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 °C with α,α′-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 Cdouble bond; length as m-dashO stretching of secondary amides) and for IA (1704 cm−1 for Cdouble bond; length as m-dashO stretching) units, respectively. Monomer reactivity ratios of IA (F1)–NIPAAm (F2) pair were estimated using the Finemann–Ross, the inverted Finemann–Ross, the Kelen–Tüdós and the extended Kelen–Tüdós graphical methods. The values ranged from 0.40 to 0.60 for r1 and from 1.20 to 1.90 for r2, depending on the conversion percentage, calculation methods of monomer reactivity ratios and determination methods of copolymer compositions. In all cases, r1r2 < 1 and r1 < r2 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.