Hexamethylenetetramine, novolac crosslinking

Resole on the other hand, does not require hexamethylenetetramine, for crosslinking because resole type resin contains relatively large amounts of ether-linkages in its structure. It is, therefore, expected that a blend of polyesterimide and resole will result in a crosslinked product on heating at lower teannpera-ture than novolac. 

Finally, crosslinked structures of type VII may result from the hardening, for instance, of phenolic resins (503) through reaction of novolacs with hexamethylenetetramine, which is a preformed aminomethylating agent (see Table 31, Chap. III). 

Novolacs are crosslinked by additions of more formaldehyde to the soluble, thermoplastic materials. The additional formaldehyde can be in the form of paraform, an oligomer of formaldehyde that decomposes to formaldehyde upon heating. It can also come from hexamethylenetetramine, a condensation product of formaldehyde with ammonia ... 

Novolacs are thermoplastic materials, that need to be transformed by crosslinking reactions to get insoluble, nonmelting, thermally stable thermosets. Different crosslinking agents have been used for thermal curing, for instance l,3,5,7-tetiaazatricyclo[3.3.3. P Jdecane (hexamethylenetetramine), oxiranes (epoxides), diisocyanates, urea, melamine, urea methanal resins, melamine metfaanal resins, and imide precursors. Furthermore, photoreactive compounds crosslink novolacs with methacrylate and methacryloylchloride resins, respeetively by itradialion [1]. 

Novolacs can be transformed into insoluble, nomnelting, thermally stable fheimosets by crosslinking reaction with 1,3,5,7-tetraazatricyclo-[3.3.3. H ]-decane (hexamethylenetetramine), oxiiane (epoxides), diisocyanates, urea. 

Novolacs are thermoplastic materials that have to be cured by the addition of a crosslinker, such as paraformaldehyde or hexamethylenetetramine. About 10 to 15% hexa is required for optimum cure of a novolac having a phenol/formaldehyde ratio of 1 0.8. 

Phenol-formaldehyde novolac resins are formed by the incomplete polymerization of phenol and formaldehyde. Insufficient formaldehyde is present to allow complete cme. Complete crosslinking can be achieved by adding a powdered methylene donor such as hexamethylenetetramine and heat. Resorcinol-formaldehyde novolac liquid resins can be eured by the addition of powdered paraformaldehyde. 

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