Monomer reactivity ratios of N-isopropylacrylamide-itaconic acid copolymers at low and high conversions

Copolymers of N-isopropylacrylamide (NIPAAm) and itaconic acid (IA) having various compositions were synthesized using free radical solution polymerization in 1,4-dioxane at 50 degrees C with (alpha,alpha'-azobisisobutyronitrile (AIBN) as initiator. The structures of the copolymers were confirmed by Fourier transform infrared (FTIR) spectroscopic technique. The copolymer compositions were determined by conductometric and potentiometric methods from the inflection points in the acid-base titration curves and by FTIR spectroscopy through recorded analytical absorption bands for NIPAAm (1620 cm(-1) for C=O stretching of secondary amides) and for IA (1704 cm(-1) for C=O stretching) units, respectively. Monomer reactivity ratios of IA (F-1)-NIPAAm (F-2) pair were estimated using the Finemann-Ross, the inverted Finemann-Ross, the Kelen-Tudos and the extended Kelen-Tudos graphical methods. The values ranged from 0.40 to 0.60 for r(1) and from 1.20 to 1.90 for r(2), depending on the conversion percentage, calculation methods of monomer reactivity ratios and determination methods of copolymer compositions. In all cases, r(1)r(2) < 1 and r(1) < r(2) indicate the random distribution of the monomers in the final copolymers and the presence of higher amount of NIPAAm units in the copolymer than that in the feed, respectively. (C) 2009 Elsevier Ltd. All rights reserved.