Lower Critical Solution Temperature Determination of Smart, Thermosensitive N-Isopropylacrylamide-alt-2-Hydroxyethyl Methacrylate Copolymers: Kinetics and Physical Properties

The lower critical solution temperatures (LCSTs) were verified and determined for different molar feed ratios of N-isopropylacrylamide (NIPAAm) and 2-hydroxyethyl methacrylate (HEMA) monomers with ultraviolet spectroscopy and differential scanning calorimetry techniques. Increases in the NIPAAm monomer content played a crucial role in the LCST, which increased up to 36.7 degrees C at 50 mol %. However, a further increase in the NIPAAm monomer content steadily reduced the LCST, which decreased to 33 degrees C at 100 mol % NIPAAm [i.e., pure poly(N-isopropylacrylamide)]. The rate of copolymerization, assessed by the conventional conversion (%)-time method, and the apparent activation energies were determined. The reactivity ratios of the monomers, determined by the Kelen-Tudos and Fineman-Ross techniques, together with the results of an equation, showed that the polymer which formed was an alternating copolymer. The Q-e values for the NIPAAm monomer were determined. The equation showed the linear Arrhenius behavior of ln(r(1)-r(2)) versus the reciprocal of the temperature (where r(1) and r(2) are the reactivity ratios of NIPAAm and HEMA, respectively): the activation energy difference [i.e., (E-12 + E-21) - (E-11 + E-22), where E-12, E-21, E-11, and E-22 are various activation energies] was found to be -109 kJ/mol. The copolymers were characterized with H-1-NMR, C-13-NMR, Fourier transform infrared, ultraviolet-visible, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy techniques. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 2815-2825, 2008