Structure Determination of Novel Polydiacetylene Materials.
The major objective of this work has been to synthesize and characterize some novel diacetylene polymers. Monomers of the general type HC(TBOND)C-(CH(,2))(,n)-C(TBOND)CH were oxidatively coupled (Glaser coupling) to synthesize polymers of the form ( (CH(,2))(,n)-C(TBOND)C-C(TBOND)C )(,x). These polymers (n = 5, 6, 8), termed macromonomers, were subsequently exposed to CO('60)-(gamma) radiation to effect the diacetylene polymerization. The resulting materials, called crosspolymerized macromonomers, were composed of regular two-dimensional networks of polydiacetylene and hydrocarbon chains. Crystal structures of macromonomers before and after crosspolymerization were determined essentially by electron diffraction analysis, with supporting information from x-ray fiber diffraction. A detailed investigation of the crosspolymerization reaction was made by C-13 NMR in solid state. A very special type of diacetylene monomer was synthesized by dimerizing 1,11-dodecadiyne through a controlled oxidative coupling. Preliminary characterization of these dimers was accomplished by using GPC, DSC and electron diffraction. Macroscopic single crystals of polymerized dimer were obtained by radiation ((gamma)-radiation) induced polymerization and simultaneous crystallization from solution. X -ray diffraction analysis was employed for the crystal structure determination of this material. The structure was found to be composed of sheets of alternating polydiacetylene and polyacetylene chains. The nearest neighbor distance between a polydiacetylene and a polyacetylene chain was approximately 4(ANGSTROM). The electrical conductivity of this undoped material was measured and found to be reasonably high ((TURN)10('-2) (OMEGA)('-1)cm('-1)). A (pi)-electron band structure calculation indicated that such high conductivity resulted because of significant interchain interaction within the unit cell. A detailed investigation of the consequences of anharmonic interaction on diffraction intensities has been made. Anharmonicity in certain cases may lead to unexpected nonsystematic extinctions in the diffraction pattern. Anisotropy in anharmonicity may also cause unusual variations in the intensity distribution in some specific zones of reciprocal space. Crystal structure determination in such cases becomes impossible unless appropriate corrections are applied to the observed data. A general procedure for application of the necessary corrections had been outlined, along with some examples. A unified interpretation of various line broadenings (paracrystallinic, lattice strain, etc.) has been given in terms of higher order vibrations within a crystal. The explicit temperature dependence of the line widths, as derived from this treatment, was found to be in good accord with experimental results.
- Pub Date:
- Physics: Condensed Matter