Furfuryl alcohol, acid polymerization

However, the most important furan resins are those produced with 2-furfuryl alcohol, for example, the 2-furfuryl alcohol-formaldehyde-based resins, which are normally synthesized by a condensation reaction catalyzed by acidic sites and promoted by heat [224] or the poly(furfuryl alcohol) thermosetting resin that is usually synthesized by the cationic condensation of its monomer 2-furfuryl alcohol, which polymerizes exothermically in the presence of a catalyst such as acid and iodine in methylene chloride, producing black, amorphous, and branched and/or cross-linked structures [225],... 

A violent explosion occurs when furfuryl alcohol is polymerized with concentrated mineral acids such as HCl, H2SO4, or HNO3. 

Note Under strongly acidic conditions, furfuryl alcohol can polymerize with explosive violence. 

Furfuryl Alcohol Resins. Polymerization and cure, and copolymerization/cure with urea-formaldehyde and phenol-formaldehyde, are generally catalyzed by acids such as p-toluene sulfonic acid and zinc chloride. 

Furfural is a resin former under the influence of strong acid. It will self-resinify as well as form copolymer resins with furfuryl alcohol, phenoHc compounds, or convertible resins of these. Conditions of polymerization, whether aqueous or anhydrous, inert or oxygen atmosphere, all affect the composition of the polymer. Numerous patents have issued relating to polymerization and to appHcations. Although the resins exhibit a degree of britdeness, they have many outstanding properties a number of appHcations are discussed under "Uses."... 

Under acidic conditions, furfuryl alcohol polymerizes to black polymers, which eventually become crosslinked and insoluble in the reaction medium. The reaction can be very violent and extreme care must be taken when furfuryl alcohol is mixed with any strong Lewis acid or Brn nstad acid. Copolymer resins are formed with phenoHc compounds, formaldehyde and/or other aldehydes. In dilute aqueous acid, the predominant reaction is a ring opening hydrolysis to form levulinic acid [123-76-2] (52). In acidic alcohoHc media, levulinic esters are formed. The mechanism for this unusual reaction in which the hydroxymethyl group of furfuryl alcohol is converted to the terminal methyl group of levulinic acid has recendy been elucidated (53). 

Uses. Furfuryl alcohol is widely used as a monomer in manufacturing furfuryl alcohol resins, and as a reactive solvent in a variety of synthetic resins and appHcations. Resins derived from furfuryl alcohol are the most important appHcation for furfuryl alcohol in both utihty and volume. The final cross-linked products display outstanding chemical, thermal, and mechanical properties. They are also heat-stable and remarkably resistant to acids, alkaUes, and solvents. Many commercial resins of various compositions and properties have been prepared by polymerization of furfuryl alcohol and other co-reactants such as furfural, formaldehyde, glyoxal, resorcinol, phenoHc compounds and urea. In 1992, domestic furfuryl alcohol consumption was estimated at 47 million pounds (38). 

Furan resins are produced by the polymerization of furfural or furfuryl alcohol in the presence of acids (see Figure 15.8). The properties of these dark-colored resins are shown in Table 15.6. Furan resins have a relatively low heat deflection temperature (80 °C) and good mechanical properties. These materials, which are widely used as jointing materials for brick and tile, are characterized by excellent resistance to nonoxidizing acids, alkalis, and salts but are affected by the presence of oxidizing acids such as nitric acid. The furan plastics are also resistant at room temperature to nonpolar solvents, such as benzene, and to polar solvents, such as ethanol. 

An interesting group of composite membranes with very good properties is produced by condensation of furfuryl alcohol with sulfuric acid. The first membrane of this type was made by Cadotte at North Star Research and was known as the NS200 membrane [32], These membranes are not made by the interfacial composite process rather a polysulfone microporous support membrane is contacted first with an aqueous solution of furfuryl alcohol and then with sulfuric acid. The coated support is then heated to 140 °C. The furfuryl alcohol forms a polymerized, crosslinked layer on the polysulfone support the membrane is completely black. The chemistry of condensation and reaction is complex, but a possible polymerization scheme is shown in Figure 5.10. 

Oxidation of wood by HNO3 at ambient temperature that results in the formation of carboxylic acid groups on the surface has been substantiated (157). These carboxylic groups are sufficiently acidic to catalyze polymerization of furfuryl alcohol. 

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