Fiber and film-forming polycondensates

Fibre- and film-forming polymeric linear aromatic anhydrides with recurring units of the formula where the carbonyl groups are either both in the para- or both in the meta-position and R represents -O-, -CH2-, are prepared by heating mixed anhydrides of acetic acid or an aliphatic carboxylic acid which has a boiling point between 140 DEG and 250 DEG C. with a dicarboxylic acid of the above unit formula until a fibre- and film-forming polymer is obtained, the monocarboxylic acid and anhydride being distilled off in the process (for preparation of the mixed anhydrides see Group IV (b)). The process is preferably carried out at first at atmospheric pressure and later at reduced pressure. Three types of process are discussed, only the first being exemplified: (i) the reaction mass is maintained in the molten state and is mixed either by bubbling a stream of nitrogen through the mass or by mechanical agitation; (ii) the reaction mass is in powder form and is maintained at a temperature just below the melting point and preferably under high vacuum; or (iii) the reaction may be carried out in an inert high boiling solvent for the polymer such as a -methyl naphthalene, diphenyl or diphenyloxide. The polymer is also soluble in isophorone, m-cresol, phenol and tetrachlorethane. The polymer may be colddrawn or extruded. In the second Provisional Specification, R is a divalent hydrocarbon radical wherein one or more non-adjacent C atoms may or may not be replaced by an ether-oxygen atom, this divalent radical uniting the two benzoyl radicals with 1-8 atoms in the aliphatic or alicyclic chain. Many such are specified. Further the carbonyl groups in the formula may be mixed meta- and para-.ALSO:The invention comprises mixed anhydrides of an aromatic dicarboxylic acid, of the general formula wherein the carbonyl groups are either both in the meta- or both in the para-position, R1 is an aliphatic acyl radical derived from a monocarboxylic acid with a boiling point between 140 DEG and 250 DEG C., R11 is the same as R1 or hydrogen, and R is -O-, -CH2, They may be prepared by heating the dicarboxylic acid in the presence of excess acetic anhydride (the only mono carboxylic compound disclosed) at a temperature sufficiently high to cause distillation of both acetic acid and acetic anhydride. When the reaction is completed, the mixed anhydride separates out, on being cooled, as a crystal