Aromatic cross-links

Drugs can be administered locally and selectively to the colon if they are enclosed in a dosage form, such as a capsule, coated with an azo-aromatic cross-linked polymer... 

Other Reactants. Other reactants are used in smaller amounts to provide phenoHc resins that have specific properties, especially coatings appHcations. Aniline had been incorporated into both resoles and novolaks but this practice has been generally discontinued because of the toxicity of aromatic amines. Other materials include rosin (abietic acid), dicyclopentadiene, unsaturated oils such as tung oil and linseed oil, and polyvalent cations for cross-linking. 

Solubility. Cross-linking eliminates polymer solubiUty. Crystallinity sometimes acts like cross-linking because it ties individual chains together, at least well below T. Thus, there are no solvents for linear polyethylene at room temperature, but as it is heated toward its (135°C), it dissolves in a variety of aUphatic, aromatic, and chlorinated hydrocarbons. A rough guide to solubiUty is that like dissolves like, ie, polar solvents tend to dissolve polar polymers and nonpolar solvent dissolve nonpolar polymers. 

In addition to combined hydrogen and oxygen, carbon blacks may contain as much as 1.2% combined sulfur resulting from the sulfur content of the aromatic feedstock that contains thiophenes, mercaptans, and sulfides. The combined sulfur appears to be inert and does not contribute to sulfur cross-linking during the vulcanization of mbber compounds. 

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). 

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