Abstract: Polymers having a very good combination of chemical, mechanical and process properties, and particularly useable either alone or as mixtures, as high-tenacity thermoplastic polymer and as elastomers or elastomeric modifiers, contain, randomly distributed along their chain, repeating cycloketonic structural units having the following general formula (I): ##STR1## wherein: A represents a tetravalent aliphatic or cycloaliphatic, substituted or non-substituted moiety containing a total number of from 4 to 50, preferably from 4 to 20, carbon atoms.Such polymers can be prepared by means of a process which comprises reacting, in a liquid media, a polydiene containing adjacent structural units derived from the 1,4-cis polymerization of conjugated dienes, with carbon monoxide, in the presence of free radical generating compounds and, optionally, a compound capable of acting as a hydrogen donor.