Radical copolymerization of N-isopropylacrylamide with anhydrides of maleic and citraconic acids

Abstract

Radical-initiated copolymerization of N-isopropylacrylamide (NIPA) with maleic (MA) and citraconic (CA) anhydrides was carried out in the presence of 2,2 ′-azobisisobutyronitrile (AIBN) as an initiator in 1,4-dioxane at 65 °C under nitrogen atmosphere. Structure and monomer unit compositon of the copolymers obtained from a wide range of monomer feed were determined by elemental analysis (content of N for NIPA units), Fourier transform infrared and 1H NMR spectroscopy. Monomer reactivity ratios for NIPA ( M 1)–MA ( M 2) and NIPA ( M 1)–CA ( M 2) pairs were determined by Kelen–Tüdõs (KT) and non-linear regression (NLR) methods using elemental and 1H NMR spectroscopy analyses data. They are r 1=0.45 and r 2=0.08 (KT, N analysis), r 1=0.44 and r 2=0.10 (KT, 1H NMR), r 1=0.45 and r 2=0.078 (NLR) for NIPA–MA monomer pair and r 1=0.52 and r 2=0.02, r 1=0.44 and r 2=0.04, r 1=0.51 and r 2=0.014 for NIPA–CA monomer pair, respectively. Observed tendency towards alternating copolymerization at ⩽50 mol% NIPA concentration in monomer feed and relatively high activity of NIPA growing radical was explained by H-bond formation between CO (anhydride) and NH (amide) fragments during chain growth reactions. Intrinsic viscosity, molecular weight and thermal behaviour of the synthesized copolymers were found to depend on the type of comonomer and the amount of NIPA units in the copolymers. These functional amphiphilic copolymers containing anion- and cation-active groups show both temperature and pH sensitivity and can be used for biological purposes as physiologically active macromolecular systems.