Structural Study on the UCST-Type Phase Separation of Poly(<i>N</i>‑isopropylacrylamide) in Ionic Liquid

Upper critical solution temperature (UCST)-type phase separation behavior and its conformational change of well-defined poly­(<i>N</i>-isopropylacrylamide) (pNIPAm) in deuterated room-temperature ionic liquid (IL), 1-ethyl-3-methylimidazolium bis­(trifluoromethanesulfonyl)­amide (<i>d</i>₈-[C₂mIm⁺]­[TFSA^–]), were investigated by means of dynamic light scattering (DLS) and small-angle neutron scattering (SANS) measurements. From the temperature dependence of time-averaged scattering intensity obtained by DLS, it was found that the cloud points of pNIPAm/<i>d</i>₈-[C₂mIm⁺]­[TFSA^–] solutions increased with molecular weight (<i>M</i>_w) and concentration. In addition, it was found that there are two relaxation modes of pNIPAm in the IL solutions. From SANS measurements, the radius of gyration, <i>R</i>_g, and the Flory–Huggins interaction parameter, χ, were evaluated as a function of temperature during the phase separation