Abstract: A resinous linear polyester, poly(oxy-1,4-phenylene-3-oxotrimethylene), is made by the self-condensation of 3-(parahydroxyphenyl)propionic acid. The process is carried out interfacially or in an inert solvent by mixing 3-(parahydroxyphenyl)propionic acid with at least an equimolar proportion of thionyl chloride and maintaining the mixture at a reaction temperature for a time sufficient to allow substantially complete autocondensation. A base may be added in proportion at least about equivalent to the thionyl chloride. The autocondensate when purified is a white solid linear polyester not melting up to 360.degree. C. and may exhibit an intrinsic viscosity of at least 75 ml/g. It may be molded or pressed into a film.Co-condensed polyesters of 3-(parahydroxyphenyl)propionic acid with up to an equimolar proportion of parahydroxyphenylacetic acid may similarly be prepared.