Abstract: Molding compositions having high rates of crystallization and suitable for being molded at a temperature of the mold not higher than 100.degree. C. to produce molded articles having an optimal combination of mechanical, physical, thermal properties and of surface appearance, comprising: a linear saturated polyester (A); a salt of a mono- or poly-carboxylic acid (B); an ionomer copolymer containing side carboxylic groups at least partially salified (C), and a solid inert inorganic substance (D) having a particle size not higher than 5 micrometers. Said compositions may be reinforced by reinforcing materials, preferably by glass fibers.

Abstract: An oligomer flame-retarding additive can be defined by the general formula ##STR1## wherein: R is the hydrogen atom, or a linear or branched alkyl radical, containing from 1 to 6 carbon atoms;m takes the value 1, 2 or 3;n takes a value, or an average value, comprised within the range of from 2 to 50.Such an additive is obtained by means of the oligomerization of a hydroxyalkylenephenylphosphinic acid or of a related alkyl ester thereof.According to another form of practical embodiment, the flame-retarding additive is the product of co-oligomerization of a hydroxyalkylenephenylphosphinic acid, or of a related alkyl ester thereof, with a phenylphosphonic acid or a related alkyl ester thereof.Such oligomer additives are used for endowing a linear polyester with self-extinguishing characteristics.

Abstract: Process for preparing diesterdiamides, consisting of reacting a diester with a diamine under wet conditions in the presence of suitable solvents and catalysts, to give the diester diamide, together with an ester salt derivative as impurity. The reaction product is then filtered to give a diesterdiamide cake and a mother solution of the reagents which also contains the solvent, the catalyst and the ester salt product. The cake is washed with a solvent of the ester salt, which also dissolves the reagents and catalysts. The mother solution and wash solution are then distilled, the two fractions obtained being recycled to the synthesis and to the wash.

Abstract: A flameproof linear polyester is described containing, copolymerized in the molecule, a phosphorus compound of formula: ##STR1## where R is a hydrogen atom, an alkyl group with 1 to 4 carbon atoms or a hydroxyalkyl group, and R' is a hydrogen atom, a hydroxyalkyl group or the group --(CH.sub.2 CH.sub.2 O).sub.n H, where n varies from 1 to 4. Said linear polyester is prepared by firstly forming a low molecular weight precondensate from a dicarboxylic aromatic acid (or a relative lower alkyl diester) and an alkylene glycol, and then polycondensing in the presence of said phosphorus compound, in such a quantity as to obtain a content of phosphorus (expressed as the metal) in the linear polyester of between 0.4 and 0.8% by weight. The linear polyester thus obtained can be formed into articles such as fibres, film, sheets and other articles which, besides being flameproof, possess improved dyeing characteristics.