Lower critical solution temperature determination of smart, thermosensitive N‐isopropylacrylamide‐alt‐2‐hydroxyethyl methacrylate copolymers: Kinetics and physical properties

Abstract

AbstractThe 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°C at 50 mol %. However, a further increase in the NIPAAm monomer content steadily reduced the LCST, which decreased to 33°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 copolymer 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(r1r2) versus the reciprocal of the temperature (where r1 and r2 are the reactivity ratios of NIPAAm and HEMA, respectively): the activation energy difference [i.e., (E12 + E21) − (E11 + E22), where E12, E21, E11, and E22 are various activation energies] was found to be −109 kJ/mol. The copolymers were characterized with 1H‐NMR, 13C‐NMR, Fourier transform infrared, ultraviolet–visible, thermogravimetric analysis, differential scanning calorimetry, X‐ray diffraction, and scanning electron microscopy techniques. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008