Synthetic polymers phenol-formaldehyde

The history of synthetic polymers is incredibly short. The term polymer was introduced in 1832. The first synthetic polymer (phenol-formaldehyde) was commercialized as Bakelite in 1909, while the first thermoplastic (polystyrene, Trolitul ), 6 years later. The early polymer industry was developed by entrepreneurs that had little if any technical background. The commercial successes (and... 

Baekeland made the first synthetic polymer, phenol formaldehyde resin... 

The first completely synthetic plastic, phenol-formaldehyde, was introduced by L. H. Baekeland in 1909, nearly four decades after J. W. Hyatt had developed a semisynthetic plastic—cellulose nitrate. Both Hyatt and Baekeland invented their plastics by trial and error. Thus the step from the idea of macromolecules to the reality of producing them at will was still not made. It had to wait till the pioneering work of Hermann Staudinger, who, in 1924, proposed linear molecular structures for polystyrene and natural rubber. His work brought recognition to the fact that the macromolecules really are linear polymers. After this it did not take long for other materials to arrive. In 1927 poly(vinyl chloride) (PVC) and cellulose acetate were developed, and 1929 saw the introduction of urea-formaldehyde (UF) resins. 

In practice, synthetic polymers are sometimes divided into two classes, thermosetting and thermo-plMtic. Those polymers which in their original condition will fiow and can be moulded by heat and pressime, but which in their finished or cured state cannot be re softened or moulded are known as thermo setting (examples phenol formaldehyde or urea formaldehyde polymer). Thermoplastic polymers can be resoftened and remoulded by heat (examples ethylene polymers and polymers of acrylic esters). 

The first cellular synthetic plastic was an unwanted cellular phenol—formaldehyde resin produced by early workers in this field. The elimination of cell formation in these resins, as given by Baekeland in his 1909 heat and pressure patent (2), is generally considered the birth of the plastics industry. The first commercial cellular polymer was sponge mbber, introduced between 1910 and 1920 (3). 

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. 

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. 

The first widely used synthetic polymer was phenol formaldehyde (Bakelite). It is made by heating phenol (C6H5OH—hydroxybenzene) together with formalde-hyde (H2CO).These react to yield a three-dimensionally cross-linked polymer. To reduce the brittleness of Bakelite, it is usually filled with fibers or platelets of an inert solid. It is a good electrical insulator, relatively hard, and thermally stable to a few hundred degrees Centigrade. Its hardness is 50-60 kg/ mm2 (Mott, 1956). 

In general, the acid-sorbing resins may be classified as high molecular weight polyamines or polyimines. Thus, the original Adams and Holmes material was a polymer of m-phenylenediamine. Cation Exchange materials include synthetic resins, such as sulfonated phenol-formaldehyde or polystyrene types, and sulfonated coal. Some manufacturers have a variety of sub-types which are considered superior for particular applications. 

True synthetic polymers came into use when Bakeland came from Belgium and applied his knowledge of the formation of a moldable plastic from phenol and formaldehyde to give the product named Bakelite. This was about 1914. This product, under heat and pressure, set up to a thermo-setting resin and had useful properties especially as an insulating material for electrical items. 

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. 

While condensation polymers account for only a modest fraction of all synthetic polymers, most natural polymers are of the condensation type. The first all-synthetic polymer, Bakelite, was produced by the stepwise polycondensation of phenol and formaldehyde. 

Chen (29) found that the amount of sulfuric acid directly determines the hardening time in the acid condensation of spent sulfite liquors used in plywood and veneers. However, in general the adhesives based purely on acid condensed lignins have often been found to be an uneconomic and qualitatively inferior alternative to adhesives based on synthetic polymers and phenol or lignin-formaldehyde resins. 

By 1924 Bakelite had become so popular that it was featured on the cover of Time magazine as a substance that will not burn and will not melt. Bakelite jewelry, telephones, pens, radios, car parts, airplane propellers, ashtrays, billiard balls, and cameras were everywhere. Just about the only item that did not become popular was the Bakelite coffin. People would wear, cook in, and eat off plastic, but they refused to be buried in it. Bakelite s success stimulated research to improve the material even further, especially after scientists pointed out that in the manufacture of Bakelite the small phenol and formaldehyde molecules had joined together to make a giant three-dimensional lattice. In other words. Bakelite was the world s first synthetic giant molecule, the first synthetic polymer. 

The first synthetic plastics were the phenol-formaldehyde resins introduced by Baekeland in 1907 [1], Melamine and urea also react with formaldehyde to form intermediate methylol compounds which condense to cross-linked polymers much like phenol-formaldehyde resins. Paper, cotton fabric, wood flour or other forms of cellulose have long been used to reinforce these methylol-functional polymers. Methylol groups react with hydroxyl groups of cellulose to form stable ether linkages to bond filler to polymers. Cellulose is so compatible with these resins that no one thought of an interface between them, and the term reinforced composites was not even used to describe these reinforced systems. 

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 . 

Bakelite, the first synthetic polymer, is an example of a thermoset polymer. It is prepared by the polymerization of phenol and formaldehyde in the presence of ail acid. Carbocations produced by protonation of formaldehyde bond to the ortho and para positions of the highly reactive phenol molecules in a Friedel-Crafts alkylation reaction. The benzylic alcohols that are produced in this step react to produce carbocations that then alkylate additional phenol molecules. A mechanism for the first few steps of this polymerization process is shown in Figure 24.4. 

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. 

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. 

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