Formaldehyde-phenol polymers

Phenol-formaldehyde polymers are polymers formed by the interaction of a phenol, or a mixture of phenols, and formaldehyde. Commercial materials are most commonly based on phenol itself other phenols such as cresols, xylenols and resorcinol are used to a limited extent. It may be noted that several aldehydes other than formaldehyde have been used to prepare phenolic polymers but none has attained appreciable commercial significance. 

Phenol-formaldehyde polymers are also of significance in that they were the first wholly synthetic polymers to be utilized. They were truly man-made, being prepared from low molecular weight reagents. Prior to this time, the only polymers available were those based on naturally occurring polymers. 

Phenol occurs in coal tar and at one time this source satisfied commercial demands. Nowadays, however, natural phenol accounts for very little of the total world production of phenol the majority is synthesized from benzene. Since benzene (which also occurs in coal tar) is now extensively obtained from petroleum sources, phenol may be counted as a major petroleum chemical. A number of processes for the manufacture of phenol have been operated over the years but now the cumene process accounts for at least 90% of the current output of phenol and only this process is described in this section. The method proceeds from benzene as follows  

In the first step, benzene is alkylated with propylene to give isopropyl benzene (cumene). The reaction may be carried out in either the vapour or liquid phase. In the vapour phase process (which is more common), propylene and an excess of benzene are passed over a catalyst of phosphoric acid supported on kieselguhr at about 250°C and 2.5 MPa (25 atmospheres). The exit gases are fractionated cumene is taken off and unreacted benzene is 

In the third step in the synthesis of phenol, the cumene hydroperoxide undergoes cleavage to phenol and acetone. This is usually accomplished by feeding the hydroperoxide, with sulphuric acid as catalyst, continuously into previously decomposed material maintained at about 50-90°C. The product is then neutralized and fractionated by distillation. The cleavage reaction proceeds as follows  

This method proceeds from benzene as follows  

These are thermoset polymers made from phenol or, less commonly, phenolic-type compounds such as the cresols, xylenols, and resorcinol, together with formaldehyde. They had been known for some time - G.T (later Sir Gilbert) Morgan discovered them in the early 1890s when attempting (unsuccessfully) to make artificial dyestuffs by reaction of phenol with formaldehyde. But this knowledge had not been exploited before 1907, the year in which Leo 

Baekeland in America obtained his first patent for materials prepared from these two compounds. In 1910 he founded the General Bakelite Company to exploit this development, in the process making phenol-formaldehydes, the first synthetic polymers to achieve commercial importance. 

Baekeland had to make important discoveries before he could bridge the gap between the initial concept and final products. In particular, he found that the base-catalysed condensation of phenol and formaldehyde can be carried out in two parts. If the process is carefully controlled, an intermediate product can be isolated, either as a liquid or a solid, depending on the extent of reaction. At this stage, the material consists of essentially linear molecules and is both fusible and soluble in appropriate solvents. When heated under pressure to 150 °C, this intermediate is converted to the hard, infusible solid known as bakelite . This second stage is the one at which the three-dimensional cross-linked network develops. 

Phenol-formaldehydes may no longer hold the centre-stage where synthetic polymers are concerned, but they are still of some commercial importance. They are produced for electrical mouldings, appliance handles, household fittings, and also as adhesives and specialised surface coatings. 

Cured phenol-formaldehydes are resistant to attack by most chemicals. Organic solvents and water have no effect on them, though they will swell in boiling phenols. Simple resins are readily attacked by sodium hydroxide solutions, but resins based on phenol derivatives, such as cresol, tend to be less affected by such solutions. Simple phenol-formaldehyde polymers are resistant to most acids, though formic and nitric acids will tend to attack them. Again, cresol-based polymers have resistance to such attack. 

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Polymers. Quinoline and its derivatives may be added to or incorporated in polymers to introduce ion-exchange properties (see Ion exchange). For example, phenol—formaldehyde polymers have been treated with quinoline, quinaldine, or lepidine (81) (see Phenolic resins). Resins with variable basic exchange capacities have been prepared by treating Amherlites with 2-methylquinoline (82). 

Unlike phenol-formaldehyde polymers, the amino resins are not themselves deeply coloured, but are of a naturally light appearance. They can be easily pigmented to give a variety of shades, which leads to application in uses where good appearance is highly valued, for example in decorative tableware, laminated resins for furniture, and modem white electrical plugs and sockets. 

If the polymer is hard, insoluble, and infusible without decomposition, and if it refuses to swell greatly in any solvent, it may be assumed either that it is highly crystalline, with a melting point above its decomposition temperature, or that it possesses a closely interconnected network structure (e.g., as in a highly reacted glyceryl phthalate or a phenol-formaldehyde polymer). Differentiation between these possibilities is feasible on the basis of X-ray diffraction. 

Phenol-formaldehyde polymer modified with ethylene carbonate WiO [1680]... 

BF3.OH2).217 The use of a sulfonated phenol-formaldehyde polymer in conjunction with formic acid is also reported.208 Acids that are ineffective include phosphoric,208 trichloroacetic, dichloroacetic, and acetic acids.134 It is reported that addition of lithium perchlorate to the reaction mixture improves product... 

