Diacetylene oligomers

In this paper methods are described for preparing the 1,3,5-triethynylbenzene monomer and oligomers. Evidence is then presented to support the theory that these diacetylene oligomers tend to thermally cure by an aromatization reaction. 

For a long time it was unclear whether the triplet state (S = 1) of the dicarbenes ( DC) does exist, and if it does whether its energy is higher or lower than the energy Acsq of the dicar-bene quintet state ( DC). Miiller-Nawrath et al. [51] have shown theoretically and experimentally that the ESR transitions of the triplet states of carbenes ( C) and of dicarbenes ( DC), respectively, are mutually degenerated in diacetylene oligomers of diacetylene crystals if the... 

Poly(diacetylene) with a p-tosyloxymethyl side-group undergoes photooxidation when irradiated with visible light of wavelengths <520nm. Reaction products identified include hydroperoxy (OOH) groups, p-toluene-sulphonic acid and poly(diacetylene) oligomers. The photo-oxidation reaction proceeds by the ene mechanism [1732]. 

The optical spectra of these intermediates are the only significant source of information concerning the relationship of chain length and absorption energy for diacetylene oligomers. 

Figure 62 The unreacted (100), partially reacted (101), and completely reacted (102) diacetylene group-containing oligomers in the product from the reaction between 95 and Cp2Mo2(CO)6 (top). The X-ray diffraction spectrum (middle, left), TEM micrographs (middle, right), and conductivity plots (bottom) of the product from the reaction between 95 and Cp2Mo2(CO)6 after pyrolysis to 1000°C. (Adapted from ref. 130.)...

One approach to the determination of intrinsic properties, which has been utilized since the earliest interest in conjugated polymers, is to study the properties of related oligomers, as in the preceding paper ( ). It is, however, also possible to study model macromolecules, the polydiacetylene. The existence of solid state polymerization in diacetylene monomers has a long history (22, 23, 2 ), but it was not thoroughly studied until... 

In all experiments described in this work only extremely low concentrations of intermediates are considered. This is due to our interest which is primarily focussed on the most important initial steps of the polymerization reaction, which are characteristic of the overall polymerization reaction mechanism. Consequently only low final polymer conversion is exp>ected and, therefore, complications arising from the interaction between the intermediate oligomer states can be neglected. It will be shown that the low temperature conventional optical absorption and ESR spectroscopy are powerful spectroscopic methods which yield a wealth of information concerning structural and dynamical aspects of the intermediate states in the photopolymerization reaction of diacetylene crystals. Therefore, this contribution will center on the photochemical and photophysical primary and secondary processes of this... 

Huber and Schwoererdescribe e.s.r. experiments which show the existence of quintet states (S = 2) after u.v. irradiation at 4.5 K in perdeuteriated / -toluene-substituted diacetylene. Nine e.s.r. transitions per quintet were detected and were attributed to bicarbenes of short oligomers. E.s.r. has also been applied to the study of photochemical reactions of fluoro-substituted ketones with amines, tetraphenylborates, and organometals." ... 

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... 

The linear polymers were readily formed by both methods. A salient feature in both of the syntheses was the in situ production of a desired carboranylenesiloxane oligomer by the reaction of a lithiated carborane and a chlorinated siloxane species rather than the use of the commercial Dexsil monomer as in the case of Henderson et al. [25] and Houser et al. [29], This has afforded an enormous degree of variation in the compositions of diacetylene-containing carboranylenesiloxane polymers that is not available by the conventional route of Henderson et al. [25]. The effect of the reduction in the diacetylene concentration was apparent in the positions and the intensities of the DSC peak maxima of the crossUnking endotherms of 5a-c. Thus, it was observed that as the concentration of the diacetylene units in the polymer... 

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