ORIENTATION OF CROSS-LINKED POLY(VINYLIDENE FLUORIDE) CRYSTALLIZED FROM ORIENTED AMORPHOUS MELTS

Radiation cross-linked samples of poly(vinylidene fluoride) (PVF2), obtained from the Raychem Corp., were heated to above their crystalline melting point, stretched, and isothermally recrystallized at 100-degrees-C. The crystalline and amorphous orientation functions were studied as a function of cross-link density and extension ratio by X-ray diffraction and birefringence. The crystalline phase orients with its c axis parallel to the deformation direction, and the amorphous phase orients perpendicular to this direction. The degree of orientation of both the crystalline and amorphous phases increases with cross-link density and with extension ratio. Intrinsic birefringence values for both the crystalline and amorphous phases of PVF2 are offered. The intrinsic birefringence of the amorphous phase, calculated from bond polarizabilities and birefringence measurements using rubber elasticity theory, is 0.098 +/- 0.017. The intrinsic birefringence of the alpha crystalline phase as calculated from bond polarizabilities using the differentited Lorentz-Lorenz equation is 0.145 +/- 0.002. Each sample is characterized in terms of its polymorphic form by wide-angle X-ray diffraction, its molecular weight using Flory-Rehner theory, and the degree of crystallinity from density measurements. In addition, a value of phi = 0.15 is offered for the polymer-solvent interaction parameter in N,N-dimethylacetamide. Finally, attempts at drawing a correlation between the amorphous orientation functions of molten PVF2 samples and the orientation functions of these same samples after crystallization indicate that the crystalline orientation functions indeed depend upon the amorphous orientation functions of the deformed molten network rather than upon the cross-link density or extension ratio of the samples taken separately.