Observations on some copolymerisations involving N-isopropylacrylamide

Free radical copolymerisations of N-isopropylacrylamide (NIPA) with acrylic acid (AA), methacrylic acid (MAA) and 2-methyl-2-acrylamidopropane sulphon ic 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 necessar y to overcome rapid attainment of high conversion, crosslinking and irrepro ducibility for the systems containing AA and MAA as comonomers are discusse d. 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-Tu dos method. The 95% confidence ellipses were also computed. The results are : r(1) = 14.0 +/- 1.9 and r(2) = 0.07 +/- 0.09 fur NIPA(1)/AA(2), r(1), = 1 0.2 +/- 1.4 and r(2) = 0.01 +/- 0.03 for NIPA(1)/MAA(2) and r(1) = 2.4 +/- 0.8 and r(2) = 0.03 +/- 0.02 for NIPA(1)/AMPS(2). Hence none of these syste ms undergoes azeotropic copolymerisation. The extent of compositional heter ogeneity has been demonstrated by computed curves of instantaneous copolyme r composition at different stages of conversion. Examination of the rather limited literature on linear copolymerisations involving NIPA discloses pos sible flaws and uncertainties in some of the procedures employed. (C) 2000 Elsevier Science Ltd. All rights reserved.