Crystal Structures of Three Crystalline Forms of Poly(vinylidene fluoride)

Abstract

ABSTRACT:The crystal structures of three forms of poly(vinylidene fluoride) were studied by X-ray diffraction method. Although the structure of form I has been determined to be a fully extended planar zigzag by Lando, et al. [orthorhombic; a= 8.58 A, b=4.91 A, and c(fiber axis)=2.56 A; space group Cm2m(C;!)], an alternatelydeflected molecular structure was postulated in order to release the steric hindrance between the fluorine atoms along the chain. A satistically disordered packing of such deflected chains satisfies the observed fiber period and improves appreciably the structure factor agreement. Form II is monoclinic [pseudo-orthorhombic; a=4.96 A, b=9.64 A, c(fiber axis)=4.62 A, and /3=90°; space group P21/c(C~h)], and its cell contains two molecular chains. The molecular conformation is essentially the TGTG type (internal rotation angles, 179° and 45°), and the glide plane of the molecular chain coincides with the c glide plane of the lattice. It is suggested that form III is monoclinic [a= 8.66 A, b=4.93

Collective polarization effects inβ-polyvinylidene fluoride and its copolymers with tri- and tetrafluoroethylene

“…17. This result does not support the model of Hasegawa et al, 40 who suggest that in ␤-PVDF monomers in a chain are tilted by 7°with respect to each other due to the steric hindrance of the neighboring fluorine atoms. ͑The tilt angle is defined as 180°minus the dihedral angle.͒ However, our calculations show that ␤-PVDF does develop tilts when some units are changed into TrFE or TeFE.…”

On blends of poly(vinylidene fluoride) and poly(vinyl fluoride)

“…It is apparent that the pattern changes substantially because of the presence of the a-form of PVF 2 • In particular, the shoulder at 20 = 20° (d = 4.4 A) and the broad reflection at 20 = 26.5° (d = 3.35 A) are indicative of the presence of the a-form. 4 Hence, the -ystructure does not appear to be stabilized by the presence of the PVF homopolymer as previously suggested 1 • 2 but seems to be due merely to the solvent history of the samples employed in these and earlier investigations. Specifically, in this study the -y-structure is produced by crystallization from DMF.…”

Simulation of α- and β-PVDF melting mechanisms

“…The α-PVDF unit cell is monoclinic with a P21/C space group and dimensions a ≈ 4.96 Å, b ≈ 9.64 Å and c ≈ 4.62 Å as reported by Hasegawa et al [11] and Doll et al [33]. This unit cell contains two anti parallel chains with two monomer (-CH 2 F 2 -) units in each chain as shown in Figure 1A.…”

“…This unit cell contains two anti parallel chains with two monomer (-CH 2 F 2 -) units in each chain as shown in Figure 1A. The β-PVDF unit cell is orthorhombic with a Cm2m space group and cell dimensions a ≈ 8.47 Å, b ≈ 4.9 Å and c ≈ 2.56 Å [11,34]. This unit cell has two planar zigzag chains with one monomer unit in each chain (i.e., half the number of atoms as in the α-PVDF unit cell), and is shown in Figure 1B.…”

“…This has attracted the attention of researchers for many years and a large number of experimental and theoretical studies on PVDF, including its crystal phases, have been made [6][7][8][9][10][11]. PVDF forms at least four crystalline phases, including the α-and β-phases.…”