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

Copolymers of N-isopropylacrylamide (NIPAAM) and itaconic acid (IA) were pr epared via free radical polymerisation using potassium persulfate (K2S2O8) in distilled-deionised water at 50 degrees C in nitrogen atmosphere. The de pendence of the aggregation process on pH and ZA content and the copolymer composition were examined by means of UV-VIS, FTIR, and H-1 NMR spectroscop y, gel permeation chromatography (GPC), and viscosity measurements. Cloud p oints 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 NIPAA M content and decreasing pH. The differences in the phase transition temper atures were supposed to result from interactions between the isopropyl grou p and unionised carboxylic acid groups or electrostatic interactions betwee n the carboxylate groups, depending on the pH and hydrophilic constituent c ontent.