Diacetylene ultraviolet irradiation

Diacetylenes like [30o] after being laboriously prepared, are not polymerized either by heat or ultraviolet irradiation (Iwamura, 1990). Control of molecular packing in crystals is now needed. Introduction of the technology of liquid crystals or Langmuir-Blodgett membranes (Hupfer et al., 1981 Koch and Ringsdorf, 1981) may be of help. 

Convincing evidence for phase separation was obtained from the photopolymerization behavior of 6 in the mixed 6/DSPE monolayer films. Photopolymerization of diacetylenes is a topotactic process which requires the proper alignment of the 1,3-diyne moieties [35]. Thus diacetylenes typically polymerize rapidly in the solid state but not in solution. Polymerization is triggered by ultraviolet irradiation and proceeds via a 1,4-addition mechanism yielding a conjugated ene-yne backbone (Fig. 5). The reaction can be followed by the growth of the visible absorption band of the polymer. 

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... 

Air, the cheapest oxidant, is used only rarely without irradiation and without catalysts. Examples of oxidations by air alone are the conversion of aldehydes into carboxylic acids (autoxidation) and the oxidation of acyl-oins to a-diketones. Usually, exposure to light, irradiation with ultraviolet light, or catalysts are needed. Under such circumstances, dehydrogenative coupling in benzylic positions takes place at very mild conditions [7]. In the presence of catalysts, terminal acetylenes are coupled to give diacetylenes [2], and anthracene is oxidized to anthraquinone [3]. Alcohols are converted into aldehydes or ketones with limited amounts of air [4, 5, 6, 7], Air oxidizes esters to keto esters [3], thiols to disulfides [9], and sulfoxides to sulfones [10. In the presence of mercuric bromide and under irradiation, methylene groups in allylic and benzylic positions are oxidized to carbonyls [11]. 

Leaver, J., A. Alonso, A.A. Durrani and D. Chapman. The Biosynthetic Incorporation of Diacetylenic Fatty Acids into the Biomembranes of Acholeplasma laidlawii A Cells and Polymerisation of the Biomembranes by Irradiation with Ultraviolet Light. Biochim. Biophys. Acta. 727 (1983) 327-335. 

Substituted diacetylenes (10) comprise a well-studied family of materials, particularly for their polymerization behaviour after deposition in the multilayer state. However, it is also possible to polymerize monomers on the subphase surface prior to deposition [26]. Polymerization has been carried out using ultraviolet (UV) irradiation (254 nm) of energy 50Wm at the subphase surface under a nitrogen ambient. Conversion to 90% polydiacetylene is usually achieved within... 

Such studies did, however, suggest that the initial step in the polymerization reaction is a diradical (26), see Figure 5, apparently contrary to the evidence of the existence of carbene radicals in thermally polymerizing crystals (27), This apparent conflict has been resolved by an extensive series of studies of the photo- and thermal polymerization of diacetylenes at low temperatures conducted at the Universities of Stuttgart and Bayreuth- A review of this worK is in the course of publication and references to the extensive literature will be found there (20 - 30)- The most thorough studies have been made of the monomer TS, similar but less detailed results have been obtained for a number of other diacetylene monomers (31). In most of the experiments monomer crystals at 4 K are irradiated with ultraviolet radiation and studied by optical, EPR and ENDOR spectroscopy. At 4 K broad band irradiation produces stable oligomeric intermediates since polymerization cannot proceed by thermal activation. 

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