Observations on some copolymerisations involving N-isopropylacrylamide

Abstract

Free radical copolymerisations of N-isopropylacrylamide (NIPA) with acrylic acid (AA), methacrylic acid (MAA) and 2-methyl-2-acrylamidopropane sulphonic acid (AMPS) have been conducted over a range of conversions in ethanol, ethanol and water respectively. It was necessary to devise special methods for isolating the copolymers, since the common device of precipitation into a non-solvent could not be adopted here. Experimental procedures necessary to overcome rapid attainment of high conversion, crosslinking and irreproducibility for the systems containing AA and MAA as comonomers are discussed. For all three systems compositions of linear copolymers were determined by conductometric titration vs. aq. NaOH. The monomer reactivity ratios (r) were calculated from the initial monomer feed composition, the fractional conversion and the copolymer composition, by means of the extended Kelen-Tüdős method. The 95% confidence ellipses were also computed. The results are: r1=14.0±1.9 and r2=0.07±0.09 for NIPA(1)/AA(2), r1=10.2±1.4 and r2=0.01±0.03 for NIPA(1)/MAA(2) and r1=2.4±0.8 and r2=0.03±0.02 for NIPA(1)/AMPS(2). Hence none of these systems undergoes azeotropic copolymerisation. The extent of compositional heterogeneity has been demonstrated by computed curves of instantaneous copolymer composition at different stages of conversion. Examination of the rather limited literature on linear copolymerisations involving NIPA discloses possible flaws and uncertainties in some of the procedures employed.