Synthesis and Controlled Organobase-Catalyzed Ring-Opening Polymerization of Morpholine-2,5-Dione Derivatives and Monomer Recovery by Acid-Catalyzed Degradation of the Polymers

Abstract

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.

Hybrid monomer design for unifying conflicting polymerizability, recyclability, and performance properties

“…The current largely unsustainable plastics manufacturing, consumption, and disposal schemes have caused alarming plastics problems associated with their environmental pollution as well as tremendous energy and materials value loss in the economy. [1][2][3][4] Among several approaches being explored [5][6][7][8][9][10][11][12][13][14][15][16] to combat such problems, the development of next-generation, chemically recyclable polymers [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] promises a circular plastics economy approach to address these complex issues. [34][35][36] Monomer design 37,38 is the cornerstone of discovering new circular polymers with intrinsic chemical recyclability, the design of which requires to overcome typical trade-offs between monomer's polymerizability and polymer's depolymerizability, as well as between polymer's recyclability and performance, until a practically useful balance is struck.…”

Prospects of Using Biocatalysis for the Synthesis and Modification of Polymers

“…Polycondensation in aqueous solution is characterized by mild reaction conditions (temperature <80–90 °C, atmospheric pressure) and minimal side processes; however, it is necessary to take measures aimed at overcoming thermodynamic limitations and shifting equilibrium towards polymer formation. In the case of ring-opening polymerization, derivatives of 2,5-diketomorpholine are used as starting monomers; 2,5-diketomorpholine is a cyclodepsipeptide—a condensation product of amino and hydroxy acids [ 188 ]. The most common catalyst used for this reaction is tin(II) octoate (tin(II) 2-ethylhexanoate) This is a typical catalyst for ring-opening polymerization of lactones [ 189 , 190 , 191 ].…”

Well‐Defined Poly(Ester Amide)‐Based Homo‐ and Block Copolymers by One‐Pot Organocatalytic Anionic Ring‐Opening Copolymerization of N‐Sulfonyl Aziridines and Cyclic Anhydrides

“…The thermal stability is almost the same as that of the poly(propylene oxide‐ alt ‐PA) ( T d 5 % of 269 °C), [16] while the T g of poly(TAz‐ alt ‐PA) significantly increase than the poly(propylene oxide‐ alt ‐PA) ( T g of 55 °C), [17] because of amide linkages. Compared with poly[(3S)‐3‐benzyl 6‐methyl‐morpholine‐2, 5‐dione] from ROP of (3S)‐3‐benzyl 6‐methyl‐morpholine‐2, 5‐dione ( T d 5 % of 295 °C, T g of 100 °C), [4a] the decreasing in thermal stability was observed, and the T g of poly(TAz‐ alt ‐PA) increases under the influence of the benzene ring in backbone.…”