Triazine ring cross-linked

Triazine Ring Cross-linked Polyimides and Refractory Materials Derived from Them... 

Melamine resins were introduced about ten years after the Beetle molding compound. They were very similar to those based on urea but had superior quaHties. Henkel in Germany was issued a patent for a melamine resin in 1936 (7). Melamine resins rapidly supplanted urea resins and were soon used in molding, laminating, and bonding formulations, as well as for textile and paper treatments. The remarkable stabiHty of the symmetrical triazine ring made these products resistant to chemical change once the resin had been cured to the insoluble, cross-linked state. 

A polyvinyl alcohol is obtained by suspension polymerization of vinyl acetate and the cross-linking agent, triallyl isocyanurate, with a triazine ring followed by alkali hydrolysis. The polyvinyl alcohol gel is used as packing for gel-... 

Cibacron Blue is a blue, polyaromatic, sulfonated dye (Fig. 6). It can be attached, as an affinity li nd, to solid matrix supjmrts (e.g. dextran, agarose) by the reaction of the triazine ring with free hydroxyl groups of the supports. The conditions of this triazine coupling method have been described by Bohme Such a dye affinity sorbent is also produced commercially, e.g. under trade name Blue Sepharose CL-6B (Cibacron Blue F3G-A covalently bound to the cross-linked agarose gel Sepharose CL-6B ) by Pharmacia, Sweden. 

The graphite fiber reinforced triaryl-s-triazine ring (TSTR) cross-linked polyimides with ring-chain structures have good mechanical properties at elevated temperatures. On pyrolysis, the TSTR cross-linked polyimides were converted to refractory type materials which are believed to be graphitic type ladder polymers containing some nitrogen in their cyclic structures. 

The polyimide class of polymers are known to possess a high degree of thermal stability. They decompose in an inert atmosphere around 500°C and in air about 400°C as indicated by thermo-gravimetric analysis (1). Because of the great thermal stability of 2,4,6-triphenyltriazine (2J (decomposes above 486°C), copolymerization of this compound with imides should lead to enhanced heat resistant materials in the form of triaryl-s-triazine ring (TSTR) cross-linked (XL) polyimides. 

Terpolymers of tetrafluoroethylene, perfluoromethyl vinyl ether, and small amounts of a cross-linking termonomer, such as, for example, perfluoro(4-cyanobutyl vinyl ether), are free radically copolymerized in emulsion. Vulcanization occurs by cyclotrimerization of the cyano groups to s-triazine rings. The elastomer has a glass transition temperature of —12 C and a brittle temperature of —39° C. It is very resistant to weathering and possesses a good low-temperature flexibility. 

Triazine and Other Heterocyclic Ring Formation. Several types of reactions can be used to form heterocyclic rings in which multiple C-N bonds contribute high thermal stability. When these are used to cross-link heat-stable oligomers, the resulting thermoset polymers may have high thermal stability and other useful properties. These include cyanate/cyanurate, isocyanate/isocyanurate, hexaazatriphenylene trianhydride, and phtha-lonitrile/phthalocyanine. 

Tris(alkoxycarbonylamino)triazine (TACT), a mixed methyl and butyl carbamate derivative of melamine, acts as an alcohol blocked isocyanate (21). TACT is much more reactive than conventional alcohol blocked isocyanates, since it is activated by the triazine ring. It cross-links hydroxy-functional acrylics at 125°C in 30 min, comparable to (or lower than) oxime blocked isocyanates. The reaction is not catalyzed by tin compounds it is catalyzed to a small extent by dodecylbenzene sulfonic acid. 

Upon heating, melamine-based salts dissociate, and re-formed melamine volatilizes in a manner similar to pure melamine. However, in the case of melamine salts, a larger portion of melamine undergoes progressive condensation than does pure melamine therefore, the condensed-phase contribution of the salts is larger. If the anion contains phosphorus, the phosphoric acid released will phos-phorylate many polymers and produce a flame retardant effect similar to that of other typical phosphorus-based additives (see above). Melamine condensates and phosphoric acid react further at temperatures above 600° C, where triazine rings are opened and cross-linked. A (PON) type of structure known as phosphorus oxynitride is formed. Phosphorus oxynitride is very thermally stable and in some polymers can contribute to condensed-phase mechanisms. ... 

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