Polyesters of polymeric fatty acids with ethylene glycol may be compounded and cured with sulfur and other conventional reagents to yield a vulcanízate having improved properties as compared with factice. When special effort is made to complete the polyesterification reaction, further improvement in the vulcanízate is achieved. Soybean, linseed, and tall oils are possible raw material sources for this rubber substitute.Evaluation tests indicate that it can be calendered onto cloth, that it has good resistance to oxygen and ozone, and that it has sufficient tackiness for use as an adhesive.THE high price and shortage of natural rubber during certain periods in the last forty years have led to a large number of investigations to find substitutes for the product of the Hevea tree. One phase of investigation has been the attempt to modify vegetable oils by polymerization, sulfurization, and oxidation.A large number of experimental variables, such as catalyst, sulturizing agents, and compounding agents, were studied in an endeavor to improve the basic discovery that vegetable oils will give rubbery products, and a review of the literature was given (15). These studies showed that products possessing high tensile strength but low elasticity could be achieved. All attempts to achieve high elasticity with good tensile characteristics failed. Many research developments in the chemistry of polymeric materials served to emphasize that one requisite of elastomers is that they be composed of long linear chains. The authors believed that if the functionality of a vegetable oil or oil derivative was correctly controlled, a product would be obtained superior in tensile strength and elasticity to any previously known rubberlike materials made from vegetable oils. An investigation of a number of oil derivatives led to a vulcanized polyester of polymeric fatty acids and ethylene glycol. If the polyesterification were carried to a sufficient degree, no special procedures were required to give a vulcanized product. It was necessary to increase the viscosity of polyesters of relatively low molecular weight by heating in air and to give the compounded polyester a precure.The vulcanized product had sufficient strength and elasticity so that its production and use on a large scale was investigated by industrial concerns. THEORETICAL Carothers (5) discussed the possibility that one structural requisite of rubberlike molecules may be long linear chains, and Bradley (2) published some excellent papers and gave other references on the relation of functionality to the polymerization of oils.Our discussion on these two subjects will be limited to the possible production of rubberlike materials from vegetable oils. 1 Northern Regional Polymer. Some of the information contained in this paper was submitted for publication to the director of the Northern Regional Research Laboratory in June, 1942. Publication was stopped by issuance of a secrecy order by the Patent Office, dated July 9, 1942, on a patent application of Cowan and Ault entitled "Pro...