The poly(N-isopropyl acrylamide-co-methoxy polyethyleneglycol monomethacrylate, NIPAM-co-MPEG) with different length of ethylene oxide (EO) were synthesized from their monomers, NIPAM and MPEGs. The numbers of repeating units of EO were 6, 10, 24, and 46. The chemical structure and mole ratio of the monomers was determined by Fourier transform infrared (FTIR), H-1-NMR, and C-13-NMR spectroscopy. The d-spacing increased with the number of EO and the values of the copolymers were in the range of 0.437-0.452 nm. The lower critical solution temperature of the poly(NIPAM-co-MPEG) shifted to higher temperature as the number of EO and the amount of MPEG increased. The change of chemical shift for methoxy proton in MPEG exhibited a larger than those of the other protons of the poly(NIPAM-co10-2MPEG). Activation energy (E-a) for methoxy proton in MPEG showed a larger value than that of the methyl proton in NIPAM. These NMR results indicate the fact that more significant conformational transformations occur in the methoxy group through the phase separation than in the methyl group in NIPAM. (c) 2006 Wiley Periodicals, Inc.