Acetylene, when passed into a solution of copper chloride and ammonium chloride, combines with itself. When two molecules of acetylene react monovinyl acetylene is formed, and when three molecules of acetylene react divinyl acetylene is formed. Monovinyl acetylene reacts with hydrochloric acid to give chloroprene, which is polymerized to synthetic rubber or Neoprene.
Divinyl acetylene is a colorless liquid which darkens on exposure to light and which has an onionlike odor. When polymerized liquids are formed, then as the reaction progresses viscous products and finally insoluble, infusible, inert resins. By arresting the reaction before the gel point is reached, an amber colored heavy liquid, soluble in aromatic hydrocarbons, is obtained. Since divinyl acetylene will continue to polymerize at ordinary temperatures, this property is taken advantage of in using it as a basis for paints, under the name “synthetic drying oil.” Clear, amber films are obtained from solutions of this oil in solvent naphtha. Divinyl acetylene is quick drying, is many times more impervious to moisture than linseed oil, and is thermosetting. It is not attacked by solvents but is attacked by strong oxidizing agents, and the gelled material may ignite spontaneously.
Although not classified as a resin, synthetic rubber is discussed here because of its close chemical relationship to the vinyl resins. It is made commercially by E. I. du Pont de Nemours & Co., Wilmington, Del., and is marketed as Neoprene. It is sold as a plastic polymer which is vulcanized and processed much the same as natural rubber except that sulphur is not essential to vulcanization. Synthetic rubber is higher in price than natural rubber, but it has certain properties which make it suitable for service conditions where natural rubber is unsatisfactory. Among these properties are its resistance to gasoline, oils, and greases, and to elevated temperatures. It does not check or crack on exposure to sunlight, nor does it oxidize as rapidly as natural rubber. Its principal applications are in special gaskets, printing rolls, jackets for high tension cable, linings for gasoline or oil hose lines, balloon fabrics, diaphragms for regulators, and packing for compressors. Its existence acts as a limit to the increase in the price of natural rubber and assures a supply in emergencies.
Production in the United States.
Some of the products described are commercially produced in the United States; others in Canada or in Germany. Those made in the United States are usually not made by more than one firm, so that statistics of production and sales are not publishable. The vinyl acetate resins have been produced principally in Canada; the copolymers of vinyl chloride and vinyl acetate are domestic products. In 1935 the United States output of all vinyl resins exceeded 1,000,000 pounds, a figure that was increased in 1936 and 1937.
The Canadian output of Gelva and Alvar has reached commercial quantities; that of Formvar is still confined to experimental plant lots.
The acceptance of vinyl resin sheets for safety glass will greatly increase the output in 1938. The basic patent, known as the Morrison-Blaike patent, United States No. 2,036,092 issued on March 31, 1936, is owned by Shawinigan Chemicals, Ltd., Montreal, Canada, who have licensed several domestic producers. The monomer (vinyl acetate) is now produced at Niagara Falls, N. Y., by the Niacet Chemicals Corp., which is jointly owned by this Canadian firm, Carbide and Carbon Chemicals Corporation, and E. I. du Pont de Nemours & Co. It is also produced by du Pont at Belle, W. Va. It is shipped, in tank cars, to polymerization and sheet-forming plants at Indian Orchard, Mass., Arlington, N. J., and Charleston, W. Va. The Indian Orchard plant, known as the Shawinigan Resin Products Co., and jointly owned by the Canadian firm and the Fiberloid Corporation, is now in operation. The plant of the du Pont Company at Arlington, N. J., began production in May 1938, and that of Carbide and Carbon Chemicals Corp, at Charleston, W. Va., is in production. These plants have a combined annual capacity of about 10 million pounds of vinyl resin sheets. According to present plans this new safety glass will be available for 1939 model automobiles. The resin sheet to be used is 0.0015 inch thick as compared with the 0.0025 inch thickness of the present cellulose acetate and nitrocellulose sheet. Several trade names have been adopted for the vinyl resin sheets, among which are Vinylite X, and Butvar. The licenses granted to domestic makers under the Morrison-Blaike patent also permit them to make vinyl acetate resins for purposes other than safety-glass sheets. Considerable progress has been made in adapting these resins to injection molding operations for the production of tooth-brush handles, combs, closures, and other parts.
Imports into the United States.
The official statistics of imports of vinyl resins prior to 1936 are not satisfactory for purposes of comparison. Imports could be entered under either paragraph 2 or paragraph 11 and could be included either with the statistics of imports of vinyl acetate (see table [91], page [141]) or be thrown into a general group of non-coal-tar synthetic gums and resins, n. s. p. f., which in addition to vinyl resins would include the acrylates and ureas. Table [10] gives imports of synthetic resins under paragraph 11 of the Tariff Act of 1930.