Polyacetylenes PA

One particularly successful method utilizes a soluble precursor system with polymerization being completed via the elimination of a small molecule to leave the fully conjugated polyacetylene chain. The route employs a fluorinated cyclic precursor molecule that is soluble in acetone and castable into continuous clear films (Fig. 1.5). 

Polyacetylene exists as both cis and trans forms. Typically, the cis conformation polymer is produced at low temperatures while the trans form is produced at higher temperatures. The cis form can be converted to the trans form by heating at temperatures in the region of 170-200 °C (Fig. 1.6). 

The properties of the polymer are largely determined by the conformation films of the cis material appear red in transmitted light, with smooth surfaces having a copper-coloured reflectance, while the trans material is blue in transmission and silver in reflection. 

Although the soluble precursor route to conducting PA has offered a number of advantages in terms of processability and stability, the fact remains that the doped polymer is still difficult to process and is unstable in air. 

The problems experienced with PA and its copolymers and blends has prompted extensive research into other potentially conductive polymer systems in which the constraints on applications are not so severe. One of the most popular methods of producing conjugated electronically conducting polymers is via the polymerization of resonance-stabilized aromatic molecules. Study of this type of polymer was prompted by the discovery that oxidation of pyrrole at a platinum electrode in the presence of a supporting electrolyte produced free-standing electrically conductive films. Many other aromatic systems have since been studied, and the major ones are now described. 

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Fig. 7. Cyclic voltammograms for the oxidation of polyacetylene (PA), polypyrrole (PPy) and polyqnaterthienyl (PQTh)...

Oxidative polymerization of trans-bis-deprotected 79 under Hay coupling conditions [54] yielded, after end-capping with phenylacetylene, the high-melting and readily soluble oligomers 80a-e with the poly (triacetylene) backbone [87,106] (Scheme 8). Poly(triacetylene)s [PTAs,-(C=C-CR=CR-C=C) -] are the third class of linearly conjugated polymers with a non-aromatic allcarbon backbone in the progression which starts with polyacetylene [PA,... 

Within the hydrocarbons containing olefinic double bonds, polyacetylene (PA) is the most thoroughly studied system. The great interest results from its extremely... 

Fig. 1 Building units of conducting polymers, (1) polyacetylene (PA) (2) polypyrrole (PPy), polythiophene (PTh), polyfurane (PFu) (3) polyphenylene (PP) (4) polyaniline (PANI) 5 polyindole (PIND) (6) polycarbazole (PCaz) (7) polyazulene (Paz) (8) polynaphthalene (PNa) (9) polyanthracene (PAnth) (10) polypyrene (PPyr) (11) polyfluorene (PFiu) (12) poly(isothionaphthalene) (PITN) (13) poly(dithienothiophene) (14) poly(thienopyrrole) (15) poly(dithienylbenzene) (1G) poly(3-alkylthiophene) (17) poly(phenylene vinylene) (18) poly(bipyrrole) (PBPy), poly(bithiophene) (PBT) (19) poly(phenylenesulfide) (20) 4-poly(thienothiophene) (21) poly(thienyl vinylene), poly(furane vinylene) (22) poly(ethylenedioxythiophene) (PEDOT).

The synthesis and characterization of polyacetylene (PA) provided new incentive for understanding 7r-electronic spectra, electron-phonon interactions and electronic correlations[l, 2, 14]. The electrical conductivity of chemically doped PA rivals that of metals. Families in Fig. 2 such as polydiacetylenes (PDAs), poly thiophenes (PTs), cr-conjugated polysilane (PSs) and polyparaphenylene vinylene (PPVs), among... 

Fig. 13. Progression of linearly re-conjugated all-carbon backbones from trans-polyacetylene (PA) through trans-poly(diacetylene) (PDA), trans-poly(triacetylene) (PTA), to carbyne.

Nechtschein et al.106/110 have carried out a detailed study of 1/Ti with frequency and temperature, both in undoped and doped polyacetylene (PA). Their data analysis shows that PA is quasi-ID system throughout the temperature range of study, except at very low temperatures. Their analysis further, showed that, the intra-chain diffusion follows power law behaviour, T n = 0.65 above 50 K, and T" n = 1.5 below 50 K. These arguments along with Sach s model111 may result in an empirical model for 1/T1 versus temperature data in a limited range of temperature. 

Similar linear curves were also found for some synthetic metals such as polyacetylene (PA) and poly (p-phenylene)(PPP) [144]. The slopes and two sets of... 

By carrying out experiments on the polymerization of acetylene by using a concentrated Ziegler-Natta catalyst solution, Shirakawa and Ikeda were the first to report on the preparation of partially crystalline polyacetylene (PA) films under well-defined conditions [2]. Some six years later, Shirakawa, McDiarmid, and Heeger and colleagues [3] presented unequivocal evidence that, after doping with iodine vapor, the room-temperature electronic conductivity of PA film was... 

Polyacetylene (PA), the simplest linear conjugated polymer, has been actively studied for two main reasons. First, the discovery of the direct synthesis method of PA films on the surface of a Ziegler-Natta catalyst solution [1]. Second, the discovery of a large increase in electronic conductivity, due to a synthetic metal by doping with small quantities of electron-attracting species such as iodine, AsFs, etc., or with an electron donor such as sodium. However, because of its high reactivity and poor solubility, it is difficult to obtain the experimental structural data of PA. 

The mechanical and electrical properties of polyacetylene (PA) were modified by blending it with polybutadiene (PB). Further enhancement of the electrical conductivity of the blends was obtained by stretch elongation of the blends prior to doping. 

Radical-Cation Salts as Models for Conducting Polymers. Polymers that have an extended Tr-electron system in their backbones, for example, polyacetylene (PA) and poly(p-phenylene) (PPP), can be transformed by oxidation or reduction in the solid state (doping) to derivatives that exhibit metallike conductivity (24, 25). These materials are usually insoluble and infusible and exhibit a very complicated morphology that cannot be changed by subsequent treatment. The lack of knowledge about the structure and state of order is the cause of the current controversy about the conduction mechanism in doped polymers. 

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