Polyacetylene polymerisation

The most commonly used form of polyacetylene is produced by the Shirakawa method, which involves the direct polymerisation of acetylene gas onto a substrate at... 

There are reports of polymerisation of pyrrole [161, 162] and aniline [163] onto polyacetylene, to give oxygen and water stability [161], although there is some evidence for the polyacetylene acting electrocatalytically, oxidizing the pyrrole with no concomitant polymerisation. 

Catalytic forms of copper, mercury and silver acetylides, supported on alumina, carbon or silica and used for polymerisation of alkanes, are relatively stable [3], In contact with acetylene, silver and mercury salts will also give explosive acetylides, the mercury derivatives being complex [4], Many of the metal acetylides react violently with oxidants. Impact sensitivities of the dry copper derivatives of acetylene, buten-3-yne and l,3-hexadien-5-yne were determined as 2.4, 2.4 and 4.0 kg m, respectively. The copper derivative of a polyacetylene mixture generated by low-temperature polymerisation of acetylene detonated under 1.2 kg m impact. Sensitivities were much lower for the moist compounds [5], Explosive copper and silver derivatives give non-explosive complexes with trimethyl-, tributyl- or triphenyl-phosphine [6], Formation of silver acetylide on silver-containing solders needs higher acetylene and ammonia concentrations than for formation of copper acetylide. Acetylides are always formed on brass and copper or on silver-containing solders in an atmosphere of acetylene derived from calcium carbide (and which contains traces of phosphine). Silver acetylide is a more efficient explosion initiator than copper acetylide [7],... 

Polyacetylene, (CH),(, is a simple, conjugated polymer which may have either a trans or a cis configuration (Fig. 9.1). Free-standing films of polyacetylene can be easily obtained by catalytic polymerisation of gaseous acetylene, the most common procedure being the Shirikawa... 

As regards the metathesis polymerisation of cyclic trienes, it has been carried out in an attempt to find alternative routes for preparing soluble and meltable precursors of polyacetylene [149, 150], Hence, several substituted or unsubstituted tricyclic or other polycyclic trienes were subjected to polymerisation in the presence of metathesis catalysts such as WCl6-SnMe4 [151-154] and the tungsten neopentylidene complex [Me(F3C)2CO]2W(=NAr)(=CHCMe3) [155]. A successful solution of the problem is outlined below [125,150] ... 

The policyclic triene monomer undergoes metathesis polymerisation exclusively by the cyclobutene double bond under mild conditions (in toluene solution at 20 °C) to give a soluble precursor polymer. This polyacetylene precursor can be purified and characterised prior to its conversion at elevated temperature, via thermally initiated symmetry-allowed elimination (retro Diels-Alder reaction), to polyacetylene (a heat treatment of the product also results in isomerisation of the initial cis form to a more stable turns form) [150],... 

An alternative approach to the preparation of polyacetylene is provided by the ring-opening polymerisation of 1,3,5,7-cyclooctatetraene in the presence of a metathesis catalyst, e.g. WCU—AlEt2Cl-epichlorohydrin (Cl4W[OCH(CH2Cl)2 —AlEt2Cl) [157-163] ... 

An interesting extension of cyclooctatetraene polymerisation is the polymerisation of trimethylsilyl-substituted cyclooctatetraene to give soluble polyacetylene substituted with one trimethylsilyl group every eight carbon atoms [162], Such materials have been used to construct solar cells [165],... 

Indicate cycloolefin monomers that will be polymerised by metathesis catalysts to polymers with a structure equivalent to polybutadiene, an alternating ethylene/ butadiene copolymer, an alternating butadiene / isoprene copolymer and polyacetylene. 

Acetylene was first polymerised to polyacetylene (polyvinylene) according to scheme (1) by Ziegler, who patented a process employing new catalysts prepared from transition metal salts and metal alkyls [1] ... 

Polyacetylene has promise as a polymeric electroconducting material [26-31]. The simplest way to obtain this polymer is by polymerisation of acetylene, although alternative methods involving the metathesis polymerisation of cyclic polyenes are also effective. 

The cis-trans content of polyacetylene formed with coordination catalysts depends on the polymerisation temperature the increasing trans content with increasing polymerisation temperature has been explained in terms of a thermally induced cis-trans isomerisation which occurs before crystallisation of the chain segment [10,76 78],... 

A high-molecular-weight, insoluble polymer is obtained when perfluoro-2-butyne is subjected to various initiators for free-radical polymerisation (Figure 7.87). The off-white colour of this material is remarkable for a polyacetylene [307, 308]. Indeed, it is largely ignored in discussions on polyacetylenes because, of course, the fact that it is not coloured also means that the system is not conjugated the trifluoromethyl groups keep the TT-systems out of plane relative to each other. 

Unfortunately, even for the simplest and most studied case, the polyacetylene film, there is not a homogeneous network [5]. The mixing of the amorphous and the crystalline part makes the average properties observed, much more difficult to interpret. Not only does the very complex structure of the conducting polymer films produce scattered data for the conductivity, but the spectroscopic data are often dependent on the packing and chain conformation. As a consequence, the electronic properties of conducting polymer films may vary from one sample to another. Therefore, a major difficulty arises in deciding whether or not the difference observed was as a result of the chosen chemical structure and polymerisation route or of the way the molecules were packed. 

The first conducting polymer to be synthesised was polyacetylene. When polymerised, acetylene (ethyne) forms a silvery flexible film of polyacetylene. Acetylene (ethyne) has a formula C2H2. The carbon atoms are linked by a triple bond, consisting of 1 sp-hybrid a bond and two n bonds (Scheme 13.2). Generally, polymerisation leads to the aU-cii polymer. At room temperature this changes to the thermodynamically stable ail-trans form. These two forms are geometrical isomers (see Section S2.1). Both are poor insulators, with the trans form having a conductivity similar to that of silicon (approximately 10 S m ), and the cis form with a conductivity similar to that of water (approximately 0.1 S cm ). 

Conducting organic polymers such as polyacetylenes, polyanilines and polypyrroles are of interest in electronic devices. One of the difficulties associated with their application is that they are degraded upon exposure to the atmosphere. For this reason, attempts have been made to prepare them encapsulated within zeolites, for example by polymerising acetylene over metal-exchanged zeolites. A recent report shows that polyacetylenes can also be prepared inside functionalised MOFs (see Section 10.3.3). It remains a challenge to prepare materials of acceptable properties for applications. 

Figure 10.5 Controlled polymerisation of methylacetylenes in the pores of the coordination polymer Cu2(pzdc)2(pyz) gives r 5 -polyacetylene due to the steric restrictions. [Reproduced from reference 33 with permission. Copyright 2006, Wiley-VCH Verlag GmbH Co. KGaA.]...

The first illustration of the theme is provided by reference to the paradigm for the semiconducting polymer field, polyacetylene. This curious material was first produced by the obvious route namely, direct addition polymerisation of acetylene over a Ziegler-Natta catalyst, indeed the reaction was first conducted in Natta s laboratories. The product, an intractable, air sensitive powder, was shown to have a predominantly trans vinylene microstructure. Two American industrial research chemists. Berets and Smith, demonstrated that compressed pellets of polyacetylene prepared by Natta s route were semiconductors whose conductivity could be varied by exposure to volatile donors like anunonia (conductivity decreases) or acceptors like iodine (conductivity increases). Subsequently, apparently as a result of a serendipitous event in Shirakawa s laboratory, it was found that interfacial polymerisation of acetylene at the surface of a high... 

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