Dimethylol urea

Urea - formaldehyde polymers. Formalin and urea (usually in the molecular proportions of 3 2) condense in the presence of ammonia, pyridine or hexamine to give urea - formaldehyde polymers, known commercially as Bedle or Plaskon, and are widely used as moulding powdens. It is believed that the intermediate products in the condensation are methylol-urea and dimethylol-urea ... 

Polymerisation may occur as a result of dehydration of these compounds to methylene and dimethylene urea or more probably by a stepwise loss of water between the molecules of methylol and dimethylol-urea. 

Urea-formaldehyde resins are usually prepared by a two-stage reaction. The first stage involves the reaction of urea and formaldehyde under neutral or mildly alkaline conditions, leading to the production of mono and dimethylol ureas (Figure 24.1). The ratio of mono to dimethylol compounds will depend on the urea-to-formaldehyde ratio and it is important that there should be enough formaldehyde to allow some dimethylol urea formation. 

Since -aa NH groups (as found in dimethylol urea) are apparently less reactive the initial reaction products appear to be based on linear polymers of the form... 

The nucleophilic addition reaction of urea to formaldehyde produces mainly monomethylol urea and some dimethylol urea. When the mixture is heated in presence of an acid, condensation occurs, and water is released. This is accompanied by the formation of a cross inked polymer ... 

Urea undergoes reaction with formaldehyde in mild alkaline condition to yield monomethylol urea, dimethylol urea and trimethylol urea-respectively, as depicted below ... 

Another of the early thermo-setting resins was the urea formaldehyde resin developed by American Cyanamid. Urea and formaldehyde gave methylol and dimethylol urea which on heating, further condensed to give the colorless resin. The technology of this process was well worked out, but the chemistry was still not completely understood. The colorless resin has been used to make many varieties of decorative materials and some essentially unbreakable dishes, among other uses. 

With urea, formaldehyde forms two stable IV.O-hemiacetals (Figure 9.25) a 1 1 adduct ( methylol urea ) and a 1 2 adduct ( dimethylol urea ). When they are heated, both compounds are converted to macromolecular IV.lV-acetals (Figure 9.26). A three-dimensionally cross linked urea/formaldehyde resin is produced it is an important plastic. 

Fig. 9.26. Mechanism of the formation of a urea/formalde-hyde resin from methylol urea (R1 = H in formula A possible preparation Figure 9.25) or dimethylol urea (R1 = HO—CH2 in formula A possible preparation Figure 9.25). The substituents R1, R2, and R3 represent the growing —CH2—NH— C(=0)—NH—CH2— chains as well as the derivatives thereof that are twice methylenated on N atoms.

Urea-Formaldehyde. These plastics became commercial about 1929. Urea and formaldehyde react very readily to form methylol compounds, mainly dimethylol urea. 

Urea-formaldehyde (U/F) products are readily synthesised from water solutions of urea and formaldehyde at pH 7.5-9. The resulting iV,iV-dimethylol urea (DMU) is often modified by further reaction at pH 8-9 with methanol to the more stable and liquid dimethylether of DMU (dimethoxymethyl urea) as shown in Fig. 5.1. These reactions are equilibrium reactions with significant concentrations of the starting compounds. These equilibria are the reasons for the high content of free and easily released formaldehyde found with U/F products. Because of their high reactivity, unmodified U/F finish baths must be used within a few hours. The high stiffness and firmness of the U/F finish can be important for rayon fabrics which often are considered too limp when compared with cotton. The U/F finish gives the best elastic resilience. ... 

KAURIT S is a urea-formaldehyde compound its composition is roughly that of dimethylol urea. The product is supplied in the form of white, fine powder with almost 100% active substance. 

KAURIT W consists of a dimethylol urea modified by etherification. It is supplied in the form of an approx. 80% paste that dissolves readily in warm water. KAURIT W is less reactive than KAURIT S, but it has far better liquor stability owing to the etherification. The bath stability of other, unmodified methylol-urea compounds can be improved markedly by addition of 30-50% of KAURIT W. 

See dimethylol urea methylol urea melamine resin urea-formaldehyde resin. 

Since groups (as found in dimethylol urea) are apparently less reactive... 

Since the original Tootal patent there has been much research on alteration of the properties of cellulosic materials by the formation of polymers in situ. The original formaldehyde urea method for the crease-resistant finish is probably still -the most commonly used. Dimethylol-urea is now used as the monomer instead of a mixture of urea and formaldehyde. It is the product of the reaction of one molecule of lurea with two molecules of formaldehyde ... 

The advantage of dimethylol-urea is that the correct quantities of formaldehyde and urea are available in a pre-prepared state. It also ensures that, on polymerization, there will be an extremely high yield of the completely cross-linked product shown in (2) which is free from amino or imino groups. Methylol ureas, however, are comparatively unstable, and for this reason there is a tendency to prefer the more stable methyl esters, such as shown in (3), which condense with the elimination of methyl alcohol ... 

It was observed that the last reaction works only when basic impurities are trapped by some added acetic acid or carbon dioxide. Later this stabilization of oxaziridine solutions by carbon dioxide was claimed in a patent. The amination occurs intramolecularly when the oxaziridine 40, formed from 34 and dimethylol urea, is treated with strong alkali. This amination gives rise to the parent compound of the diaziridines. ... 

The amination occurs intramolecularly when the oxaziridine 40, formed from 34 and dimethylol urea, is treated with strong alkali. This amination gives rise to the parent compound of the diaziridines.67... 

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. 

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