Methylol melamine

The chemistry of melamines and phenoHcs is quite similar. In both cases formaldehyde [50-00-0] is added to the reactive sites on the patent ring to form methylol phenols (3) or methylol melamines (4) (see Phenolresins Aminoresins). There ate six reactive sites on the triazine ring of melamine [108-78-1] (1) so it is possible to form hexamethylolmelamine. However, the most common degree of methylolation is 1.5—2.0. The ortho and para positions of phenol ate active thus phenol can be trimethylolated (2). However, as with melamine, lower degrees of methylolation such as 1.2—2.5 ate... 

For resistance to actinic degradation, the use of certain forms of titanium oxide is an alternative to chrome salts. Another approach has been the use of polymerized methylol melamine on cotton (145). In this case, the action of sunlight leads to gradual breakdown of the melamine polymer after several years. After this, actinic degradation of cotton proceeds as it does in unprotected cotton. 

Methylolated melamine, cotton cross-linking agent, 8 26 Methylolation, in amino acid resin formation, 2 624... 

Figure 7.1 Reaction of melamine with formaldehyde and subsequent dimerization of the methylolated melamine monomers.

Pentaerythritol, monomer, dimer, trimer Phenol-formaldehyde resins Methylol melamine... 

Melamine, a white powder, was discovered and identified by Liebig in 1834 but commercial manufacture came only in 1939, by Cyanamid Company of America with dicyandiamide as raw material. Melamine is 2,4,6-triamino-l,3,5-triazine with a structure as shown in Figure 53. On reaction with formaldehyde in aqueous solution the melamine powder dissolves rapidly on heating to form various methylol melamines, as in Figure 54. After further heating and the elimination of water the methylol melamines condense to form resinous polymers. 

Melamine chemistry begins with the addition of 2-3 mols of formaldehyde to form methylol melamines. 

The combination of resonance stabilization in the melamine heterocycle, and the high cross-linking between methylol melamines and with the other polymers, all produce the outstanding properties which make it a valuable specialty member of the thermoset plastics spectrum. 

Another category of durable hand builders are formaldehyde-containing thermosetting polymers. These products are usually supplied as dispersions or aqueous solutions of precondensates of urea or melamine with formaldehyde, for example di-methylol urea or di- to hexa-methylol melamine and their methyl ethers. The thermosetting polymers are comparatively inexpensive and provide fabrics with stiffness and resilience. However, they have a tendency to reduce abrasion resistance, yellow after exposure to heat, and release formaldehyde. Melamine-based hand builders are more highly crosslinked than urea-based products and are accordingly more durable. Butylated urea condensates are especially useful for rayon fabrics (see also Chapter 5 Easy-care and durable press finishes of cellulosics). 

Because these fire-retardant salts are water-soluble and subject to leaching, several new methods have been developed which provide a water-resistant or permanent treatment for cotton fabrics and cellu-losic materials. Perkin developed a process involving successive treatment with sodium stannate and ammonium sulfate, which precipitates stannic oxide in the cellulose libers. Antimony oxide in combination with vinyl chloride or other chlorinated polymers has also been found effective. A more recent approach to this problem involves application of fire-retardant resin-forming or cross-linking compounds. " These include materials and methods based on the copolymerization of tetrakis(hydroxymethyl)phosphonium chloride and methylol — melamine, the reaction of bromoform and triallyl phosphate to form a cross-linked polymer, and the cross-linking reaction of tris(l-aziridinyl)phosphine oxide with cellulose, or its copolymerization with tetrakis(hydroxymethyl)phosphonium chloride and other materials. ... 

After hydrolysis, the silanol groups are able to condense with the reactive methylol groups in hydroxymethylated di- and trimelamine as well as with unbridged methylolated melamine species (Scheme 4) to yield the rigid and infusible three-dimensional networks between resin and silane after final curing. Of course, reactions between silanol groups and hydroxyl groups of the cellulose in the paper would seem to be possible, but this has never been proven without doubt. 

Melamine will react with formaldehyde to form methylol melamines. 

For convenience, it is usually referred to as THPC. Reeves and Guthrie Dyer III., 1954,567) reported that fire resistance of good fastness to washing could be obtained by applying THPC together with urea and methylol melamine. An example quoted by Perfect loc. cit.) is as follows ... 

The acrylic resin used was Rohm and Haas Co.s QR-496 ( 4), so the exact nature of the polymer is not known. It is hydroxy functional, thus requiring an aminoplast for proper cure commercially modified hexa-methylol melamine resin was used for this purpose. During the first part of the investigation the acrylic resin was used without the melamine resin, but for final evaluation it was incorporated to give a more realistic commercial coating system. 

The reaction is carried out under slightly alkaline conditions and will yield crystalline derivatives of dimethylol urea or methylol melamines containing up to six methylol groups. 

A melamine laminating resin used to saturate the print and overlay papers of a typical decorative laminate might contain two moles of formaldehyde for each mole of melamine. In order to inhibit crystallization of methylol melamines, the reaction is continued until about one-fourth of the reaction product has been converted to low molecular weight polymer. A simple determination of free formaldehyde may be used to foUow the first stage of the reaction, and the build-up of polymer in the reaction mixture may be followed by cloud-point dilution or viscosity tests. 

Reaction of melamine (2,4,6-triamino-l,3>5-triazine) with neutralized formalin at about 80-100°C leads to the production of a mixture of water-soluble methylol melamines. The methylol content of the mixture depends on the initial ratio of formaldehyde to melamine and on the reaction conditions. Methylol melamines possessing up to six methylol groups per molecule are formed (Figure 4.27). 

On further heating, the methylol melamines undergo condensation reactions, and a point is reached where hydrophobic resin separates out. The rate of resinification depends on pH. The rate is minimum at about pH 10.0-10.5 and increases considerably both at lower and higher pH. The mechanism of resinification and cross-linking is similar to that observed for urea-formaldehyde (Figure 4.26) and involves methylol-amine and methylol-methylol condensations. 

There are many examples in the literature of the structural characterization of polymeric systems by FD-MS. Some of these will be briefly mentioned here. Saito and coworkers in Japan have studied a number of polymers by FD-MS. FD spectra were used to identify various poly(ethylene glycol) and poly(pro-pylene glycol) initiators (water, ethyleneimine, glycerol, sorbitol, sucrose). Structures of bisphenol A-based epoxy resins were elucidated. The degree of methylation in methylol melamine resins was assessed. Various novalak resins (made from phenol, alkylphenols, and epoxidized phenols) were characterized. Styrene polymerized with various initiators and chain transfer agents was studied in some cases deuterium labeling was used to help... 

Saito, J., Toda, S., and Tanaka, S., Chemical structural investigation of methylated methylol melamine resins by field desorption mass spectrometry, Netsu Kokasei jushi, 1,18,1980. 

Chert). Descrip. Butoxymethyl methylol melamine (60%) in n-butanol Uses Crosslinking agent for alkyd/polyester or acrylic resins, for use in solv.-borne systems, industrial stoving finishes, automotive finishes, metal decorating and dipping enamels, polymeric/resinous food-contact coatings... 

Chem. Descrip. Isobutoxymethyl methylol melamine resin (60%) in isobutanol... 

Chem. Descrip. Methoxymethyl methylol melamine resin (84%) in isobutanol/isopropanol... 

Chem. Descrip. Butoxymethyl methylol melamine resin (65%) in n-bu-tanol... 

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