C) 2003 Wiley Periodicals, Inc.