LCST transition of PNIPAM-b-PVCL in water: cooperative aggregation of two distinct thermally responsive segments

Abstract

The self-aggregation behavior of poly(N-isopropylacrylamide)-b-poly(N-vinylcaprolactam) (PNIPAM-b-PVCL) during the thermal-induced phase transition in water was explored by a combination of calorimetric, turbidity, dynamic light scattering (DLS) and FTIR measurements. Only one transition can be observed via all detecting methods, revealing the cooperative aggregation of the two distinct temperature-sensitive segments. What is more, the combination of strong hydrophobic interactions among the entire polymer chains and hydrogen bonds of CO…H–N within PNIPAM segments results in the sharp variations at the LCST and gradual variations above the LCST during the phase transition of PNIPAM-b-PVCL aqueous solution upon heating. Additional analysis by perturbation correlation moving window (PCMW) and two-dimensional correlation spectroscopy (2Dcos) indicates that the hydrophobic C–H groups have an earlier response than the relatively hydrophilic CO groups during the LCST transition.