Expandable elastomeric material in the presence of water or oil

A process for the preparation of an elastomer capable of swelling in oil and/or in water and brine comprising the steps of:

• a) making an aqueous inverse emulsion of particles of a polymer comprising a betaine group prepared by inverse emulsion polymerization of monomers Ab comprising a betaine group, optionally other monomers Ba and a small quantity of polyvalent, preferably divalent or trivalent monomers Ca, comprised in an aqueous phase dispersed in the form of droplets in a hydrophobic external phase having hydrophobic surfactants, the molar ratio of the monomers Ab to the optional monomers Ba being between 4/96 and 40/60, preferably 7/93 and 30/70, the molar ratio of the polyvalent, preferably divalent or trivalent monomers Ca per mole of polymer which would have been obtained without the addition of monomers Ca, being between 1.5 and 10, preferably between 2 and 4, and
• b) compounding said elastomer with the aqueous inverse emulsion obtained by step a).