Abstract
The effect of temperature on aqueous solutions of poly(N-vinylcaprolactam) (PVCL) samples of molecular weights ranging from 21 000 to 1.5 × 106 g mol-1 was monitored by dynamic light scattering (DLS), high-sensitivity microcalorimetry (HS DSC), and pressure perturbation calorimetry (PPC) from 10 to 80 °C. The polymer was soluble in cold water and underwent phase separation at TCP ∼ 31−38 °C, depending on the molecular weight. The phase transition was endothermic, with an enthalpy change of 4.4 ± 0.4 kJ mol-1. Stable particles of average diameters 80 nm (high molecular weight PVCL) and ∼ 180 nm (low molecular weight PVCL) formed above the phase transition temperature. The coefficient of thermal expansion of PVCL in water (αpol), determined by PPC, underwent a sharp decrease at the temperature corresponding to the onset of phase transition, then it passed through a maximum, and decreased continuously with increasing temperature. The stability of the particles formed in PVCL solutions kept at temperatures ex...
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