Fiber-forming polyesters of aromatic ketohydroxy acids

Claim 1

Fiber-forming melt-spinnable polyester that is optically anisotropic in the melt and consists essentially of the following amounts of recurring units of the structural formulas: (a) 25-100 mol % ##STR5## and (b) 0-75 mol % ##STR6## wherein both of R 1 and R 2 are H, CH 3 or Cl or R 1 is H and R 2 is CH 3 or Cl; both of R 3 and R 4 are H, CH 3 or Cl or R 3 is H and R 4 is CH 3 or Cl; and Ar is m- or p-phenylene, provided, however, when the amount of (a) is 90-100 mol %, Ar is m-phenylene in at least 30% of the (a) units, and provided further, however, when the amount of (a) is 100 mol % and only one species of (a) is present, R 1 and R 2 are both Cl, and provided still further, however, in copolyesters consisting essentially of two or more different species of (a), only one of said species is substituted and R 1 and R 2 therein are Cl.