Analysis of polyacetylene

M. Baranska, H. Schulz, R. Baranski, T. Nothnagel and L.P. Christensen, In situ simultaneous analysis of polyacetylenes, carotenoids and polysaccharides in carrot roots, J. Agric. Food Chem., 53, 6565-6571 (2005). 

M. (2011) Nondestructive Raman analysis of polyacetylenes in Apiaceae vegetables. /. Agric. Food Chem., 59 (14), 7647-7653. 

The cis/trans isomerization of cw-polyacetylene, previously only disclosed from spectroscopic data, has recently been detected by cyclic voltammetry The analysis of the redox data reveals that the trans-form is thermodynamically more favorable in the charged than in neutral state. 

A chemical reaction occurs above 1.5 GPa The sample turns black, new peaks develop in the Raman spectrum, and the absorption edge moves below 11,000cm. The recovered material has an optical band gap of 1.39eV, smaller than the band gap of polyacetylene. From the analysis of the Raman spectrum, it is seen that the C=C stretching mode completely disappears in the reaction product, while the C=N stretching band is present but at a different frequency than in cyanocetylene. In addition, the Raman bands of polyacetylene are observed with their characteristic frequency dependence on the wavelength... 

In 1982, Soga et al. 256> showed that exposure of acetylene to AsFs at low temperatures leads to rapid polymerization (in our experience this reaction can be explosively violent). The product is a solid polymer which is heavily arsenic-doped and has a conductivity several orders of magnitude lower than a conventional sample of polyacetylene saturation-doped from the gas phase. Aldissi and Liepins 2S7) have adapted this reaction to the preparation of soluble polyacetylene by adopting AsF3 as the reaction solvent. They claim that polymerization of acetylene with AsF5 is very rapid, giving a polymer which is soluble in common solvents. However, elemental analysis shows that the polyacetylene formed contains about one As atom per 10 CH units and this is not removed on repeated reprecipitations. It seems likely that the As atoms form part of the chain backbone, conferring sufficient flexibility to allow dissolution. It is claimed that films of soluble polyacetylene can be doped but very little information has been published. 

In many laboratories that have access to a nuclear reactor, neutron activation is used for the chemical analysis of rocks, minerals, petroleum, biological tissues, alloys, etc., and the technique is well suited for the determination of the concentrations of trace elements in polymers. Neutron activation analysis was used by Given et al. (1) in their studies of water tree growth in polymeric insulation and by Wu and Chen (2) in their studies of dopant-polymer interactions in MoCl5-dcped polyacetylene films. In this work the principles of the method are described and the possibilities are illustrated by means of measurements carried out on polyethylene. 

Haink, H.J. Jungen, M. Excited states of the polyacetylenes. Analysis of the near ultraviolet spectra of diacetylene and triacetylene. Chem. Phys. Lett. 1979, 61, 319-322. 

A recent theoretical analysis of the temperature dependence of the magnetic response of neutral disorder-induced solitons [69], has revealed that these solitons may explain the low-temperature deviation from Curie behavior that is observed in experiments on Durham trani -polyacetylene [70]. A more stringent test of the theory would involve extending these experiments to even lower temperatures (down to 1 K or lower). 

The question of the unit cell continues to receive attention. Pressl el al. [46] also conclude that a decisive analysis is not yet possible, after considering the influence of temperature factors, which need to be precisely known. A coexistence of P2i/n and P2 /a phases is anyway a reasonable explanation for the observations. Nevertheless, Zhu et al. [62] perform an analysis of off-axis x-ray intensities (Akagi polyacetylene), and come to favour the P2Jn structure, with either small fractions of / 2,/a phase or random defects... 

In this chapter the second moment studies are mainly reviewed for the two typical conjugated polymers Shirakawa-type (S-PA) [20-22,27,30-32] and Naar-mann and Theophilou-type (NT-PA) polyacetylenes [24] and polyparaphenylene [23,28,29]. The characteristic of NT-PA is a high degree of chain orientation attained by mechanical stretching, [33] which provides additional information on tlie polymer chain arrangement how much misorientatioii of the chains is left behind and how much of the amorphous portion exists [34]. From an analysis of the second moment M2... 

The first work reported was done at the beginning of the eighties and dealt with polyacetylene. (CH)x has been characterised under different forms foam [32] iodine doped [33] AsFs doped [34] IrClg doped (which exhibits a giant dielectric constant) [35] encapsulated [36] cis and trans isomers [37] anisotropic [38]. The volution of the transport mechanism with doping level has been studied by measuring evolutions of Oj)c and (75.5 GHz with temperature [39]. An analysis based on the fibrillar structure of polyacetylene has been given. Recent works have been published, as in the case of n-doped polyacetylene [40]. 

Yang and Chien [35] observed that the reaction of Shirakawa polyacetylene with perchlorate counter-ions can be explosive and that the perchlorate doped samples were more stable to oxygen than is the undoped material which is further supported by the work of Pochan el al. [83], Haq and Farrington [32] and Druy et al. [29] on iodine and perchlorate-doped Shirakawa polyacetylene. Aldissi [84] prepared polyacetylene by dissolving monomer and then exposing to AsF below -84"C. Thermo-gravimetric analysis of... 

The Htickel Model of Polyacetylene Revisited Asymptotic Analysis of Peierls Instability... 

We carry out an analysis of the spectrum the Hiickel model of dimerized polyacetylene, both for cycUc and open chain boundary conditions, with special emphasis on the linear polyene with odd number of ir bonds. We also perform explicit perturbation expansion up to second order in the nuclear displacements. The asymptotic analysis of first- and second-order perturbation theory reveals that some behaviours assumed in the literature are not correct. 

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