Polycarbonate: Difference between revisions
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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 disc]]s and [[DVD]]s. It is the major component of one variety of [[Nalgene]] bottles. |
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 disc]]s and [[DVD]]s. It is the major component of one variety of [[Nalgene]] bottles. |
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[[Lexan|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]]. |
[[Lexan|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. |
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==Synthesis== |
==Synthesis== |
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Revision as of 15:19, 13 October 2005
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 monomers groups linked together by carbonate groups (-O-CO-O-) in a long molecular chain.
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.
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%
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 and DVDs. It is the major component of one variety of Nalgene bottles.
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.
Synthesis
Polycarbonate can be synthesized from bisphenol A and phosgene (carbonyl dichloride, COCl2). The first step in the synthesis of polycarbonate from bisphenol A is treatment of bisphenol A with sodium hydroxide. This deprotonates the hydroxyl groups of the bisphenol A molecule.
The deprotonated oxygen reacts with phosgene through a back-side attack to create a tetrahedral intermediate (not shown here) followed by elimination of a chloride ion (Cl-) as a leaving group to form a chloroformate.
The chloroformate is then attacked by another deprotonated bisphenol A, eliminating the remaining chloride ion and forming a dimer of bisphenol A with a carbonate linkage in between.
Repetition of this process yields polycarbonate, a polymer with alternating carbonate groups and groups from bisphenol A. Density starts at about 1.20 g/cm3.