POLYPHENYLENE ACETYLENE

Polyphenylene Acetylene or Si-triisopropyl 1,8,9-T rihyd roxyanth racene Ag Not stated 180... 

Hsieh [116] attempted to prepare polyphenylene-acetylene (PPA) via bromination and dehydrobromina-tion of PPV (Scheme 16). Although the bromination step went largely as expected, elimination of the halogen atoms proved troublesome. Base treatment gave hydrolysis and bond cleavage rather than elimination. Instead,... 

Common conductive polymers are poly acetylene, polyphenylene, poly-(phenylene sulfide), polypyrrole, and polyvinylcarba2ole (123) (see Electrically conductive polymers). A static-dissipative polymer based on a polyether copolymer has been aimounced (124). In general, electroconductive polymers have proven to be expensive and difficult to process. In most cases they are blended with another polymer to improve the processibiUty. Conductive polymers have met with limited commercial success. 

The c/s-dihydroxylation reaction catalyzed by these dioxygenases is typically highly enantioselective (often >98% ee) and, as a result, has proven particularly useful as a source of chiral synthetic intermediates (2,4). Chiral cis-dihydrodiols have been made available commercially and a practical laboratory procedure for the oxidation of chlorobenzene to IS, 2S)-3-chlorocyclohexa-3,5-diene-l,2-c diol by a mutant strain of Pseudomonas putida has been published (6). Transformation with whole cells can be achieved either by mutant strains that lack the second enzyme in the aromatic catabolic pathway, cw-dihydrodiol dehydrogenase (E.C. 1.3.1.19), or by recombinant strains expressing the cloned dioxygenase. This biocatalytic process is scalable, and has been used to synthesize polymer precursors such as 3-hydroxyphenylacetylene, an intermediate in the production of acetylene-terminated resins (7). A synthesis of polyphenylene was developed by ICI whereby ftie product of enzymatic benzene dioxygenation, c/s-cyclohexa-3,5-diene-1,2-diol, was acetylated and polymerized as shown in Scheme 2 (8). 

Soluble polyphenylenes with a branched structure (36) were prepared (equation 34) from diethynylbenzene and phenylacetylene by trimerization of the acetylene group in the presence of Ziegler catalysts . The oligomers (called H-resin ) can be cross-linked on heating to yield thermally and chemically stable resins. ... 

A polymer with sequence of conjugated double bonds, such as poly acetylene, polyphenylene, and... 

SiLK dielectric resins involve the synthesis of crosslirJced polyphenylenes by the reaction of polyfimctional cyclopentadienone and polyftinctional acetylene-conatining materials. Polyphenylenes are known to have excelloit thermal stability. Typically, however, polyphenylenes need to be substantially substituted in order to achieve solubility and the processability. By preparing the polyphenylenes from cyclopentadienone and acetylene-containing monomers. 

The years that followed saw the synthesis of a bewildering number of conjugated polymers and copolymers from a wide variety of aromatic, heteroaromatic, and acetylene monomers with and without substituents, that were converted into their respective conductive forms with the aid of equally numerous oxidizing agents or Br0nsted acids. These highly conductive polymers include the polyacetylenes (PAc), polypyrroles (PPy), polythiophenes (PTh), polyphenylenes (PPP), and polyanilines (PAni). The conductivities achieved range from = 10" S/cm (intrinsic semiconductors) to =10 S/cm. 

The synthesis of polyphenylene ethinylene by a Pd/Cu catalyzed reaction was described by Marvel ct al. (75). The solubility problems of the para structure were reduced by the synthesis of the meta products. Soluble para connected polyphenylene ethinylene were synthesized by Schulz and Giesa in 1990 14), Trimethylsilylacetylene have been used to avoid the preparative problems of stoichiometric use of acetylene. 

The educt of acetylene with acetone allows a simple synthesis of polyphenylene ethinylene (77). The absorption of these polymers is in the same range as polyphenylene vinylene. This absorption is reach at a polymerization degree 7-8 also in this case. Oligomers can be used as active components in LED films. The flexibility of catalytic reactions makes a wide variety of derivatives available. 

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