ch includes the step of reacting the terminal hydroxyl group of a preformed PLA, PLGA or PGA polymer with a dicarboxylic acid or anhydride, e.g. succinic anhydride or succinic acid (succinylation); the resulting product, which may have a relatively high molecular weight in which case it may be in the form of a gel, facilitates formulation mixing in-situ, and/or may enable easy mixing of a protein