Hexamethylenetetramine HEXA

Hexamethylenetetramine. Hexa, a complex molecule with an adamantane-type stmcture, is prepared from formaldehyde and ammonia, and can be considered a latent source of formaldehyde. When used either as a catalyst or a curative, hexa contributes formaldehyde-residue-type units as well as benzylamines. Hexa [100-97-0] is an infusible powder that decomposes and sublimes above 275°C. It is highly soluble in water, up to ca 45 wt % with a small negative temperature solubiUty coefficient. The aqueous solutions are mildly alkaline at pH 8—8.5 and reasonably stable to reverse hydrolysis. 

We now compare theoretical predictions with experimental results obtained using silica sand coated with a 4% resin consisting of 100 parts by weight of a phenol-formaldehyde novolac and 5, 10, or 15 parts of hexamethylenetetramine (hexa) as hardener (Aranguren et al., 1984). 

These prepolymers, called novolacs, are dehydrated, reduced to a poAvder and then blended with about 10% by weight hexamethylenetetramine ( hexa, Eq. 21.32). Hexa is made by reacting... 

In connection with the present study and with other work relating to crystal growth processes, it was thought necessary to measure the vapor pressure of hexamethylenetetramine ( hexa ) (I). 

The novolac (two-stage) resins are made with an acid catalyst, and only part of the necessary formaldehyde is added to the reaction kettle, producing a mole ratio of about 0.81. The rest is added later a hexamethylenetetramine (hexa), which decomposes in the final curing step, with heat and moisture present, to yield formaldehyde and ammonia, which act as the catalyst for curing. 

Novolac resins are produced from an excess of phenol (F/P<1) to form linear polymers, as illustrated in structure 2, with molecular weights of 200-5000 and glass-transition temperatures of 45-70°C. In two-stage novolac systems cross-linking is accomplished by reaction with hexamethylenetetramine (hexa), which is prepared from formaldehyde and ammonia and may he considered a latent source of formaldehyde. 

The mean molecular weights of novolacs are usually about 1000 or less. Novolac can react further with formaldehyde [from paraformaldehyde or hexamethylenetetramine (hexa)] to give products that are considerably cross-linked and are said to be cured," thermoset, or thermohardened. 

Novolacs with some branched molecules [61] are produced by the reaction of 1.0 mole of phenol and 3.0 moles of formaldehyde (37% aqueous solution) using 0.06 mole of calcium hydroxide and heating at SO C until 2.4 moles of formaldehyde have reacted. Then 2.6 moles of phenol are added and the mixture is neutralized with dilute sulfuric acid. Then more acid is added and a novolac is prepared in the usual manner, as described above. This novolac cures faster with hexamethylenetetramine (Hexa) and does not produce a foamy mass [61]. 

Usually hexamethylenetetramine (hexa) is used at 0% of the novolac resin. Resin and hexa are ground together before curing the resin. These mixes are stable in the dry state. The physical properties of the cured resole or novolac reach a maximum degree of cross-linking at or near approximately 1.5 1.0 ratio of formaldehyde to phenol. 

The major curing agent for two-stage resins is hexamethylenetetramine (hexa) [89]. The hexa reacts to form bis- and // /5(hydroxybenzyl)amine and/or polynuclear nitrogen derivatives. At elevated temperatures the nitrogen products are unstable and may decompose into other products such as azomethines. 

Cl2H36Cr2MgN80i3, Magnesium dichromate hexamethylenetetramine hexa-hydrate, 40B, 554... 

HRH Systems. A review of currently available bonding agents such as HRH and modifications thereof, is given by Weaver." HRH designates the use of hexamethylenetetramine (hexa), resorcinol, and a hydrated silica as additives to rubber in order to improve adhesion to brass coated wire. Normally about 1.5 phr hexa, 2.5 phr resorcinol, and 15 parts of silica are added to a wire skim stock. Pre-... 

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