CR-39

CR-39, or allyl diglycol carbonate (ADC), is a plastic polymer commonly used in the manufacture of eyeglass lenses. The abbreviation stands for 'Columbia Resin #39', which was the 39th formula of a thermosetting plastic developed by the Columbia Resins project in 1940. CR-39, or allyl diglycol carbonate (ADC), is a plastic polymer commonly used in the manufacture of eyeglass lenses. The abbreviation stands for 'Columbia Resin #39', which was the 39th formula of a thermosetting plastic developed by the Columbia Resins project in 1940. The first commercial use of CR-39 monomer was to help create glass-reinforced plastic fuel tanks for the B-17 bomber aircraft in World War II, reducing weight and increasing range of the bomber. After the War, the Armorlite Lens Company in California is credited with manufacturing the first CR-39 eyeglass lenses in 1947. CR-39 plastic has an index of refraction of 1.498 and an Abbe number of 58. CR-39 is now a trade-marked product of PPG Industries. An alternative use includes a purified version that is used to measure neutron radiation, a type of ionizing radiation, in neutron dosimetry. Although CR-39 is a type of polycarbonate, it should not be confused with the general term polycarbonate, a tough homopolymer usually made from bisphenol A. CR-39 is made by polymerization of diethyleneglycol bis allylcarbonate (ADC) in presence of diisopropyl peroxydicarbonate (IPP) initiator. The presence of the allyl groups allows the polymer to form cross-links; thus, it is a thermoset resin. The monomer structure is