Diacetylene single crystal polymers

In addition to studies of diacetylene single crystals, current research, activities are focused on studies of the second X and third x order nonlinear optical responses of disubstituted diacetylene polymer films as active optical guided wave structures. Diacetylene polymers possess X values comparable to germanium(j 7). In the first stage, three major questions are being addressed ... 

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. 

The reactive species, which are responsible for the covalent bonding between the diacetylene molecules and thus lead to the formation of single-crystal polymer chains, have been identified spectroscopically [16, 17]. In the case of the shorter oligomers (n < 6), they are radicals, in which the two non-bonded electrons are each localised on one of the final C atoms of the oligomer. In the case of the long oligomers (n > 7), they are triplet-state carbenes, i.e. at each end of the oligomer... 

Phase-matched second harmonic generation in single crystal polymers was first observed in 2-methyl-4-nitroaniline substituted diacetylene polymers. Subsequently, a number of other diacetylene structures... 

Macro Crystals.—Nearly defect-free crystals of polymers have been produced by direct polymerization of monomer at gas-solid or liquid-solid interface. Poly-(diacetylene) single crystals have been produced from irradiation of the crystalline monomer and involves the instantaneous polymerization and crystallization of... 

MICROSTRUCTURES AND POLYMER CHAIN LENGTH IN DIACETYLENE SINGLE CRYSTALS... 

Figure 9.6 Absorption spectra of a thin TS diacetylene single crystal for light polarized parallel and perpendicular to the polymer axis b (T = 300 K). Monomer (M) and polymer (P) absorption.

The first reported and one of the best examples of the use of Raman spectroscopy to follow drformation in polymers is the case of substituted polydiacetylene single crystals [8-12]. The macroscopic polymer crystals are produced by the solid-state polymerization of substituted diacetylene single crystal monomers. The reaction is a topochemical solid-state polymerization [13], and the oystals produced have a high degree of perfection [14]. 

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. 

Colourless diacetylene monomer crystals can be polymerized under heat, ultraviolet. X-ray or y-ray irradiation to form single-crystal, highly coloured polyacetylenes. The solid state reaction transforms the entire monomer crystal to polymer crystal without phase separation the polymer forms a solid solution with the monomer over the entire... 

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... 

Fully conjugated and fully chain-aligned polymer single crystals with planar polymer backbone are obtained, which may have the alternative acetylene (ynene) or butatriene structures of Eq. (1). From our experiment we know that the acetylene structure is dominant in the polymer molecules. Up to now the best investigated diacetylene crystals are the TS-6 monomer crystals and the corresponding polymer crystals (poly TS-6). The substituents R and the notation of further diacetylene crystals discussed below are listed in Table 1. 

Some important aspects of topochemical polymerizations can be understood by inspection of Eq. (1), All reactivity comes about by very specific rotations of the monomers and by 1,4-addition of adjacent units and an extended, fully conjugated polymer chain is formed. The unique feature of the topochemical polymerization of diacetylenes is the fact that in many cases the reaction can be carried out as a single phase process. This leads to macroscopic, defect-free polymer single crystals which cannot be obtained, in principle, by crystallization of ready-made polymers by conventional methods. Thus, polydiacetylenes are ideal models for the investigation of the behaviour of macromolecules in their perfect three dimensional crystal lattice. 

A single crystal of monomer becomes a nearly defect-free single crystal of the polymer . The two most commonly used monomers are the phenylurethane and tosylate derivatives of 2,4-hexadiyne-l,6-diol, 233a and 233b, but the reaction has been accomplished with a variety of symmetrical and unsymmetrical diacetylene derivatives . 

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