Other Urea-Aldehyde Condensations

Urea reacts with a variety of mono- [29] and dialdehydes [30] to give either linear or cyclic products as shown in Eqs. (11) and (12) and Table VI. 

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Other types of resin modifiers compatible with resols may also be used. Examples include UF (urea-aldehyde condensation product) and epoxide. Japanese workers have found that the most effective and economical ingredients as modifiers for phenolic foam are resorcinol, o-cresol, and fulfuryl alcohol. 

This volume continues in the tradition of Volume I in presenting detailed laboratory instructions for the preparation of various types of polymers such as urea, melamine, benzoguanamine/aldehyde resins (amino resins-amino-plasts), phenol/aldehyde condensates, epoxy resins, silicone resins, alkyd resins, polyacetyls/polyvinyl acetals, polyvinyl ethers, polyvinyl pyrroli-dones, polyacrylic acids, and polyvinyl chloride. Polyvinyl acetate and related vinyl esters, allyl polymers, acetylene polymers, maleate and fumarate polymers, and several other addition-condensation polymer types will be covered at a later date in Volume III. 

In far too many instances trade-name polymer nomenclature conveys very little meaning regarding the structure of a polymer. Many condensation polymers, in fact, seem not to have names. Thus the polymer obtained by the step polymerization of formaldehyde and phenol is variously referred to a phenol-formaldehyde polymer, phenol-formaldehyde resin, phenolic, phenolic resin, and phenoplast. Polymers of formaldehyde or other aldehydes with urea or melamine are generally referred to as amino resins or aminoplasts without any more specific names. It is often extremely difficult to determine which aldehyde and which amino monomers have been used to synthesize a particular polymer being referred to as an amino resin. More specific nomenclature, if it can be called that, is afforded by indicating the two reactants as in names such as urea-formaldehyde resin or melamine-formaldehyde resin. 

One other novel approach to DHPMs has been described by Shutalev et al. and is outlined in Scheme 4.6 [135], This synthesis is based on the condensation of readily available a-tosyl-substituted (thio)ureas 16 with the (in situ prepared) eno-lates of acetoacetates or 1,3-dicarbonyl compounds. The resulting hexahydropyri-midines 17 need not be isolated and can be converted directly into DHPMs 14. This method works particularly well for aliphatic aldehydes and thioureas and produces high overall yields of the desired target compounds. 

A cationic starch can be prepared by blending a condensate of formaldehyde plus an inorganic ammonium salt with starch and heating at 80 °C for up to 1 h.1316 A great interest was developed with urea-formaldehyde resins that were made to react with such polyalcohols as starch.1317-1319 It was reported that the reaction of starch with urea-formaldehyde resin required an acidic catalyst592,1320-1325 and the use of such dispersants as polyphosphates.1326 Ammonium metaphosphate catalyzed the reaction without the addition of any other acid catalyst.1327 A product that formed a paste was produced by controlling the proportion of starch to aldehyde (either up to 20% of formaldehyde or up to 30% of acetaldehyde) and urea (up to 15%) at pH 2 1.1328... 

This reaction has been modified from acid-catalyzed cyclization of uredo acids from palladium catalyzed MCR among aldehydes, carbon monoxide, and ureas and from Ugi five-component condensation. Alternatively, hydantoins can also be synthesized via other methods, such as the 1,3-Dipolar Cycloaddition of l-oxa-4-azabutadiene and aryl isocyanates and the decomposition of barbituric acids in alcohol. ... 

The largest class of nonionic surfactants is the polyoxyethylene condensates, but these have only a moderate effect and are not widely used. Silicone fluids may be considered as nonionic surfactants although they are used as anticaking agents for many powders, their use on fertilizers is limited due to their high cost. Other nonionic surfactants include fatty acid esters, substituted ureas, and aldehydes and ketones with low molecular weight [115,1161. 

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