The present invention relates to method for the preparation of a particulate reversibly crosslinked polymeric material comprising: treating a particulate water soluble hydroxyl functional polymer in a liquid phase comprising a solvent mixture in that the hydroxyl functional polymer is insoluble containing an organic solvent and water a tetracarboxylic acid dianhydride represented by formula (I) 10 (I) wherein: U and V are independently selected from CH N and P 15 X is selected from a single bond a saturated divalent (C C) hydrocarbon group O S NR and PR wherein R is selected from hydrogen and (C C) alkyl n and m are independently selected from 0 and 1 w is 1 or 2 with the proviso that 20 if w is 1 then Y is X and if w is 2 then Y is selected from H and (C C) alkyl whereby there is no bond between both Y and optionally a catalyst to form a particulate reversibly crosslinked polymeric material and 25 to a particulate reversibly crosslinked polymeric material obtainable thereby.
