| Abstract
| - The effect of temperature on aqueous solutions of poly(2-isopropyl-2-oxazoline) (PIPOZ)samples of molecular weights ranging from 1900 to 5700 g mol-1 was monitored by turbidimetry, high-sensitivity microcalorimetry (HS DSC), and pressure perturbation calorimetry (PPC) from 10 to 80 °C.The polymers were soluble in cold water and underwent phase separation at TCP ∼ 45−63 °C, dependingon their molecular weight. The phase transition was endothermic, with an enthalpy change ranging from0.36 ± 0.01 to 1.16 ± 0.01 kcal mol-1. The coefficient of thermal expansion of PIPOZ in water (αpol),determined by PPC, underwent a sharp increase at the temperature corresponding to the onset of phasetransition, reaching a maximum value at T ∼ TCP. Microcalorimetric measurements were carried outwith solutions of PIPOZ samples in D2O and in aqueous NaCl solutions. The thermodynamic andvolumetric changes associated with the phase transition of aqueous PIPOZ solutions are compared tothose of aqueous solutions of two related polymers, poly(vinylcaprolactam) and poly(N-isopropylacrylamide)(PNIPAM), a polymer structurally related to PIPOZ that undergoes a phase transition in water at∼31 °C.
|
