r
T H E epoxy resin development is probably at its most exciting stage of progress-that stage at which new types of materials, new techniques of formulation, and new applications are coming at such a rate as to make the results of surveys obsolete by the time they are completed. Although Wurtz had, in 1860, demonstrated that ethylene oxide, the simplest epoxide, would readily polymerize, it was not until around 1940 that this chemical group’s value in synthesizing water-insensitive materials was recognized. The resinous expoxides, prepared from epichlorohydrin and bis- (4-hydroxy phenyl)dimethylmethane (bisphenol A), represent the bulk of the commercially used epoxy resins. These bisphenol A compositions are, however, being rapidly supplemented with both resinous and nonresinous polyepoxides, including a great variety of materials made by epoxidation of olefin compounds. One of the early applications which is today consuming a large portion of the epoxy resins is esterification with unsaturated vegetable oil acids to give varnishes which are well known for flexibility, light color, alkali resistance, and abrasion resistance. The epoxy resins also form infusible, insoluble products by direct polymerization in the presence of catalysts or by reaction with compounds containing a plurality of active hydrogen groups attached to oxygen, nitrogen, or sulfur. While some of these reactions are carried out at high temperatures, many of the formulated products
convert to infusible materials by reaction at room temperatures. Because of a n outstanding combination of physical properties-excellent adhesion to many surfaces, good electrical properties, low contraction on curing, extreme hardness yet good flexibility, and outstanding alkali and solvent resistance-the epoxy resins are enjoying greater commercial success than could have been anticipated in the early 1940’s. Commercialization, starting around 1950, reached a n annual production of 30,000,000 to 35,000,000 pounds in 1956, a n increase of better than 10,000,000 pounds over 1955. Commercial producers are now talking in terms of topping 100,000,000 pounds annual production by around 1960. These figures do not include epoxidized vegetable oil plasticizers. As indicated by their many applications in protective coatings, adhesives, electrical embedding, tool, die and patterns, and glass fiber-reinforced structural materials, there appears to be a never-ending list of new products made possible by the versatility of this new family of resins. The outlook for commercial exploitation of the epoxy resins is based not alone on existing types. There is much research in progress to develop new types and modifications. A bridge is rapidly taking form between the epoxy resins and the epoxidized vegetable oil plasticizers. There is now considerable physical chemical research in progress, which should also broaden application through a better theoretical understanding of these materials. S. 0. GREENLEE VOL. 49, NO. 7
JULY 1957
1079
