Study of the temperature behavior of hydrodynamic dimensions of poly(N-vinylcaprolactam) polymer coils in light and heavy water

Variation of the hydrodynamic radius of poly(N-vinylcaprolactam) (PVCL) mac romolecules (M = 9.60 x 10(5)) in H2O and D2O with temperature was studied by dynamic light scattering and viscometry. In both solvents, the average d iameter of PVCL molecules decreases by more than 1.5 times with temperature increasing from 10 to 32 degreesC. At all temperatures studied, the PVCL m olecular dimensions in D2O are smaller than in H2O and, beginning with 30 d egrees C, decrease faster with increasing temperature. The phase separation temperature T-ps is 31.9 degreesC for PVCL in H2O and 31.3 degreesC for PV CL in D2O, which is clearly fixed by light scattering. At temperatures abov e T-ps, a sharp increase of sizes of structural units is observed by both m ethods, which indicates separation of the polymer to a microphase, the size of which increases in moving away from T-ps. Comparison of viscometric dim ensions of PVCL macromolecules and a series of synthetic polymers of simila r structure allows us to assume that T-ps corresponds to the theta temperat ure for PVCL in water.