Micellization and phase transition behavior of thermosensitive poly(N-isopropylacrylamide)–poly(ɛ-caprolactone)–poly(N-isopropylacrylamide) triblock copolymers

Thermosensitive triblock copolymers with two hydrophilic poly(N-isopropylacrylamide) blocks flanking a central hydrophobic poly(ɛ-caprolactone) block were synthesized by atom transfer radical polymerization. Core-shell micellization of the triblock copolymers was inferred from the 1H NMR spectra derived in two different solvent environments (CDCl3 and D2O). The micellar characteristics of these amphiphilic triblock copolymers were studied by pyrene fluorescence techniques, dynamic light scattering and transmission electron microscopy. The critical micelle concentrations of the triblock copolymers were in the range of 4–16 mg/L and the partition coefficients were in the range of 3.10 × 104 to 2.46 × 105. The mean diameters of the micelles, measured by light scattering, were between 90 and 120 nm. The temperature sensitivity of the triblock copolymers was demonstrated by the phase transition of a 250 mg/L aqueous polymer solution at the lower critical solution temperature (LCST). The enthalpy of the phase transition was determined by differential scanning calorimetry. PM3 quantum mechanical calculation method was used to understand the intermolecular interactions between the copolymer and the water molecules. A modular approach was used to simulate the phase transition observed at the LCST.