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We report here a new type of rapidly degradable poly(4-hydroxybutyrate)(P4HB)derivative at room temperature in aqueous solution.The polyester was synthesized via the Passerini multicomponent polymerization(MCP) of (E)-4-oxobut-2-enoic acid with water soluble oligo(ethylene glycol)(OEG)isocyanide followed by hydrogenation.The incorporation of the OEG group at the side chains of P4HB endows the polymer with excellent solubility in water,which makes the polyester degrade in a fully aqueous condition at room temperature.The degradation time decreased significantly from a few weeks to 1 day by changing the degradation condition from a mixture of acetone-d6 and pH 7.4 phosphate buffered D2O(5:1)to pure pH 7.4 phosphate buffered D2O.Based on control experiments with small model compounds,the degradation behavior of the polymer was proven to be almost head-to-tail depolymerization with the formation of a five-membered ring lactone via intramolecular cyclization.A much faster degradation rate in a slightly basic condition(pH 7.4 phosphate buffered D2O)than in a slightly acidic condition(pH 6.8 phosphate buffered D2O)was observed,thus confirming that the intramolecular cyclization was base-catalyzed.