Introduction to Polymers

James Richard Fromm

Giant molecules called polymers are made up by the linkage of simpler molecules (monomers) by a polymerization reaction into essentially endless chain structures. Polymers occur naturally, but the majority which are used commercially are manufactured from simple monomers.

The most well known natural polymers are proteins (polymers of amino acids), nucleic acids (polymers of ribose or deoxyribose sugars with attached purine or pyrimidine bases), and the polymers of glucose (starch, glycogen, cellulose). Synthetic polymers were originally derived from these natural polymers. The first commercially successful synthetic polymer was cellulose nitrate (Celluloid, 1869) which was first practically molded as a substitute for ivory in billiard balls. Nitration of cellulose, [C6H7O2(OH)3].xH2O, produces mixtures of cellulose trinitrate, called guncotton, and cellulose dinitrate, called pyroxylin. John Wesley Hyatt discovered that pyroxylin, when mixed with camphor, becomes a thermoplastic, a substance which can be molded when heated. Unfortunately, cellulose nitrate is also an explosive and its use in motion picture film and in billiard balls occasionally produced spectacularly inflammable incidents. Cellulose acetate, discussed in a following section, soon replaced it.

The second development was that of casein-formaldehyde plastics (A. Spitteler, 1899) made using formaldehyde (H2C=O) and casein obtained from milk. These polymers are no longer of industrial significance. Phenol (C6H5OH)-formaldehyde resins (Bakelite, 1909) were developed in the United States by the Belgian-born chemist Leo Baeckeland while searching for a substitute for varnish shellac .Heating these resins under pressure gave soft solids which could be molded and then hardened; they were both safe and economical. These early polymers have now been replaced by others based on simpler monomers.

The polymer industry is normally divided into three areas on the basis of the type of product manufactured: synthetic plastics, man-made textile fibers, and synthetic rubber. Some polymers have properties which permit their use in more than one of these areas.

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Copyright 1997 James R. Fromm