Composition having improved thermomechanical properties, and a method of cross-linking it

The present invention relates to a composition that is extrudable and cross-linkable in air. The composition that is extrudable and cross-linkable in air comprises a mixture of a copolymer with an ethylenically-unsaturated compound and an unsaturated ester, a hydrolizable silane compound having no ethylenic unsaturation containing functional groups, and a thermoplastic polymer having no functional groups, said functional groups of the ester being selectively reactive with the functional groups of the silane compound. Such a composition is used to fabricate a material for insulating or sheathing a power cable, in particular a medium-voltage cable or a cable for working at a voltage of less than 20 kV. The invention also provides method enabling said composition to be cross-linked and power cables including insulation and/or a sheath containing the composition obtained by the method.