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 (C1-C10) hydrocarbon group, O, S, NR, and PR, wherein R is selected from hydrogen and (C1-C4) 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 (C1-C4) 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.
