Abstract: An aromatic hetero ring-containing polyimide comprising substantially equal equivalent amount of (1) structural units of Group 1 and (2) structural units of Group 2, wherein the structural units of Group 1 comprise (i) from 30 to 100 mol % of a unit of the formula: ##STR1## wherein X is S, O or NH, and (ii) from 0 to 70 mol % of a unit of the formula: ##STR2## wherein Ar.sub.1 is ##STR3## wherein each of y, y.sub.1, and y.sub.2 and y.sub.3 is a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom, and each of Z, Z.sub.1 and Z.sub.2 is a single bond, --O--, --CH.sub.2 --, ##STR4## --C--, --SO.sub.2 --, --C(CH.sub.3).sub.2 -- or --C(CF.sub.3).sub.2, and the structural units of Group 2 comprise (i) from 70 to 100 mol % of a unit of the formula: ##STR5## and (ii) from 0 to 30 mol % of a unit of the formula: ##STR6## wherein Ar.sub.2 is ##STR7## wherein Z, y and y.sub.

Abstract: A polyethylene terephthalate resin composition comprising a polyethylene terephthalate resin and from 0.

Abstract: A polycarbonate containing from 25 to 100% by weight, based on the total carbonate bond-constituting units, of carbonate bond-constituting units each containing at least one pendant aromatic group, and having an average molecular weight of from 9,500 to 14,000.

Abstract: An optical disc substrate made of a polycarbonate containing from 5 to 100% by weight, based on the total carbonate bond-constituting units, of carbonate bond-constituting units having the formula: ##STR1## wherein each of Y and Z is a hydrogen atom or an aliphatic hydrocarbon group having from 1 to 6 carbon atoms, and each of X and W is an aliphatic hydrocarbon group having from 1 to 6 carbon atoms.

Abstract: A thermoplastic resin composition is quickly crystallizable and comprises 0.1 to 10 wt. parts of an alkali metal salt of higher fatty acid having carbon atoms of at least 26 obtained by an addition of a fatty acid to .alpha.-olefin having carbon atoms of at least 23 per 100 wt. parts of a thermoplastic polyester.

Abstract: Polyoxymethylene having high molecular weight and high thermal stability is produced by polymerizing formaldehyde in the presence of a specific catalyst and then heating the resulting polyoxymethylene. The specific catalyst is produced by contacting a phosphorus containing compound or an amine (c) with a reaction product obtained by reacting salicylic acid component (b) with an organoaluminum compound (a) having the formula ##STR1## wherein R.sup.1 represents an alkyl or alkoxyl group and R.sup.2 and R.sup.3 respectively represent alkyl or alkoxyl group or a halogen atom.

Abstract: Polyoxymethylene is produced by polymerizing formaldehyde in the presence of a catalyst comprising a catalytic component of an organoaluminum compound or a complex thereof supported on a modifier of a higher carboxylic acid amide compound.The organoaluminum compound can be in a form of a complex of the organoaluminum compound and a phosphorus compound or an amine.

Abstract: Fibers or films with high mechanical strengths are produced from novolacs which are obtained by reaction of resols with phenols under neutral or acidic conditions.