Single crystals solid-state polymerized

The conversion from monomer to polymer in the crystal proceeds via a diffusionless phase transition to form perfect polymer single crystals with the lattice parameters close to those of the original monomer crystals. During the course of the polymerization, the polymer chains and the monomer matrix form a homogeneous solid solution without any nucleation of the product phases, thus neither destruction nor fibrillation can be observed in the resultant polymer single crystals. Solid state polymerization of conjugated diynes is... 

The data obtained by Chance and Patel for the thenmd, JT-ray, and y-ray initiated single phase solid state polymerization of a diacetylene were numa-ically simulated by Baughman, who accounted for differences in auto catalysis shown by all three methods in terms of strain-related chain initiation and propagation caused by the change in dimensions of the crystal. An alternative ... 

The solid-state polymerization of diacetylenes is an example of a lattice-controlled solid-state reaction. Polydiacetylenes are synthesized via a 1,4-addition reaction of monomer crystals of the form R-C=C-CeC-R. The polymer backbone has a planar, fully conjugated structure. The electronic structure is essentially one dimensional with a lowest-energy optical transition of typically 16 000 cm-l. The polydiacetylenes are unique among organic polymers in that they may be obtained as large-dimension single crystals. 

Polydiacetylenes are obtained as single crystals by topochemical solid-state polymerization of the monomer single crystal. These compounds have received considerable attention because of their one-dimensionally -conjugated structure. Their unique --electron structures, and therefore superior third-order nonlinear optical properties, have been extensively investigated. 

A kinetic model for single-phase polymerizations— that is, reactions where because of the similarity of structure the polymer grows as a solid-state solution in the monomer crystal without phase separation—has been proposed by Baughman [294] to explain the experimental behavior observed in the temperature- or light-induced polymerization of substimted diacetylenes R—C=C—C=C—R. The basic feature of the model is that the rate constant for nucleation is assumed to depend on the fraction of converted monomer x(f) and is not constant like it is assumed in the Avrami model discussed above. The rate of the solid-state polymerization is given by... 

Poly diacetylenes. The polydiacetylenes (PDA s) are unique among highly conducting polymers discovered in the past years in that they can be obtained as highly perfect macroscopic single crystals.68 Upon solid-state polymerization of... 

Fibers produced in this manner have some shortcomings. For example, these fibers are of very short length, no more than 5-10 cm long, and are produced rather slowly. One should also add that the only single crystal fiber produced is based on solid state polymerization of certain substituted diacetylenes and the technique does not seem to be applicable to other systrans. 

Quite recently, Nakanishi et al. have reported an example of crystalline-state dimerization for which the product matrix is essentially of single-crystal character63. On the other hand, it may be assumed that any solid-state polymerization of diolefinic crystals, which results in an amorphous product, gives a pseudomorph. 

This contribution gives a review of recent spectroscopic investigations concerning the photophysical and photochemical primary and secondary processes of the solid state polymerization reaction in diacetylene single crystals. It will be shown, that diacetylenes are an unique model system for the study of the reaction mechanism of a solid state chemical reaction which is characterized by a variety of reaction intermediates. The polymerization reaction in these crystals is of special importance, due to the resulting polymer single crystals, which exhibit extraordinary anisotropic physical properties. 

Single crystals are commonly mounted on a four-circle diffractometer. This method may provide the quality of data necessary for structural refinements. However, polymer single crystals of usable sizes have been obtained only through solid-state polymerization of monomer crystals, such as in the case of poly-diacetylcnes. Oligomers and model compounds, however, have been obtained in single-crystal fonn in several cases, either from solution or from the vapour phase. 

Organic compounds with delocalized jr-electron systems, e,g., jr-conjugated polymers, are considered to be candidates for third-order nonlinear optical materials. Among them, polydiacetylenes (PDAs) are an important class of conjugated polymers that has attracted investigators from many different fields (7,2). PDAs, which can be obtained as single crystals by topochemical solid-state polymerization (5), have been extensively studied since 1976 (4). PDAs show large third-order nonlinear optical susceptibilities (5) and ultrafast optical... 

R. Nowak, J. Sworakowski, B. Kuchta, M. Bertault, M.Schott, R. Jakubas, and H. A. Kolodziej, Dielectric properties of single crystals of the substituted diacetylene pTS effect of the solid-state polymerization and phase transitions, Chem. Phvs. 104 467 (1986). 

Solid-state polymerization of a monomer, if it can be achieved topochemically, is an interesting approach to polymer single crystals. Several publications describing the polymerization of NVK in the crystalline state initiated by high-energy radiation [468-471],... 

In a solid state polymerization reaction monomer diacetylene crystals are transformed to polymer crystals in successive reaction steps. Nearly perfect polymer single crystals are obtained thermally (kT) or by UV- or X-ray irradiation (hv) of the monomer crystals [1-3]. Within the class of diacetylene molecules (R-C=C-C=C-R) which show this unusual chemical reaction, the TSHD (with side groups R = -CH2SO2-0-CH2) is the best known representative, which is characterized by a variety of reaction intermediates [4-19]. The unconventional reactivity and the unusual properties of the polymer crystal have attracted the interest of both, physicists and chemists. The general feature of the low temperature photopolymerization reaction is shown schematically in Fig. 1 by example of the diradical DR-intermediates. 

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