Quick-crystallizing polyester composition

Quick-crystallizing polyester compositions comprising a mixture consisting essentially of a polyester thermoplastic resin and a preformed nucleating agent selected from the class consisting of polymeric-base salts, or mixtures of salts, of alkali or alkaline-earth metals of the formula:

• M--(OOC--C.sub.6 H.sub.4 --COO--CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2).sub.m (OOC--Z--COOY).sub.n (ABRX) (1)
• wherein
• M is an alkali or an alkaline-earth metal;
• Y is a group selected from:
• --CH.sub.2 CH.sub.2 --, --(CH.sub.2).sub.4 -- or --CH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 --;
• Z is a group --C.sub.6 H.sub.4 --, or a group --(CH.sub.2).sub.q --, q being an integer from 7 to 10;
• A is an anion selected from the group consisting of carboxylate, sulphonate, sulphinate, phosphonate and phosphinate;
• B is a direct bond or a group selected from the class consisting of --CH.dbd.CH--, --CH.sub.2 -- and --CH.sub.2 CH.sub.2 --;
• R is an arylene radical containing from 1 to 3 aromatic rings directly linked with one another or condensed or bound by means of one of the following difunctional groups;
• --O--, --CO--, --OCH.sub.2 CH.sub.2 O--, --SO.sub.2 --, --NH--, --C(CH.sub.3).sub.2 --, or R is a thiophene or furane ring and, when A is a carboxylate and B is a direct bond, R may carry as a substituent at least one nitro, halogen, phenyl or oxyphenyl group;
• X is a hydrogen atom or, when A is a carboxylate, B is a direct bond and R a substituted or unsubstituted phenyl ring, X is a --COOM group or a --COO(CH.sub.2).sub.4 OH group;
• m is an integer from 5 to 20;
• and
• n is 0 or an integer from 1 to 5 said compositions being devoid of monomeric alkali or alkaline-earth terephthalates.