Process for purifying styrene/vinylpyridine copolymer using supercritical carbon dioxide

A process for producing a copolymer of styrene and a vinylpyridine containing 10 to 50% by weight of styrene units having a content of residual monomers less than or equal to 2 ppm from a said styrene/vinylpyridine copolymer contaminated with residual monomers which comprises contacting the said copolymer with supercritical carbon dioxide at a temperature between 35.degree. and 60.degree. C. and at a pressure between 80 and 250 bars for 1 to 6 hours, recovering the entrained extracts at a temperature of between 25.degree. and 30.degree. C. and at a pressure of between 40 and 70 bars, and recovering the purified copolymer.