Polycarbonate

A polycarbonate is a synthetic thermoplastic compound used as a durable, lightweight alternative to glass. A thermoplastic is a plastic that melts and becomes pliable at a specific temperature, and it solidifies upon cooling, thus retaining its shape. While polycarbonate was first discovered in the late nineteenth century, it was more than half a century later that the compound was able to be used in practical applications. Its impact-resistant and transparent properties allow it to be used in a variety of common products, such as eyeglass lenses, bulletproof or shatter-resistant plastic, and compact discs and DVDs.

Overview

A polycarbonate is a chemical compound known as a polymer, a substance created by the combination of smaller molecules into a chainlike network. It is produced by a chemical reaction involving an organic compound called bisphenol A and phosgene gas, made by combining carbon monoxide with chlorine. The chemical formula for the repeating unit of polycarbonate is C₁₆H₁₄O₃, meaning its structure contains sixteen carbon atoms, fourteen hydrogen atoms, and three oxygen atoms per monomer unit. This structure contains molecular groups such as phenyl and methyl groups. Phenyl groups are molecules with six carbon and five hydrogen atoms (C₆H₅), and methyl groups contain one carbon and three hydrogen atoms (CH₃). Phenyl groups have a high degree of attraction to other substances and combine easily with methyl groups. This process leads to a lack of mobility in the individual molecules, resulting in a substance that can be easily melted and molded. It also allows polycarbonates to maintain their shape without crystallization when cooled, meaning the substances remain transparent.

Polycarbonate was first synthesized in 1898 by German chemist Alfred Einhorn. Scientists, however, were unable to discover any commercial use for the substance and research on it was abandoned. In 1953, two scientists, working independently, rediscovered polycarbonate within weeks of each other. Hermann Schnell, working for the German chemical and pharmaceutical company Bayer AG, and Daniel W. Fox, with the General Electric Company in the United States, are credited with the discovery. Bayer trademarked its substance under the name Makrolon, and General Electric used the name Lexan. Initially, polycarbonate was used in electrical and electronic products such as fuse boxes and plugs, and as a coating for greenhouse windows and public buildings.

By the 1970s and 1980s, polycarbonate’s durable, yet transparent, properties allowed it to be used in a variety of applications. Automobile manufacturers used it as a covering for headlights and taillights. It was used to make shatterproof bottles and food containers that could withstand freezing or reheating in microwaves. Polycarbonate were also used in the creation of compact discs and DVDs for music and other media, and as coverings for cell phones and computer tablets. One of the most common applications of polycarbonate is in optical lenses for eyeglasses. The substance’s light weight, shatter resistance, and ease at which it can be made to fit eyeglass rims makes it far superior to glass lenses. It can also be modified to block ultraviolet rays while maintaining its optical quality.

Bibliography

Bendler, John T., and Donald G. LeGrand, editors. Handbook of Polycarbonate Science and Technology. Marcel Dekker, 2000.

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