be combined with drying o r semi-drying oils for special purposes or used directly in a varnish kettle for producing quickdrying varnishes. Other catalysts, such as sulfuric acid, activated clays, and boron trifluoride, may be employed. The resulting product varies according to the catalyst used. Several companies produce petroleum res ins of these various types and their main outlet is in t h e paint and varnish industry. They are, however, finding uses in other fields, as constituents of printing ink. plastic tile, linoleum, laminates, and im pregnated fibers. The tendency in the past few years has
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been to employ pure or special mixtures of hydrocarbons to produce a certain resin. Ethylene itself can be polymerized under high pressure to produce a rubbery product reportedly having excellent elec trical properties. Another hydrocarbon, isobutylene, when polymerized at sub zero temperatures with boron trifluoride as a catalyst produces a substance very similar in appearance to rubber. Such polymers are added to lubricating oils to improve their viscosity index characteris tics. When isobutylene is copolymerized with a small quantity of a diolefin, a synthetic rubber is produced which may become more important in the very near
future. Styrene itself, which is being manufactured in increasingly large amounts as a constituent for synthetic rubljer, is truly a petroleum resin. Both ethylene and benzene, raw materials for styrene, can be produced from petroleum. Styrene is also found in the distillates when low molecular weight hydrocarbons are pyrolyzed. Resins from petroleum are distinctly an American development. We have a wealth of petroleum and the American chemists and physicists have made good use of this abundance as the starting point for many interesting syntheses—resins from petroleum being one of the many.
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