The phase diagrams of semitelechelic and telechelic hydrophobically modified poly(2-isopropyl-2-oxazolines) (HM-PiPrOx) in water were characterized in terms of an extensive set of parameters: the cloud point ( T cp ), obtained from turbidity measurements, the transition temperature ( T M ) and enthalpy (Δ H ), derived from high-sensitivity differential scanning calorimetry (HS-DSC), the coefficient of thermal volume expansion, α, measured by pressure perturbation calorimetry (PPC), together with assessment by X-ray diffraction of the extent of polymer crystallization from hot water. Data were recorded as a function of the molecular weight of the polymers (7000, 10 000, and 13 000 g mol −1 ), the end-group functionality (α- n -octadecyl-ω-hydroxyl- or α,ω-di- n -octadecyl-), the polymer concentration (0.1−10 g L −1 ), and the solvent (H 2 O or D 2 O). For all polymer solutions, the cloud point temperature was lower than the transition temperature, in agreement with previous studies of telechelic HM-poly(ethylene oxides) and HM-poly( N -isopropylacrylamides) aqueous solutions. In solutions of all telechelic HM-PiPrOx and of the semitelechelic HM-PiPrOx 7000 and 10 000 g mol −1, the onset of turbidity was accompanied by an endotherm attributed to a rigid-to-fluid phase transition of the hydrophobic core of the polymeric micelles formed in aqueous solutions kept below T cp . Semitelechelic HM-PiPrOx samples crystallized from water upon prolonged heating at 70 °C, whereas telechelic HM-PiPrOx samples remained amorphous under these conditions. The results are discussed in terms of the dipole−dipole interactions between adjacent PiPrOx chains in the micelle corona which restrict the motion of n -octadecyl chains in the micellar core and favor intermicellar interactions. Water molecules acting as hydrogen-bound cross-linker between polymer chains also contribute to intra- and intermicellar PiPrOx chain association.
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Obeid et al. (2009) studied this question.