Process for forming thermally stable thermotropic liquid crystalline polyesters of predetermined chain length utilizing aliphatic dicarboxylic acid

Claim 1

In a process for the formation within a polymerization zone of a polyester which is capable of forming an anisotropic melt phase and which optionally may include amide linkages through a polymerization reaction of ester-forming and optionally also amide-forming monomers to form a polymer having recurring moieties selected from the group consisting of the following where in each instance Ar comprises at least one aromatic ring: (a) ##STR13## (b) --O--Ar--O--, (c) ##STR14## (d) --Y--Ar--Z--, where Y is O, NH, or NR, and Z is NH or NR where R is an alkyl group of 1 to 6 carbon atoms or an aryl group, (e) ##STR15## where Z is NH or NR where R is an alkyl group of 1 to 6 carbon atoms or an aryl group, and (f) fixtures of the foregoing; the improvement of providing in the polymerization zone during said polymerization reaction an approximately 0.25 to 4 percent molar excess of aliphatic dicarboxylic acid monomer containing 4 to 12 carbon atoms and/or an esterified derivative thereof which during the polymerization reaction imparts dicarboxyaliphatic units to the interior of the polymer chains of the resulting polymer and causes the polymer chains to terminate in carboxylic acid end groups and/or an esterified derivative thereof wherein the polymer chains achieve a predetermined average chain length through the depletion of other monomers present in the polymerization zone to yield a polyester product which is substantially incapable of additional chain growth upon subsequent heating.