Volker Enkelmann

Macroscopic single crystals of polymers by solid-state polymerization: a study of the monomer to polymer phase transformation of 1.6- dicarbazolyl hexadiyne

The solid-state polymerization of 1,6-di(N-carbazolyl-2,4-hexadiyne (DCH) giving rise to macroscopic single crystals of the corresponding polymer is described with regard to structural aspects. The crystal structures of the monomer and polymer are discussed with respect to the observed solid-state reactivity. An autocatalytic acceleration in the conversion-time characteristics of the radiation-induced polymerization is attributed to a non-destructive phase transition as indicated by a sudden change in the lattice parameters and the elastic constants of the polymerizing crystal. The same phase transition occurs with destruction of the parent lattice during thermal polymerization. The Youngs modulus in the chain direction of radiation-polymerized crystals reaches the theoretical value expected for infinitely long polymer chains.

Topochemical Reactions in Langmuir-Blodgett Multilayers

Abstract The topochemical polymerization of diacetylenes and.the dimerization of cinnamic acid derivatives have been studied in Langmuir-Blodgett-multilayers. The resulting polymer films are of controlled thickness and morphology and exhibit excellent stability. Structure, morphology and phase changes occuring in monomer and polymer films have been investigated using spectroscopic methods, electron and x-ray diffraction. Possible applications of the polymer films are discussed.

Solved and Unsolved Problems in the Solid-State Polymerization of Diacetylenes

Abstract Knowledge of the conversion dependence of the molecular weight and molecular weight distribution is necessary in order to understand the mechanism of polymerizations. Until recently the determination of molecular weights has been an unsolved problem in the area of the solid-state polymerization of diacetylenes. In this paper a survey is given of experiments on the solution properties of two soluble polydiacetylenes. The polydiacetylene chain behaves in solution like a random coil of worm-like chains with typical persistence length of 15O A. The yellow-to-blue transition in P3BCMU was found to be connected to an aggregation process.

Radical Cation Salts of Arenes. Structure, Properties and Model Character for Conducting Polymers

Abstract Radical cation salts of arenes are obtained by anodic oxidation. They are a new family of organic conductors. Common structural principles are reviewed. Radical cation salts of oligomers of poly-p-phenylene have been prepared and characterized. The packing found in these model compounds can be used to construct models for conducting polymers.

Structure of Doped Polymers

Abstract Studies of the synthesis, molecular weight, structure and morphology of polyacetylene (PA) indicate that the average length of linar chain segments between structural defects like crosslinks and chain folds is of the order of 20 units. Several models for the crystal structure of trans PA are given. The influence of the morphology on the mechanism of charge tranport is discussed. The doping is found to be inhomogeneous and the macroscopic conductivity is controlled by the topology of interlamellar contracts.

Comparative Optical Investigations on the One-Dimensional Organic Metals (Perylene)2 (PF6) 1.1 × 0.8CH2Cl2, (Pyrene)1 2 (SbF6)7 and (Fluoranthene)2 (AsF6)0.2 (PF6)0.8

The reflectance spectra of different radical cation salts of the type (arene)2XF6 are reported (X=P, As, Sb). For light polarised perpendicular to the molecular stacks, the crystals exhibit the optical behaviour of an insulating molecular crystal, whereas for light polarised parallel to the stacks a pronounced plasma edge is observed. Compared to other organic metals the crystals show remarkably high values of the plasma energy. Because the concentration of the free carriers is obtained from the charge transfer between the radical cations and the inorganic counter ions, the effective mass of the free carriers may be calculated from the plasma frequency. The analysis of the reflectance data by a Lorentz-Drude model yields as well the values of the mean collition time, the electrical conductivity, and the bandwith.

Morphology of Pristine Poly (Acetylene) Obtained by Luttinger's Catalyst

Abstract Poly (acetylene) was jprepared as freestanding mechanically stable film using Luttingers catalyst. The cis isomer formed initially is stable during storage at room temperature over many days. Electron micrographs show a loose conglomerate of irregularly shaped platelets with a diamjeter of several ten nanometers and a thickness of less than 10 nm. Electron diffraction on the cis form shows the chain axes perpendicular to the lamella surface. Annealing conver ts the polymer into the trans isomer. Morphological changes are not observed. The chanins however tilt in the course of the phase transition associated with the isomerization. Films of the material obtained by Luttingers cataltyst show essentially the same electrical and mechanical behavior as the ones prepared by a Shirakwa-technique.

The Correlation of Proton-NMR, Fluorine-MMR and ESR-Experiments on Some (Fluoranthenyl)2 + XF 6 − Salts

Abstract In (fluoranthenyl)2 + XF 6 − salts (X = P, As, Sb) the temperature dependent proton relaxation rates are due to three processes, namely the interaction with (i) mobile paramagnetic species (above 160 K), with (ii) fluorine nuclei linked to the anions (between 160 and 40 K) and with (iii) fixed paramagnetic centers (below 40 K). Inserting As or Sb for P, the center atom of the anion, leaves the high temperature properties of the crystals unchanged but results in higher hindering potentials for the reorientational motion of the anions and in a shift of the phase transitions to lower temperatures.

Radical Cation Salts - A New Family of Organic Metals

Abstract Stable radical cations of arenes can be generated by anodic oxidation and can be separated at the anode in the presence of suitable anions as radical cation salts [ary12]†X in the form of shiny black crystals. Crystal structures and phase transitions in fluoranthenyl radical cation salts, a new family of organic conductors, are reported. The metal to semiconductor transition which is observed seems to be related to a distortion of the stacks of aromatic molecules perpendicular to the stacking direction.