Origins of Polymers:

Polymers have existed in natural form since life began and those such as DNA, RNA, Proteins and polysaccharides play crucial roles in the plant and animal life. From the earliest time, man has exploited naturally occuring polymers as materials for providing clothing, decoration, shelter, tools, weopons, writing materials and other requirements. However, the origins of today's polymer industry commonly are accepted as being in the nineteenth century when important discoveries were made concerning the modification of certain natual polymers.

In 1820 Thomas Hancock discovered that when masticated (i.e. subjected repeatedly to high shear forces), natural rubber becomes more fluid making it easier to blend with additives and to mould. Some years later, in 1839, Charles Goodyear found that the elastic properties of natural rubber could be improved, and its tackiness eliminated, by heating with sulphur. Patents for this discovery were issued in 1844 to goodyear, and slightly earlier to to Hancock, who christened the process vulcanisation. In 1851 Nelson Goodyear, Charles' brother, patented the vulcanisation of natural rubber with large amounts of sulphur to produce a hard material more commonly known as hard rubber, ebonite or vulcanite.

Cellulose nitrate, also called nitrocellulose or gun cotton, first became prominent after Christian Schonbein prepared it in 1846. He was quick to recognise the commercial value of this material as an explosive, and within a year gun cotton was being manufactured. However, more important to the rise of the polymer industry, cellulose nitrate was found to be a hard elastic material which was soluble and could be moulded into different shapes by the applicatio of heat and pressure. Alexander Parkes was the first to take advantage of the combination of properties and in 1862 he exhibited articles made from Parkesine, a form of plasticised cellulose nitrate. In 1870 John and Isaiah Hyatt patented a similar but more easily processed material, named celluloid, which was prepared using camphor as a plasticiser. Unlike Parkesine, celluloid was a great commercial success.

In 1892Charles Cross, Edward Bevan and Clayton Beadle patented the 'viscose process' for dissolving and then regenerating cellulose. The process was first used to produce viscose rayon textile fibres, and subsequently for production of cellophane film.

The polymeric materials described so far are semi-synthetic since they are produced from natural polymers. Leo Baekeland's Bakelite phenol-formaldehyde resins have the destinction of being the first fully synthetic polymers to be commercialised, their production beginning in 1910. The first synthetic rubber to be manufactured, known as methyl rubber, was produced from 2,3-dimethylbutadiene in Germany during Worrld War I as a substitute, although a poor one for natural rubber.

Although the polymer industry was now firmely established, its growth was restricted by the incredible lack of understanding of the nature of polymers. For over a century scientists had been reporting the unusual properties of polymers, and by 1920 the common belief was that they consisted of physically associated aggregates of small molecules. Few scientists gave credence to the viewpoint so passionately believed by Hermann Staudinger, that polymers were composed of very large molecules containing long sequences of simple chemical units linked together by covalent bonds. Staudinger introduced the word 'macro molecule' to descibe polymers, and during the 1920s vigourously set about proving his hypothesis to be correct. Particularly important were his studies on the synthesis, structure and properties of polyoxymethylene and of polystyrene, the results from which left little doubt as to the validity of the macromolecular viewpoint. Straudinger's hypothesis was further substantiated by the crystallographic studies of natural polymers reported by Herman Mark and Kurt Meyer, and by the classic work of Wallace Carothers on the preparation of polyamides and polyesters. Thus by the early 1930's most scientists were convinced of the macromolecular structure of polymers. During the following 20 years, work on polymers increased enormously.

Not surprisingly, as the science of macromolecules emerged, a large number of synthetic polymers went into commercial production for the first time. These include the examples to the left, as well as many others. From the 1950's onwards regular advances, too numerous to mention here, have continued to stimulate both scientific and industrial progress.

Whilst polymer science is now considered to be a mature subject, its breadth is ever increasing and there are many demanding challenges awaiting scientists who venture into this fascinating multidisciplinary science.

Bibliography

Billmeyer, Fred W. Textbook of Polymer Science

Treloar, L R G. Introduction to Polymer Science