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POLYMER INTERNATIONAL, cilt.56, sa.4, ss.547-556, 2007 (SCI-Expanded)
The polymerization and copolymerization of N-isopropylacrylamide (NIPAAm) and acrylamide (AAm) at different compositions, initiated by ceric ammonium nitrate alone, were studied in water at 60 degrees C. The dependence of the polymerization yield and molecular weight on the reaction temperature, nitrate ion concentration, presence of organic solvent and feed composition were examined by gravimetry, Fourier transform infrared (FTIR) spectroscopy and viscosity. The Viscotek system consists of three on-line detectors, namely right-angle fight scattering, refractometer and viscometer, which were used to determine the number-average molecular weight (M-n) and hydrodynamic radius (R-h) of the NIPAAm-rich copolymers. It was observed that both M-n and R-h values of the copolymers decreased with increasing AAm content in the feed. The reactivity ratios of NIPAAm (2) and AAm (1) were computed by the extended Kelen-Tudos method at high conversion, using FTIR analysis, and were found to be r(2) = 2.26 and r(1) = 0.34 for NIPAAm-rich copolymers, i.e. heterogeneous copolymers. From the determination of the lower critical solution temperature (LCST), i.e. phase transition of 2.0 wt% aqueous solutions of NIPAAm/AAm copolymers and NIPAAm homopolymer (PNIPAAm), using a UV-visible spectrometer, it was found that the hydrophilicity and LCSTs of the chains could be changed in a narrow temperature range by controlling the initial compositions. Turbidities (tau) obtained from the absorbance values at three different wavelengths (lambda; 400, 500 and 600 nm) were used to interpret the macromolecular phase transition from hydrophilic to hydrophobic structure. The effects of comonomer content and temperature on the coil-globule transition are discussed in terms of the slopes of the linear plots of log tau versus log lambda. (C) 2007 Society of Chemical Industry.