Thermoassociative block copolymers of poly(N-isopropylacrylamide) and poly(propylene oxide)

At the present time, the thermoassociative block copolymers usually consist of a favorable soluble fragment and a temperature-responsive one. In this study, the ceric ion redox method and the atom transfer radical polymerization (ATRP) were applied to synthesize novel thermally sensitive ABA block copolymers of poly(N-isopropylacrylamide) (PNIPAAm,) and polypropylene glycol (PPO) by using PPO with molecular weight of 2000 g/mol as a precursor. Due to the different lower critical solution temperatures (LCST) of PNIPAAm and PPO, we were able to obtain thermoassociative block copolymers, which have PNIPAAm segments with higher transition temperature and PPO segments of lower transition temperature. As a result, our copolymers exhibited a two-stage phase transition in aqueous solution. This attractive behavior offers an opportunity to obtain nanoparticles or microaggregates. The aggregation of the block copolymers in aqueous solutions was monitored by using the dye technique. The size of the copolymer nanoaggregates was determined with the aid of the dynamic light scattering (DLS). The particles obtained from aqueous solution were visualized by means of scanning force microscopy (SFM) and scanning electron microscopy (SEM) methods.