Aromatic linking agents

An example of the importance of free-volume availabiUty on cross-linking has been reported in the evaluation of a trifunctional derivative of an ahphatic isocyanate which contains an aromatic ring, y -tetramethylxyUdene diisocyanate (TMXDI) [2778-42-9] C 4H N202, as a cross-linking agent for hydroxy-functional resins (15). 

There is, quite clearly, scope or a very wide range of epoxy resins. The nonepoxy part of the molecule may be aliphatic, cycloaliphatic or highly aromatic hydrocarbon or it may be non-hydrocarbon and possibly polar. It may contain unsaturation. Similar remarks also apply to the chain extension/cross-linking agents, so that cross-linked products of great diversity may be obtained. In practice, however, the commercial scene is dominated by the reaction products of bis-phenol A and epichlorohydrin, which have some 80-90% of the market shtu"e. 

A number of aromatic amines also function as cross-linking agents. By incorporating the rigid benzene ring structure into the cross-linked network, products are obtained with significantly higher heat distortion temperatures than are obtainable with the aliphatic amines. 

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). 

Succinimidyloxycarbonyl-a-methyl-a-(2-pyridyldithio)toluene (SMPT) is a heterobifunctional cross-linking agent that contains an amine-reactive NHS ester on one end and a sulfhydryl-reactive pyridyl disulfide group on the other. SMPT is therefore an analog of SPDP that differs only in its cross-bridge which contains an aromatic ring... 

Ferrocenylboron-capped macrobicyclic iron(II) acyclic, alicyclic and aromatic dioximates as potential electron carriers were synthesized by direct template reactions using ferrocenylboronic acid as the cross-linking agent [66]. 

Some effective cross-linking agents are less suitable for the conjugation of enzyme to antibody. Diazonium salts of aromatic compounds react preferentially with histidine and tyrosine which are very often located in or near the active site of the enzyme. Protecting the active sites with inhibitors (Jansen et al., 1971) is often cumbersome and, consequently, not very popular. 

The concept of an asphaltene model that incorporates smaller polynuclear aromatic systems is more in keeping with the types of systems that occur in nature. Indeed, smaller polynuclear aromatic (and pseudoaromatic) systems are capable of producing high yields of thermal coke either because of the heteroatom content (87) or because of the presence of pendant alkyl moieties that have the capability of forming the internuclear cross-links (88) that can lead to coke. In this latter case, it is likely that the indigent alkyl chains can interact in this manner, or shorter alkyl chains, formed by thermolysis, can play the role of cross-linking agents. 

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