Poly acetylene PA

PA has two isomers, trans and cis. Since the latter does not have a degenerate ground state, interest has focused on the preparation of high-quality samples of trans- A. A Ziegler-type catalytic surface has been used to produce films of PA from acetylene [97]. The ratio of cis to trans can be controlled with reaction conditions low temperatures favour cis 

The advent of the Durham route developed by teams at Durham University and BP Research introduced higher-quality material and an important concept in the preparation of conjugated polymers [98]. The Durham route involves the preparation of trans-FA via a soluble precursor polymer, which can be cast and the resultant films then stretch-aligned before thermal conversion (Fig. 4.17). The use of the precursor route allows processing and alignment to be achieved on what is otherwise an intractable material. Other methods that will be discussed later are the prerequisite to any real application of these materials. 

Study of the third-order nlo properties of PA was originally undertaken to investigate the precise nature of the band structure of the polymer, and was to compliment other work on photo-excitation. Measurement of the THG of trans-FA was first reported in 1982 [99, 100], and the frequency dependence of both cis and trans forms has since been measured [101]. Taking into account the lack of orientation of the chains in the sample, a value of around 10 °esu at 1.5 eV was obtained. This value increases dramatically below 1 eV, showing a peak at 0.91 eV, where there is a two-photon enhancement from a partially forbidden transition, and a maximum of 1.3 X 10 esu at 0.65 eV at the three-photon resonance. The magnitude of the THG for czs-PA is around four times lower than for trans. 

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Figure 8. Raman spectra for various polyconjugated systems in the spectral range of the bond alternation mode carbyne (CA), poly(acetylene) (PA), poly-(octylthiophene) (POT), poly(iso-thianaphtene) (PITN), highly oriented pyrolytic graphite (HOPG), and Ceo (BF).

Figure 10. Resonance cross-section for the bond alternation mode Raman line in poly(acetylene) (PA), potassium reduced carbyne (CA) and fuUerene (Ceo)- The cross-section is in arbitrary units. The full drawn lines are as calculated from the A-term in the Albrecht theory. The dashed line is a guide line for the eye.

Previously, Hogen-Esch reported the successful synthesis of block copolymers composed of poly(acetylene) (PA) segments (PS-b-PA), by the living anionic block copolymerization of styrene and phenyl vinyl sulfoxide, followed by thermal treatment [158]. In this way, poly(phenyl vinyl sulfoxide) was completely converted to a PA segment A similar block copolymer was obtained by the reaction of chain-end-amine-fimctionaHzed poly(4-methylphenyl vinyl sulfoxide) with chain-end-COOH-functionaHzed PS via ionic interaction, followed by thermal treatment [215]. 

Amount of deposited material - The difference in weight loss between coated and untreated silica corresponds to the weight of the plasma-polymerized film deposited on the surface. For the plasma-treated silicas, decomposition of the coating starts at 265°C for poly acetylene, 200°C for polypyrrole, and 225°C for poly thiophene, and is complete at 600°C. Between 265 and 600°C, PA-silica shows 6 wt% weight loss, and PPy- and PTh-silicas show 4.5 wt% and 5 wt% loss, respectively. 

In all the cases of poly acetylene, polythiophene, and polypyrrole coating, the amount of plasma-film deposition was different, caused by the difference in the structure of the three different monomers and their reactivity during the plasma process. PPy- and PTh-silica are more hydrophobic than PA-silica, probably due to the presence of different chemical moieties in the complex film structure deposited onto the silica surface. 

The liquid crystal polymerization method was modified to prepare a vertically aligned poly acetylene film [58]. As a result, a film with a very curious morphology was formed that was composed of two layers. The layer on the solvent side had a vertically oriented fibrillar structure, whereas the layer on the acetylene gas side had a randomly oriented one. The modified method is very promising for visualizing the polymer growth process and clearly demonstrates that PA chains grow in a liquid crystal solvent. 

Coconut shell charcoal (average pore diameter 2.0 nm, surface area 1700 m g average particle size 10 pm) 80 wt%, acetylene black conductor 10 wt%, and poly-tetrafluoroethylene binder 10 wt% were mixed, ground, and pressed at 6 MPa to form a disk composite 10 mm in diameter and 0.55 mm thick. A pair of these disk composite electrodes were dried at 300°C below 7.5 x 10 Pa for 3 hours. Afterward they were cooled in an argon atmosphere, and an electrolyte was immersed in them under reduced pressure. By sandwiching a nonwoven polypropylene separator with the two identical immersed electrodes, a 2032 coin cell was assembled with a stainless spacer, as depicted in Figure 17.6a. 

Poly(/7-phenylenevinylene) may be considered a regular copolymer of acetylene and benzene [128]. Electron structures of PA, poly(p-phenylene), and poly(p-phenylenevinylene) were studied by using UV photoelectron spectroscopy and quantum chemical calculations based on the valence effective Hamiltonian method. Excellent agreement between the theory and experiment allows a detailed description of the evolution of the electron structure in this polymer series. 

Among group 8 transition metal catalysts, iron-based Ziegler-type catalysts such as Fe(acac)3-Et3Al (1 3) have been well known from the early stage of the catalyst investigation. They are readily prepared in situ to polymerize sterically unhindered terminal acetylenes such as n-alkyl acetylenes, sec-alkyl acetylenes, and PAs. The poly(PA) formed has red color and cis-dsoidal structure, and is insoluble and crystalline. 

In addition to PA, related polymers with substituent groups, e,g, poly(phenyl acetylene), poly-(1,6-heptadiyne) and copolymers have been investigated. In general, the conductivity achieved on doping is less than that for PA. 

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