Heterocyclic aromatic fiber

Diketene also is widely employed as a natural and synthetic fiber cross-linking agent, wood preservative and paper-sizing agent. Both it and /3-propiolactone have wide application as chemical intermediates. The synthetic applications of diketene for the synthesis of aromatic, heterocyclic and aliphatic compounds is exceptionally extensive (74ACR265). 

Azo dyes, characterized by the presence of one or more azo groups (-N=N-), are the most commercially important class of dyes. These compounds are synthesized using a diazoti-zation reaction in which a primary aromatic amine reacts with nitrous acid to form a diaz-onium salt. The diazonium compound then typically is coupled with phenols, napthols, aromatic amines, heterocycles, or a variety of other compounds containing active methylene groups. Azo dyes are used in acid, direct, disperse, fiber reactive, and mordant applications. 

The SPME selectivity of fibers coated with polyacrylate, carbowax-DVB or poly-DMS can be improved by working at pH 2 to extract organic acids such as phenols or at pH 12 to extract organic bases such as aromatic amines and aromatic heterocyclic compounds. The following recoveries of each analyte were attained by a polyacrylate fiber (best overall performance) immersed for 30 min in 2 mL of water, at pH 12, containing 10 p,g of... 

Kim and Reneker electrospun aromatic heterocyclic PBl polymer by electrospinning and produced birefringent fibers of approximately 300 nm in diameter (Kim and Reneker 1999). 

Many fluorescence sensors are based, not on direct fluorescence, but on the quenching of fluorescence. Molecular oxygen, for example, is one of the best col-lisional quenchers. Oxygen can quench the fluorescence from polycyclic aromatic hydrocarbons complexes of ruthenium, osmium, iridium, and platinum and a number of surface-adsorbed heterocyclic molecules. An oxygen sensor can be made by immobilizing the fluorophore in a thin layer of silicone on the end of a fiber-optic bundle. Sensors for SO-, haliilcs, H-O-, and several other molecules have been ba.sed on fluorescence quenching. 

Epoxy resins are among the most important of the high performance thermosetting polymers and have been widely used as structural adhesives and matrix for fiber composites. Epoxy resins are characterized by the presence of epoxide groups before cure, and they may also contain aliphatic, aromatic, or heterocyclic structures in the backbone. The epoxy group can react with amines, phenols, mercaptans. 

The novel polymers (end of 1960s and early 1970s) belong mostly to the HT group and their overall utility is limited. Many appear as special fibers, like aromatic polyamides and polyesters, polyimides and Parylene. The novel structures have rings (either aromatic or heterocyclic), in the main chain (para-phenylene is preferred over meta-phenylene). Substituting C—H bonds... 

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