[ONXO](x=S,N)CrY-Mediated The Synthesis Of Polycarbonate,Polyester And Polycarbonate-Block-Polyester Copolymer

The ring-opening copolymerization?ROCOP?of epoxide with CO₂ or anhydride provides a low energy,green and environmentally friend route for the preparation of biodegradable polycarbonate and polyester.In this context,to design new type of functional aliphatic polyester and polycarbonate as well as develop high active and selective catalyst systems is a key topic.Based on this,the main contents of this paper were summarized as follows:Four kinds of metal Salalen analogues of[ONSO]CrY?Y=Cl,N₃?complexs were synthesized.These complexes assisted by ammonium salt were employed for the copolymerization of cyclohexene oxide?CHO?and CO₂.The results demonstrated that the complexes with electron-withdrawing subsitutents are beneficial for enhancing catalytic activity and polycarbonate selectivity.Moreover,the effect of reaction conditions such as temperature,amount of cocatalyst on copolymerization activity,the carbonate linkage and molecular weight were systematically investigated.A proposed copolymerization mechanism was assumed according to the kinetic study and end group analysis.Novel aliphatic polycarbonates with a tunable number of cyclic carbonate?CC?and epoxide?EP?dual functional groups were synthesized via an[ONSO]CrCl-mediated selective copolymerization of 4-vinyl-1-cyclohexene diepoxide with CO₂ in one pot.The content of pendant CC and EP groups could be conveniently adjusted by varying the molar ratio of PPNCl to[ONSO]CrCl and the reaction temperature,in which the EP is varied in the range of 30⁷0%.The resultant EP and/or CC-functionalized polycarbonates can undergo multiple postpolymerization modifications with amine,NaN₃ or HCl either individually or sequentially in a one-pot process,providing an extensive library of functionalized polycarbonate derivatives with hydroxyl-or azidoalchol-,and hydroxyurethane-functional groups.A facile strategy has been demonstrated for the selective synthesis of highly stereoregular polyesters with cis-2,3-?exo,exo?,trans-2,3-?exo,endo?or cis-2,3-?endo,endo?repeating units by the organocatalysts?PPNCl,N-MeIm et al?mediated alternating copolymerization of CHO and norbornene anhydride?NA?stereoisomers.The geometrical structure of polyester can be tuned simply by modulating the type of NA isomers?endo-or exo-NA?,monomer feed ratio,and reaction temperature.The resulting polyesters provide a versatile platform to incorporate various functional groups?-COOH,-OH,-NH₂?through the robust thiol-ene reaction of the pendant norbornenyl groups.A?ONSO?CrCl complex-based binary catalyst for efficient ring-opening copolymerization?ROCOP?of epoxide and norbornene anhydride?NA?in a stereoselective manner to afford polymers with variable stereoisomerism is reported.The role of?ONSO?CrCl complex on the cis/trans selectivity of resulting polyester as well as enhancement of the reaction rates has been revealed.The formation of chelates between the endo-diester unit of the polyester chain and the metal center plays a determinate role in the stereoselectivity of the 91%cis-?endo,endo?-polyester in solution copolymerization of endo-NA with CHO in the presence of metal complex.Additionally,the stereostructure of resulting polyester is also dependent on the polymerization method,NA type,electronic effect of epoxide and the bulkiness of the substituent of the formed ester units in the polyester chain.Accordingly,a proposed mechanistic pathway for the stereostructure formation of polyesters is provided.Stereoblock copolymers composed of atactic carbon dioxide-based polycarbonate and stereoregular variable polyester were successfully synthesized via sequential ring-opening copolymerization?ROCOP?of CHO with norbornene anhydride?NA?isomers and then ROCOP of CHO with CO₂ under?Salcy?CrCl/PPNCl binary catalyst.Notably,the CO₂suppresses the configuration transformation from cis-?exo,exo?to trans-?exo,endo?of polyester has been revealed in the sequential ROCOP.Using this strategy,stereospecific polyester with the almost fully cis-2,3-?exo,exo?-poly?NA-alter-CHO?was achieved in the ROCOP of exo-NA with excess CHO in the presence of CO₂ catalyzed by PPNCl.A probability of the role of CO₂ in restraining the geometric transformation from cis-?exo,exo?to trans-?exo,endo?was proposed.A preferential depolymerization of polyester-block-polycarbonate has been revealed under DMAP/CHO catalyst system,where the degradation process undergoes in three steps with the poly?cyclohexne carbonate??PCHC?block degrading into trans-cyclcohexne carbonate?trans-CHC?in the first stage,followed by the occurrence of simultaneous degradation of PCHC associated with polyester segment in the second stage and then polyester degradation at the last.Noteworthy,a stereotransformation from cis to trans for polyester block is occurred during the degradation process.Interestingly,such transformation could be tuned by CO₂.Other variations influencing the polyester-block-polycarbonate degradable behaviors were systematically investigated.