Cocrystallization of poly(vinylidene fluoride) and vinylidene fluoride-tetrafluoroethylene copolymers: 1. Effect of chain structure and crystallization conditions

Abstract

Poly(vinylidene fluoride) and vinylidene fluoride-tetrafluoroethylene copolymers cocrystallize depending on the structures present in each. In the α-phase, the maximum difference in the defect concentration of the two polymers (Δ defect) equals 12.3% during isothermal crystallization, and is equal to 10.5% when the system is quenched. In the β-phase, it is 11.8% for isothermal crystallization, and ˜5.5% when quenched. Apart from isomorphic cocrystallization between components of the same polymorph, cocrystal formation between the α- and β-polymorphs was also observed. The resulting cocrystal adopts the structure of a particular polymorph, according to the results obtained from potential energy calculations. The interplanar spacings (d_hkl) of the α-phase of PVF₂ do not change with the H-H defect concentration, but for the β-phase d₂₀₀ increases with the defect concentration. The reason for this difference in behaviour has been attributed to the more compact nature of the β-polymorph unit cell, when compared to that of the α-polymorph. The limiting value of the Δ defect for cocrystallization in the α-phase has been attributed to the larger difference in the intramolecular potential energy, whereas that of the β-phase has been attributed to the compact nature of the unit cell.