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Phenol-formaldehyde resins acid-catalyzed

Condensations with carbonyl compounds phenol-formaldehyde resins. Acid or base catalyzes electrophilic substitution of carbonyl compounds in ortho and para positions of phenols to form phenol alcohols (Lederer-Manasse reaction). [Pg.448]

Phenol-formaldehyde resins are the oldest thermosetting polymers. They are produced by a condensation reaction between phenol and formaldehyde. Although many attempts were made to use the product and control the conditions for the acid-catalyzed reaction described by Bayer in 1872, there was no commercial production of the resin until the exhaustive work by Baekeland was published in 1909. In this paper, he describes the product as far superior to amber for pipe stem and similar articles, less flexible but more durable than celluloid, odorless, and fire-resistant. ° The reaction between phenol and formaldehyde is either base or acid catalyzed, and the polymers are termed resols (for the base catalyzed) and novalacs (for the acid catalyzed). [Pg.346]

A Friedel-Crafts-type reaction of phenols under basic conditions is also possible. Aqueous alkaline phenol-aldehyde condensation is the reaction for generating phenol-formaldehyde resin.34 The condensation of phenol with glyoxylic acid in alkaline solution by using aqueous glyoxylic acid generates 4-hydroxyphenylacetic acid. The use of tetraalkylammonium hydroxide instead of sodium hydroxide increases the para-selectivity of the condensation.35 Base-catalyzed formation of benzo[b]furano[60]- and -[70]fullerenes occurred via the reaction of C60CI6 with phenol in the presence of aqueous KOH and under nitrogen.36... [Pg.208]

Copolymers of furfural with phenol or phenol-formaldehyde polymers have been available commercially for many years. Since the acid-catalyzed reaction of furfural and phenol has been difficult to control, most industrial applications involve the use of alkaline catalysts. Furfural-phenol resins are used for their alkali resistance, enhanced thermal stability, and good electrical properties compared to phenol-formaldehyde resins. [Pg.408]

Figure 14 Acid-catalyzed formation of a phenol-formaldehyde resin. Figure 14 Acid-catalyzed formation of a phenol-formaldehyde resin.
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. [Pg.374]

Furan no-bake resins are two-component, r.t.-cur-ing, acid-catalyzed systems of furfiiryl alcohol prepolymer with additional monomer. Hot and warm box resins are mainly based on urea-modified fur-ftiryl alcohol-formaldehyde condensates that are cured at 100-170 °C. Also phenol-formaldehyde resins, modified with furfiiryl alcohol, are used. In cold box binder systems, the sand is mixed with a low-viscosity fiiran resin and a peroxide. The core is formed, and SO2 is blown into or generated in situ in the sand to cure the resin rapidly. [Pg.112]

Phenolic resins were discovered by Baeyer in 1872 through acid-catalyzed reactions of phenols and acetaldehyde. Kleeberg found in 1891 that resinous products could also be formed by reacting phenol with formaldehyde. But it was Baekeland who was granted patents in 1909 describing both base-catalyzed resoles (known as Bakelite resins) and acid-catalyzed novolac products.2... [Pg.375]

Phenolic Resins. Phenolic resins [9003-354] (qv) are thermosets prepared by the reaction of phenol with formaldehyde, through either the base-catalyzed one-stage or the acid-catalyzed two-stage process. The liquid intermediate may be used as an adhesive and bonding resin for plywood, particle board, fiberboard, insulation, and cores for laminates. The physical properties for typical phenolic laminates made with wood are listed in Table 1. [Pg.328]

Two-stage resins (novolacs) are produced by the acid-catalyzed reaction of phenol and a portion of the required formaldehyde. Tire resin product is brittle at room temperature. It can be melted, but it will not crosslink. Novolacs can only be cured by the addition of a hardener, almost always formaldehyde supplied as hexamethylene tetramine. Upon heating, the latter compound decomposes to yield ammonia and formaldehyde. [Pg.1275]

Acid Catalyzed Condensation Polymerizations. The strong protonic acids produced by the photolysis of onium salts I-III can also be employed to catalyze the condensation of phenolic, melamine, and urea formaldehyde resins. Very durable photoresists based on these inexpensive and readily available resins can be made. Such resists generally require a postbake prior to development to complete the condensation and to enhance image formation. [Pg.6]

Phenolic resins, introduced in 1908, are formed by either base- or acid-catalyzed addition of formaldehyde to phenol to give ortho- and para-substituted products. The nature of these products depends largely on the type of catalyst and the mole ratio of formaldehyde to phenol. In resole formation, excess formaldehyde is reacted with phenol under basic conditions. The initial reaction products are ortho- and para-substituted mono-, di-, and trimethylolphenols ... [Pg.462]

Phosphoric acid, or more commoifly ammonium chloride, is used as a hardener for UF resin adhesives. Ammonium chloride reacts with formaldehyde to produce hexamine and hydrochloric acid, and the latter catalyzes the curing of the resin. In the manufacture of plywood a resin (with U/F molar ratio typically 1 1.8) mixed with hardener is applied to wood veneers, which are then plied together and pressed at 95-110°C under a pressure of 200-800 psi (1.38-5.52 MPa). The UF resin-bonded plywood is suitable for indoor applications but is generally unsuitable for outdoor use. For outdoor applications phenol-formaldehyde, resorcinol-formaldehyde, or melamine-formaldehyde resins are more suitable. [Pg.475]

