In this study, wide‐line NMR and x‐ray diffraction have been used in conjunction to study the crystal structure of poly(vinylidene fluoride). Drawn poly(vinylidene fluoride) film was found to contain two crystal phases, the relative amounts of each depending on the draw temperature. Drawing at 50°C. yields a single phase, designated as phase I, while drawing at temperatures between 120 and 160°C. yields a mixture of phase I and a second phase (phase II). The fraction of phase II increases with increasing draw temperature, but this phase was never obtained without some phase I. A tentative orthorhombic unit cell is proposed for phase II. The structure of phase I has been determined from x‐ray data. The unit cell is orthorhombic, space group Cm2m, having lattice constants a = 8.47, b = 4.90, and c (chain axis) = 2.56 A. There are two polymer chains in this unit cell. The conformation of the polymer chains is planar zigzag. The details of this structure have been confirmed by experimentally determining at −196°C. the change in the NMR second moment with the angle between the magnetic field and the draw direction of phase I (drawn at 50°C.), and by comparing these results with a theoretical calculation of the second moments, based on the atomic positions obtained from the proposed structure.

Infrared spectra representative of crystalline regions of cast films of phase-III poly(vinylidene fluoride) (PVF2) have been obtained by absorbance subtraction techniques using a FT-IR instrument. The spectra contain more bands than previously reported and are not consistent with current models for the crystal structure. Several possible models and their relationship to the corresponding crystalline spectra of phase II and phase I are discussed.

SynopsisThe interaction of water with collagenous tissue was investigated using dynamic mechanical spectroscopy and cryogenic X-ray techniques. The loss spectrum was found to be very sensitive to water which is highly associated with the macromolecule. Two water-sensitive loss peaks were observed below OOC: the 02 or "water dispersion" a t 150'K and the dl a t 200°K which is attributed to motion of polar side chains. Changes in peak temperature and intensity were not continuous with water content, but exhibited regimes in behavior which were associated with two types of nonfreezable water, structural and bound water. In cryogenic X-ray experiments, specimens which contained some freezable water exhibited reflections identified with the cubic form of ice. These ice crystals underwent an irreversible transition to the more common hexagonal form when warmed above 200°K. On the basis of these experiments, a model for the hydration of native collagenous tissue was proposed. INTRODUCTIONThe relation between water and biological macromolecules is one of the most important phenomena of all life processes. Connective tissue, for example, depends upon the association with water for the unique and specific mechanical properties. Here water is an important component of both the collagen fibers and the polysaccharide gel matrix which comprises the highly organized composite structure. Despite the obvious importance, many aspects of the structural protein-water interaction in the condensed native state remain a mystery. This is largely due to the complex chemical composition of the protein molecule and the equally complex hierarchies of structural organization which exist in connective tissue. A spectrum of interactions may be expected which differ as regards the energy of interaction and the effect on physical properties.Traditionally the water associated with proteins is divided into three types: structural, bound, and free water. High resolution X-ray diffraction data of protein crystals provide a description of the spatial arrangement of water molecules located within the crystal. The structural water associated with the crystal can be described by a specific stoichiometry much as the hydrates of inorganic salts. The term bound water is frequently used to describe protein-water interactions both in aqueous solution and the hydrated condensed state. The best definition remains an operational one in which the bound water is considered as that having properties measurably different from those of bulk water measured by the same technique. This definition includes considerably more water than the structural water.Although the actual value might be expected to vary considerably, different experimental techniques frequently give surprisingly similar values. For collagen, the amount of bound water is generally on the order of 0.35 glg. In addition, most collagenous tissue contains additional water in varying amounts which has essentially the properties of bulk water.In investigating the nature of water-collagen interactions we hav...

The crystal structure of the y phase of poly(vinylidene fluoride) (PVF2) was determined by X-ray diffraction techniques. Oriented specimens of the y phase were obtained by high-temperature drawing of films of ultrahigh molecular weight PVF2 cast from dimethylacetamide solution. The unit cell of the y phase was found to be orthorhombic with dimensions a = 0.497, b = 0.966, and c = 0.918 nm. The chain conformation is approximately TTTGTTTG'. Individual chains with this conformation possess a net electrical dipole and pack such that the unit cell is polar. The chains pack in a statistical parallel-antiparallel manner, which can be modeled by a hypothetical four-chain unit cell belonging to space group C2cm.Four crystal forms of poly(vinylidene fluoride) are known. The a phase, or phase II, is the form produced

The crystal structure of phase II (a phase) of poly(vinylidene fluoride) was studied by reexamining the work of earlier investigators. The reflections of phase II can be indexed to an orthorhombic unit cell with lattice parameters a = 0.496 nm, b = 0.964 nm, and c (chain axis) = 0.462 nm. There are two chains in this unit cell. The two chains pack with the chain dipole moments antiparallel. Three different ways of packing the chains, with respect to chain sense, were studied: both chains up, one up and one down, and a statistical up-down packing. It was found that to within a 96% confidence level, the chains pack with a statistical up-down packing.

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Potential-energy calculations have been used to investigate the effects of head-to-head defects on the chain conformation and packing of poly(vinylidene fluoride). The calculations have demonstrated that such positional isomerism can contribute to the polymorphism exhibited by PVF2. We have shown that increased concentration of head-to-head defects or tetrafluoroethylene comonomer can cause the phase-I form to become the favored structure for poly(vinylidene fluoride). The calculations have also proven capable of reflecting some of the subtle changes arising from the insertion of such defects. Packing calculations have shown that isomorphous replacement significantly affects the way in which PVF2 chains pack into a crystalline array. The differences in the structures proposed by Tadokoro and by Doll and Lando for phase II of poly(vinylidene fluoride) have been attributed to the inclusion of head-to-head defects in the polymer chains. In general, the potential-energy functions have proven useful qualitatively, if not semiquantitatively, in investigating the relation between chains in a crystal. Finally, these calculations have shown that both conformation and packing must be considered in determining the minimum energy structure for a polymer, and that these factors cannot be treated independently.

The crystal structure of phase IV (polar α or δ phase) poly(vinylidene fluoride) was studied by x-ray diffraction. Oriented phase IV was obtained by orienting phase II (α phase) and then corona poling at approximately 2 MV/cm. The resulting material is a mixture of phases I, II, and IV. Infrared spectra indicate that phase IV has the same chain conformation (TGTG′) as phase II. The reflections of phase IV can be indexed to an orthorhombic unit cell with lattice constants similar to the phase II lattice constants, a=0.496 nm, b=0.964 nm, and c (chain axis)=0.462 nm. There are two chains in this unit cell. The two chains pack with the chain dipole moments parallel. Three different ways of packing the chains were investigated: both chains up, one up and one down, and a statistical up-down packing. It was found that to within a 97% confidence level, the chains pack with a statistical up-down packing.