“One-Pot” Synthesis Of Block Copolymers Based On Ring-Opening Copolymerization Of Epoxides

With the steady progress of national policies such as Plastic Limit Order and the Green Development,it’s meaningful to exploit biodegradable polymer materials.Compared with non-degradable materials,synthetic biodegradable-based polymers suffer from low performances and high cost,which limit their applications.Ring-opening copolymerization（ROCOP）of epoxides and CO₂/anhydrides allows the synthesis of biodegradable polycarbonates/polyesters with well-defined structures,precise molecular masses and low distributions under mild conditions.Combining with the other living polymerization techniques for the synthesis of block copolymers has provided the unique opportunities for fine-tuning the properties of polycarbonates/polyesters and realizing the preparation of high-performance,low-cost biodegradable-based materials.By now,the synthetic methods for block copolymers mainly require multi-step process,like additional separation and purification,which is time-consuming and low efficiency.Moreover,the structure types of the above block copolymers are limited to polycarbonate-b-polycarbonate,polycarbonate-b-polyester and polyester-b-polyester.Therefore,it remains challenges to design catalysis systems with high activity and selectivity,establish novel one-pot strategies for the synthesis of block copolymers and enrich the structure diversity of the block copolymers.In this dissertation,four new methodologies for one-pot synthesis of polycarbonate/polyester-based block copolymers from the monomer mixture have been proposed,namely“bifunctional chain transfer”,“auto-tandem catalysis”and“switchable polymerization”,which combine reversible addition-fragmentation chain transfer（RAFT）polymerization,organometallic mediated radical polymerization（OMRP）based on the desinged porphyrin aluminum complexes and bi-Schiff based cobalt complexes as the catalysts.Main results and conclusions are summarized as below:（1）CO₂-based polycarbonate-b-polymethacrylate block copolymers were synthesized by bifunctional chain transfer reaction.Using porphyrin aluminum complex(TPP^2-Cl)Al^III-Cl as the catalyst for ROCOP of epoxides/CO₂ and the trithiocarbonate compound bearing acarboxylic group（TTC-COOH）as the bifunctional chain transfer agent,CO₂-based polycarbonate-b-polymethacrylate block copolymers were obtained from the mixture of epoxides,CO₂ and methacrylates.The double chain transfer effect allowed for independent and precise controlled over the molecular weight of each block with narrow polydispersities.The axial group exchange reaction between(TPP^2-Cl)Al^III-Cl and TTC-COOH impeded the formation of homopolycarbonates.Bifunctional chain transfer strategy for one-pot synthesis of CO₂-based polycarbonate block copolymers was established.（2）Polyester-b-polymethacrylate block copolymers were synthesized by auto-tandem catalysis reaction.Aluminum porphyrin complexes(TPP^2-Cl)Al^III-X（X=Cl,OAc and OMe）were designed for the development of photoinduced electron/energy transfer reversible addition-fragmentation chain transfer（PET-RAFT）polymerization.Combining the initiation effect of aluminum porphyrin complexes on ROCOP of epoxides/anhydrides,(TPP^2-Cl)Al^III-Cl was chosen as the bifunctional catalyst for PET-RAFT and ROCOP.Well-controlled PET-RAFT polymerization of methacrylates and ROCOP of epoxides/anhydrides occurred in a sequential or concurrent manner with the regulation of visible light,obtaining polyester-b-polymethacrylate block copolymers from the monomer mixture.Auto-tandem catalysis strategy for one-pot synthesis of polyster-based block copolymers was established.（3）CO₂-based polycarbonate-b-polyacrylate-b-poly（vinyl acetate）block copolymers were synthesized by O₂-triggered switchable polymerization.A bi-Schiff based cobalt complex（Salen）Co^II was exploited as the smart catalyst and oxygen as a molecular trigger,which allowed the switchable polymerization from OMRP of non-conjugated vinyl monomers to ROCOP of epoxides/CO₂.The unprecedented mono-oxygen insertion reaction in radical manner was rationalized by density functional theory（DFT）calculations and comparative experiments,leading（Salen）Co^III-R transfers to（Salen）Co^III-OR rapidly and quantatively.Starting from（Salen）Co^III-poly（vinyl acetate）as macroinitiator,CO₂-based polycarbonate-b-polyacrylate-b-poly（vinyl acetate）block copolymers were selectively synthesized from the monomer mixture.O₂-triggered switchable polymerization strategy for one-pot synthesis of CO₂-based polycarbonate block copolymers was established.（4）Polyester-b-polyacrylate block copolymers were synthesized by CO-triggered switchable polymerization.Using a bi-Schiff based cobalt chloride complex（Salen）Co^III-Cl as the catalyst and CO as a molecular trigger,a facile strategy that switched from ROCOP of epoxides/anhydrides to OMRP of vinyl monomers was described.The proposed mechanism,which involved CO coordination and migratory insertion,was rationalized by model reactions and DFT calculations.The rapid and quantitative insertion of CO into the Co-O bond allowed for in situ transformation of the ROCOP active species（Salen）Co^III-OR into the OMRP photoinitiator（Salen）Co^III-CO₂R.With the regulation of CO and light,well-defined polyester-b-polyacrylate block copolymers were obtained from the mixture of epoxides,anhydrides and acrylates.CO-triggered switchable polymerization strategy one-pot synthesis of polyester-based block copolymers was established.