Graft polymers based upon butadiene, alkyl acrylate, methyl methacrylate and styrene, for the improvement of the impact strength of homo- or co-polymers of vinyl chloride. Use is made of a backbone polymer formed of a butadiene-alkyl acrylate copolymer which is agglomerated and grafted with methyl methacrylate, styrene and possibly a cross-linking monomer. The composition, mixtures of homo- or co-polymers of vinyl chloride and graft polymers are usable for the manufacture of plates, bottles, wrapping sheets and bottles for packaging liquids.