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.

Abstract: This invention relates to copolymers of a macromolecular compound having a non-halogenated and double-bonded chain and of a vinylaromatic monomer and the process for obtaining same. The reaction between the macromolecular compound and the vinylaromatic monomer takes place at a temperature of between -80.degree. C and +40.degree. C in the presence of 5.10.sup.-4 to 5.10.sup.-2 mol/l of a Lewis acid initiator and possibly in the presence of a co-initiator. These copolymers obtained by cationic grafting are thermoplastics elastomers.