this invention discloses a copolyester which has been found to be optically anisotropic in the melt and which readily undergoes melt processing to form quality fibers and molded articles . these copolyesters are particularly suitable for use in making tire cord which has an outstanding combination of properties including tenacity , modulus , toughness and flex life . this invention specifically reveals a copolyester which is comprised of repeat units which are derived from at least one member selected from the group consisting of phenyl hydroquinone , hydroxy benzoic acid and hydroxy naphthoic acid ; at least one diol selected from the group consisting of 1 , 4 - bis benzene , 1 , 3 - bis benzene , alkyl substituted 1 , 4 - bis benzene , and alkyl substituted 1 , 3 - bis benzene ; and a diacid component which is comprised of terephthalic acid and optionally up to about 10 mole percent isophthalic acid .