The phenolic resins that form in acid-catalyzed condensations of phenols with formaldehyde are different from resols. At pH below 7, protonation of the carbonyl group of formaldehyde takes place first and is followed by electrophilic aromatic substitution at the ortho and para positions of the phenol. The initial steps of the reactions also take place in water. Here, however, a molar excess of phenol (1.25 1) must be used, because reactions on equimolar basis under acidic conditions form crosslinked resins. At a ratio of 8 moles of formaldehyde to 10 moles of phenol, novolacs of approximate molecular weight 850 form. When the ratio of formaldehyde to phenol is 9 10, a molecular weight of approximately 1000 is reached. This appears to be near the limit, beyond which crosslinking results. The reaction is as follows ... [Pg.346]

The phenolic-based resin compounds are among the most widely used and well-known thermosets. Phenols react with aldehydes to give condensation products if there are free positions in the benzene ring - ortho and para to the hydroxyl group. Formaldehyde is the most reactive and is used almost exclusively in commercial production. The reaction is always catalyzed, either by acids or bases. The nature of the product greatly depends on the type of catalyst and the mole ratio of the reactants. Refer to Novolac Resins. [Pg.212]

The phenolic resins are condensation products of phenol and formaldehyde [144-146, 148]. These materials were among the earliest commercial synthetic plastics. Two different methods [144-146] are used to prepare them. In the first one, the condensations are base catalyzed, while in the second one, they are acid-catalyzed. The products formed with basic catalysts are called resols and with acidic ones novolacs. Phenolic resins are used widely in coatings and laminates. The pure resins are too friable for use as structural materials by themselves. They become useful plastics, however, when filled with various fillers. [Pg.483]

Other relevant reactions of resin acids are those involving their addition to formaldehyde and/or phenols. Formaldehyde adds to abietic acid to form complex mixtures containing mono and dihydroxymethyl derivatives [28-31]. Under alkaline conditions, the formation of the mono derivative is favoured, whereas in acetic acid, the dihomologue (isolated as acetate) is the major product (Fig. 4.10). More recently, studies of the acid-catalyzed condensation of abietic acid with formaldehyde showed that, under such conditions the reactions mixtures were predominantly composed of trimeric stmctures [26, 32]. [Pg.73]

PolyaCGtal. Polyacetals thermally decompose by an acid-catalyzed depolymerization process starting at the chain ends (see Acetal Resins). The polymer structure is stabilized by end capping and introdncing comonomers to interrupt the unzipping. The process is autocatalytic since the liberated formaldehyde is easily oxidized to formic acid, which is a prodegradant. Formaldehyde scavengers and phenolic antioxidants are typically used in polyacetal formulations (42). [Pg.633]

Epoxy NovolaC Resins. Epoxy novolacs are multifunctional epoxies based on phenolic formaldehyde novolacs. Both epoxy phenol novolac resins (EPN) and epoxy cresol novolac resins (ECN) have attained commercial importance (53). The former is made by epoxidation of the phenol-formaldehyde condensates (novolacs) obtained from acid-catalyzed condensation of phenol and formaldehyde (see Phenolic Resins). This produces random ortho- and para-methylene bridges. [Pg.2676]

Phenol has unique chemical properties due to the presence of a hydroxyl group and an aromatic ring, which are complementary in that they facilitate both electrophilic and nucleophilic reactions. The aromatic ring of phenol is highly reactive towards electrophilic snbstitntion, which assists its acid-catalyzed reaction with formaldehyde. Phenol is a weak acid and easily forms sodium phenoxide (NaPh) in a base-catalyzed medinm. In the presence of sodium phenoxide, the nucleophilic addition of the phenolic aromatic ring to the carbonyl group of formaldehyde occurs. Thus, phenol can react with formaldehyde under acidic or basic conditions, leading to either novolac or resole resins (Weber and Weber, 2010). [Pg.13]

The ENR was prepared by two step reactions. The first step was involved in the formation of novolac resin through condensation of phenol and formaldehyde under oxalic acid catalyzed with the molar ratio of phenol to formaldehyde was 1 0.8. In the second step, the epoxidation of previously prepared novolac resin was carried out by reacting novolac with excess of epichlorohydrin with 1 8 molar ratio under 40 % sodium hydroxide catalyst (Saw et al. 2011b, 2012). The schematics of synthesis are shown in Fig. 1. [Pg.141]


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See also in sourсe #XX -- [ Pg.294 ]




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Acidic phenols

Acidic resin

Formaldehyde resin

Formaldehyde, acid catalyzed

Phenol acid-catalyzed

Phenol acidity

Phenol acids

Phenol formaldehyd

Phenol resin

Phenol-Formaldehyde (Phenolics)

Phenol-formaldehyde

Phenol-formaldehyde resin

Phenolic acidity

Phenolic acids

Phenolic resins

Phenolic-formaldehyde resins

Phenolics phenolic acids

Resinic acids

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