Bakelite synthesis

Condensation polymers. A. Polyester/polyamide/polyimide formation by combining A2 and 82 monomers or from a single AB monomer. Several common polymers of this class are shown. B. The diisocyanate route to polyurethanes and polyureas. C. Bakelite synthesis. Note that the final product is heavily cross-linked because of the presence of bis and tris adducts in the initial reaction with formaldehyde. 

Frederick Frey and Walter Shultze were instrumental early researchers. Frey was among the first to dehydrogenate paraffins catalytically to olefins and then the olefins to diolefins that serve as feedstocks to the production of many of today s polymers. In competition with Bakelite, he discovered the preparation of polysulfone polymers made from the reaction of sulfur dioxide and olefins creating a hard Bakelite-like material. Frey and Schultz also developed a process that allowed the production of 1,3-butadiene from butane that allowed the synthesis of SR. 

All of these inventions utilized natural materials at least as one ingredient. After years of work in his chemistry labs in Yonkers, New York, Leo Baekeland in 1907 announced in an American Chemical Society meeting the synthesis of the first truly synthetic polymeric material, later dubbed Bakelite. 

The first synthetic polymers to be of any use were the phenol formaldehyde resins of which the most famous, Bakelite, was discovered by Bakeland at the turn of the century. He combined phenol and formaldehyde in acid solution and got a reaction that starts like the bisphenol A synthesis. 

In the experiments that follow, you will find that the preparation of nylon by interfacial polymerization is a spectacular and reliable experiment easily carried out in one afternoon. The synthesis of Bakelite works well it requires overnight heating in an oven to complete the polymerization. Nylon by ring-opening polymerization requires skill and care because of the high temperatures involved. The polymerization of styrene also requires care, but is somewhat easier to carry out. 

In the final step in the synthesis of Bakelite the partially polymerized material is heated at 85°C for several hours. What other product is produced in this reaction ... 

Make sure that you can drawthe mechanism forthis reaction—two electrophilic aromatic substitutions are involved (Chapter 22). If you need a hint look at the synthesis of Bakelite on the next page. 

Benzene and toluene are excellent laboratory and industrial solvents. In addition, they are the starting materials for the synthesis of hundreds of other valuable aromatic compounds that are intermediates in the manufacture of a wide variety of commercial products, including the important polymers Bakelite and polystyrene (see > Table 2.4). 

Formaldehyde, HCHO, is an economically important aldehyde. It s used as a solvent and for preservation of biological specimens. Formaldehyde is also used in the synthesis of certain polymers, such as Bakelite and Melmac (used in melamine dishes). Other aldehydes, especially those with a benzene ring in their structure, have pleasing odors and, like esters, are used in the perfume and flavoring industry. 

Bakelite Bakelite is the first tradename for the phenol formaldehyde resin. This was the first commercial polymer. Bakelite was designated after its inventor Leo Hendrick Baekeland (1863-1944), a Belgian who did the work on the synthesis of phenolic resins and their commercial development in the early 1900s. 

The resorcinol-formaldehyde polymer is classified as a phenolic resin. In fact, phenol-formaldehyde condensates are the first synthetic polymers introduced commercially (Bakelite) in the beginning of the twentieth century. Thus, the phenolic resin chemistry, on which there is a vast amotmt of information, can be used to understand the chemistry of the RF aerogel synthesis. In the first step, resorcinol reacts with formaldehyde to form hydro-xymethylated resorcinol in the second step, the hydroxymethyl groups condense with each other to form nanometer-sized clusters, which then crosslink by the same chemistry to produce a gel. The formation of clusters is influenced by typical sol-gel parameters such as the temperature, pH, and concentration of reactants. Though the first RF aerogel is synthesized by the aqueous polycondensation of resorcinol with formaldehyde with the use of sodium carbonate as catalyst [6, 12, 13], now several literature reports exist for aerogels made from phenol and formaldehyde [14—16]. 

Cross-linked pol)uners are formed when long chains are linked in one gigantic, three-dimensional structure with tremendous rigidity. Addition and condensation polymers can exist with a cross-linked network, depending on the monomers used in the synthesis. Familiar examples of cross-linked polymers are Bakelite, rubber, and casting (boat) resin. The process can be represented as follows ... 

Calixarenes are the products of condensation of p-alkyl-phenols and formaldehyde, which is the main route for the synthesis of these compounds. These starting materials are those used for production of bakelite, and indeed calixarenes were first made during a study of the formation of this material [28, 29]. The product isolated was assumed to be exclusively calix[4]arene. Later, after numerous studies, it was found that a mixture of calixarenes is actually formed on reaction of the corresponding ligsons, and the precise course of the reaction depends on many factors [26, 27, 30-33]. The basic variables relevant to the one-flask process in the presence of bases are as follows ... 

The calixarenes (from the Greek calix, meaning chalice) are a family of structures that have seen extensive use in many contexts. Shown below is the remarkable, one-step synthesis of the prototype calixarene. This condensation reaction is a variant of the phenol-aldehyde condensation that produces bakelite, the first synthetic polymer. Early workers spent considerable effort to optimize this synthesis, biasing the product toward the calixarene... 

Bakelite was a thermoset that is, it did not flow after the synthesis was complete (20). The first synthetic thermoplastics, materials that could flow on heating, were poly(vinyl chloride), poly(styrene-5t t-butadiene), polystyrene, and polyamide 66 see Table 1.8 (20). Other breakthrough polymers have included the very high modulus aromatic polyamides, known as Kevlar (see Section 7.4), and a host of high temperature polymers. 

A by-product of this process is acetone, which is also a commercially important compound. Over two million tons of phenol is produced each year in the United States. Phenol is used as a precursor in the synthesis of a wide variety of pharmaceuticals and other commercially useful compounds, including bakelite (a synthetic polymer made from phenol and formaldehyde), adhesives for plywood, and antioxidant food additives (BHT and BHA, discussed in Chapter 11). 

Condensation polymerization also has a special place in polymer science history. The first truly synthetic polymer, Bakelite, was developed in 1907, as the condensation product of phenol and formaldehyde [66]. Meanwhile, Wallace Carothers pioneered polyester synthesis in the 1930s at Dupont and developed a series of mathematical eqnations to describe the kinetics, stoichiometry, and molecular weight distribution of condensation polymerizations. 

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