Chain collapse and dynamics of inhomogeneities in aqueous solutions of poly( <i>N</i> -isopropylacrylamide) and its block copolymers with polyethylene glycol

Spin probe EPR spectroscopy was used to investigate the polymer chain collapse in aqueous solutions of poly(<i>N</i>-isopropylacrylamide) (PNIPA) and its block copolymers with polyethylene glycol (PEG). The research demonstrated that for polymers with relatively low molecular weight, the polymer end groups and presence of comonomers significantly broaden the temperature interval of chain collapse. Inhomogeneities formed during the collapse process possess local polarity close to that in chloroform. Dynamic exchange of the probe molecules between inhomogeneities and bulk solution is observed for all the polymers studied.