Polydepsipeptides (PDPs) are strictly alternating copolymers of α-hydroxy acids and α-amino acids produced via the ring-opening polymerization (ROP) of morpholino-2,5-dione derivatives (MDs). They have been used as promising biomaterials for their combined high thermal stability and good mechanical properties of polyamides as well as the inherent degradability of polyesters. ROP of MDs is usually carried out at high temperatures with metal catalysts or enzymes, with less control over the polymer molecular weights and dispersities. In this work, we developed a simple and efficient synthetic strategy of a new platform MD via the Passerini-type reaction between an isocyano derivative of the amino acid and an aldehyde, followed by intramolecular esterification. Nine new MDs were synthesized by using this method, and the organobase-catalyzed ROP of these MDs was investigated. When the ROPs of these MDs were catalyzed by either triazabicyclo[4.4.0]dec-5-ene (TBD) or diazabicyclo[5.4.0]undec-7-ene (DBU) in the presence of benzyl alcohol as an initiator, the polymerizations were uncontrolled with the formation of both linear PDPs and cyclic PDPs. By using binary catalytic systems of 1-(3,5-bis(trifluoromethyl)-phenyl-3-cyclohexyl-2-thiourea) (TU) with DBU or TBD ([TU]/[TBD] or [DBU] > 3), the polymerizations became well-controlled, allowing the synthesis of PDPs with controlled molecular weights, low dispersities, as well as block copolymers. Furthermore, cyclic PDPs were obtained when the ROP of these MDs was catalyzed with TBD in the absence of both TU and an initiator. Finally, we used two methods to recover the monomer precursors or pure MD monomers: the TBD-catalyzed alcoholysis of PDPs was very fast and generated the monomer precursors quantitatively, while the acid-catalyzed depolymerization of PDPs led to pure and quantitative monomer recovery.

Self‐immolative polymers are a special kind of degradable polymers that depolymerize into small molecules through a cascade of reactions upon stimuli‐triggered cleavage of the polymer chain ends. This work reports the design and synthesis of a fluoride‐triggered self‐immolative polyester. A 2,4‐disubstitued 4‐hydroxy butyrate is first confirmed to quickly cyclize in solution to form a γ−butyrolactone derivative. Then, the Passerini three component reaction (P‐3CR) of an AB dimer (A: aldehyde, B: carboxylic acid) with tert‐butyl isocyanide or oligo(ethylene glycol) isocyanide affords two poly(2,4‐disubstitued 4‐hydroxybutyrate) derivatives (P2 and P3). Two silyl ether end‐capped polymers (P4 and P5) are abtained from P2 and P3, and their degradation in solution is examined by NMR spectrum and size exclusion chromatography. Polymers P4 and P5 are stable in the absence of tetrabutylammonium fluoride (TBAF), while in the presence of TBAF, the molar masses of P4 and P5 gradually decrease with time together with the increase of the amount of formed 2,4‐disubstitued γ‐butyrolactone. The depolymerization mechanism is proposed. The first step is the fast removal of the silyl ether by fluoride. Then, the released hydroxyl group initiates the quick head‐to‐tail depolymerization of the polyester via intramolecular cyclization.

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