A process for the preparation of an aqueous slurry comprising a plurality of copolymer particles suspended therein, the process comprising at least the steps of: a) providing a reaction medium comprising an organic diluent, and at least two monomers whereby at least one monomer is an isoolefin and at least one monomer is a multiolefin; b) polymerizing the monomers within the reaction medium in the presence of an initiator system to form a medium comprising the copolymer, the organic diluent and optionally residual monomers; c) contacting the medium obtained in step b) with an aqueous medium comprising at least one LCST compound having a cloud point of 0 to 100°C and removing at least partially the organic diluent and to the extent present in the medium removing at least partially the residual monomers to obtain the aqueous slurry comprising the copolymer particles; wherein the amount of LCST compound(s) present in the aqueous medium employed in step c) is of from 1 to 1,000 ppm with respect to the amount of copolymer present in the medium obtained according to step b); and wherein the aqueous medium contains 20.000 ppm or less of non-LCST compounds whereby the non-LCST compounds are selected from the group consisting of • ionic or non-ionic surfactants, emulsifiers, and antiagglomerants; • salts of (mono- or multivalent) metal ions; • carboxylic acid salts of multivalent metal ions; • stearates or palmitates of mono- or multivalent metal ions; or • calcium and zinc stearates or palmitates; with respect to the amount of copolymer present in the medium obtained according to step b). a) providing a reaction medium comprising an organic diluent, and at least two monomers whereby at least one monomer is an isoolefin and at least one monomer is a multiolefin; b) polymerizing the monomers within the reaction medium in the presence of an initiator system to form a medium comprising the copolymer, the organic diluent and optionally residual monomers; c) contacting the medium obtained in step b) with an aqueous medium comprising at least one LCST compound having a cloud point of 0 to 100°C and removing at least partially the organic diluent and to the extent present in the medium removing at least partially the residual monomers to obtain the aqueous slurry comprising the copolymer particles; wherein the amount of LCST compound(s) present in the aqueous medium employed in step c) is of from 1 to 1,000 ppm with respect to the amount of copolymer present in the medium obtained according to step b); and wherein the aqueous medium contains 20.000 ppm or less of non-LCST compounds whereby the non-LCST compounds are selected from the group consisting of • ionic or non-ionic surfactants, emulsifiers, and antiagglomerants; • salts of (mono- or multivalent) metal ions; • carboxylic acid salts of multivalent metal ions; • stearates or palmitates of mono- or multivalent metal ions; or • calcium and zinc stearates or palmitates; • ionic or non-ionic surfactants, emulsifiers, and antiagglomerants; • salts of (mono- or multivalent) metal ions; • carboxylic acid salts of multivalent metal ions; • stearates or palmitates of mono- or multivalent metal ions; or • calcium and zinc stearates or palmitates;