What Is Polycarbonate ? The Stuff They Use For The Lenses In Sunglasses, Safety Glasses And Goggles

Polycarbonates are a particular group of thermoplastics. They are easily worked, molded, and thermoformed; as such, these plastics are very widely used in modern manufacturing. They are called polycarbonates because they are polymers having functional groups linked together by carbonate groups (-O-(C=O)-O-) in a long molecular chain. Also carbon monoxide was used as a C1-synthon on an industrial scale to produce diphenyl carbonate, being later trans-esterificated with a diphenolic derivative affording poly(aromatic carbonate)s. Taking into consideration the C1-synthon we can divide polycarbonates into poly(aromatic carbonate)s and poly(aliphatic carbonate)s. The second one, poly(aliphatic carbonate)s are a product of the reaction of carbon dioxide with epoxides, what owing to the thermodynamical stability of carbon dioxide requires the use of catalyst. The working systems are based on porphyrins, alkoxides, carboxylates, salens and beta-diiminates as organic, chelating ligands and aluminium, zinc, cobalt and chromium as the metal centres. Poly(aliphatic carbonate)s display promising characteristics, have a better biodegradability than the aromatic ones and could be employed to develop other specialty polymers.

The most common type of polycarbonate plastic is one made from Bisphenol A, in which groups from Bisphenol A are linked together by carbonate groups in a polymer chain. This polycarbonate is a very durable material, and can be laminated to make bullet-proof "glass", though “bullet-resistant” would be more accurate. The characteristics of polycarbonate are quite like those of polymethyl methacrylate (PMMA; acrylic), but polycarbonate is stronger and more expensive. This polymer is highly transparent to visible light and has better light transmission characteristics than many kinds of glass. CR-39 is a specific polycarbonate material with good optical and mechanical properties, frequently used for eyeglass lenses.

Polycarbonate has :

a density of 1.20 g/cm3
a use range from -100°C to +135°C
a melting point around 250°C
a refractive index equal to 1.585 ± 0.001
a light transmission index equal to 90% ± 1%
poor weathering in an ultraviolet (UV) light environment
Polycarbonate is becoming more common in housewares as well as laboratories and in industry. It is often used to create protective features, for example in banks as well as vandal-proof windows and lighting lenses for many buildings. Other products made from polycarbonate include sunglass/eyeglass lenses, compact discs, DVDs, and automotive headlamp lenses. It is the major component of one variety of Nalgene bottles. It is also used for animal enclosures and cages used in research.

LEXAN® is the registered trademark for polycarbonate plastic manufactured (from Bisphenol A) by General Electric. MERLON® is the registered trademark used by the Mobay Chemical Company. MAKROLON® is the registered trademark for polycarbonate from Bayer, which is also referred to as "macrolon". PANLITE® is the registered trademark for polycarbonate plastic manufactured from Teijin Chemical Limited, which is also the major producer for optical grade polycarbonate.

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