| Popis: |
In contrast to type I poly(vinylidene fluoride) (PVDF), solutions of type II PVDF contain, even in good solvents, a fraction of microgel that cannot be fully eliminated for characterization by light scattering. Intrinsic viscosity and size exclusion chromatography reveal that the soluble fraction has a molecular mass in the same range as type I samples, which are fully soluble in the same solvents. The shear moduli in the molten state reveal that the microgel fraction does not contain a high enough molecular mass to explain microgel formation by phase separation. From an analysis of the 19 F nuclear magnetic resonance spectra of both suspension- and emulsion-polymerized PVDF samples, with first-order Markov statistics, microgel formation is attributed to differences in microstructure, involving sequences with two reversed additions in a row. |
