Abstract: Elastomers with thermoplastic properties consist of polymers grafted on an elastomeric chain which includes double bonds and active sites. The latter are more particularly halogen atoms, especially chlorine, and the grafted polymer is a polyindene or a copolymer of indene with styrene derivatives, such as .alpha.-methylstyrene or para-alkyl-styrene. In the process for preparing these thermoplastic elastomers the choice of constituent proportions, catalyst and solvent is important. Elastomers possessing at 80.degree. C. a breaking strength of at least 60 kg/cm.sup.2 can be obtained.