Investigation of the thermal aggregation in aqueous poly(N-isopropylacrylamide-co-itaconic acid) solutions

Copolymers of N-isopropylacrylamide (NIPAAM) and itaconic acid (IA) were prepared via free radical polymerisation using potassium persulfate (K₂S₂O₈) in distilled-deionised water at 50 °C in nitrogen atmosphere. The dependence of the aggregation process on pH and IA content and the copolymer composition were examined by means of UV-VIS, FTIR, and ¹H NMR spectroscopy, gel permeation chromatography (GPC), and viscosity measurements. Cloud points of 0.5 wt.-% aqueous solutions of the copolymers and of PNIPAAM were measured in the range of pH 1-9 and found to decrease with increasing NIPAAM content and decreasing pH. The differences in the phase transition temperatures were supposed to result from interactions between the isopropyl group and unionised carboxylic acid groups or electrostatic interactions between the carboxylate groups, depending on the pH and hydrophilic constituent content.