Phenol - formaldehyde polymer akelite and related polymers)... 

Phenol - formaldehyde polymers are the oldest synthetic polymers. These are obtained by the condensation reaction of phenol with formaldehyde in the presence of either an acid or a base catalyst. The reaction starts with the initial formation of o-and/or p-hydroxymethylphenol derivatives, which further react with phenol to form compounds having rings joined to each other through -CH2 groups. The initial product could be a linear product - Novolac used in paints. 

Table 11.2 outlines the uses of phenol. We will consider the details of phenol uses in later chapters. Phenol-formaldehyde polymers (phenolics) have a primary use as the adhesive in plywood formulations. We have already studied the synthesis of bisphenol A from phenol and acetone. Phenol s use in detergent synthesis to make alkylphenols will be discussed later. Caprolactam and aniline are mentioned in the following sections in this chapter. 

It should not be taken for granted that all polymers that are defined as condensation polymers by Carothers classification will also be so defined by a consideration of the polymer chain structure. Some condensation polymers do not contain functional groups such as ester or amide in the polymer chain. An example is the phenol-formaldehyde polymers produced by the reaction of phenol (or substituted phenols) with formaldehyde... 

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. 

In Figure 11-10 is shown the flow sheet of an integrated process to produce polymethylmethacrylate (PMMA) and phenol-formaldehyde polymers simultaneously, starting with methane, propane, and cyclohexane. 

Figure 1.14. Portion of a cross-linked phenol-formaldehyde polymer.

Further materials that have been evaluated as supports for solid-phase synthesis include phenol-formaldehyde polymers [239,240], platinum electrodes coated with polythiophenes [241], proteins (bovine serum albumin) [242], polylysine [243], soluble poly (vinyl alcohol) [244], various copolymers of vinyl alcohol [4,245,246], and soluble dendrimers [14,247]. 

BAEKELAND, L. EL (1863-1944). Born in Ghent, Belgium. He did early research in photographic chemistry and invented Velox paper (1893). After working for several years in electrolytic research, he under took fundamental study of the reaction products of phenol and formaldehyde, which culminated in his discovery in 1907 of phenol-formaldehyde polymers originally called Bakelite. The reaction itself had been investigated by Bayer in 1872, but Baekeland was the first to learn how to contiol it to yield dependable results on a commercial scale, The Bakelite Co, (now a division of Union Carbide) was founded in 1910. 

Let us apply Eq. (3.86) to phenol - formaldehyde polymers synthesized in an acid medium with a phenol excess (novolacs). Phenol is a trifunctional reactant (A3), the functional groups being the aromatic hydrogens located in positions 2, 4, and 6 of the phenolic ring. Formaldehyde acts as a bifunctional monomer (B2), forming methylene bridges between the reactive positions of phenol. Novolacs are synthesized with a phenol excess, such that gelation does not occur at full formaldehyde conversion. From Eqs (3.83) and (3.86), we obtain... 

Write a mechanism for a step-growth polymerization, as in the formation of a polyester, polyamide, polyurethane, epoxy resin of phenol-formaldehyde polymer. 

Phenolic resins (phenol-formaldehyde polymers), copolymers of phenol and formaldehyde, were the first fully synthetic polymers made. They were discovered in 1910 by Leo Baekeland and given the trade name Bakelite . 

Of all organic polymers used to produce insulation materials, glyptal and phenol-formaldehyde polymers are the most thermal resistant. They can function for a long time in electrotechnical devices at temperatures up to 130 °C. At higher temperatures insulation from organic polymers bums. Its dielectric properties considerably decrease, because the carbon formed is a good conductor. 

Thermoset resins covers an extremely wide range, including phenol formaldehyde polymers, aminopolymers, PUs, epoxies, and thermoset polyesters, which include the alkyd and unsaturated vinyl ester resins. Of special interest at the present time are those that comprise the resin component of liber-reinforced composites that are finding increasing use in commercial and defense sectors, where fire resistance is of paramount importance. Typical resins used are those listed in Table 2.4 along with typical, respective LOI values in descending order of increased inherent fire resistance. 

Probably the most widely used of these is glassy carbon, which is isotropic. However, due to its hardness and fragility, electrode fabrication is difficult, which essentially limits its use to the dimensions and forms that can be acquired commercially. The manufacture of glassy carbon consists in carbonization by heating phenol/formaldehyde polymers or polyacrylonitrile between 1000°C and 3000°C under pressure. Since glassy carbon has some amorphous characteristics, as can be seen from Fig. 7.1, it is not always homogeneous. 

Articles that are not made from synthetic polymers are often held together or coated with polymers. A bookcase may be made from wood, but the wood is bonded by a phenol-formaldehyde polymer and painted with a latex polymer. Each year, about 400 billion pounds of synthetic organic polymers are produced worldwide, mostly for use in consumer products. Large numbers of organic chemists are employed to develop and produce these polymers. 

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. 

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