Studies On The Preparation And Chemical Recovery Of Polyester From Diols And Aromatic Dialdehydes

Global production of plastics accounts for a significant portion of polymer materials,with the use of disposable plastics in particular proliferating as society progresses.However,although disposable plastics bring convenience,hygiene and safety to people,they have also caused widespread concern about environmental pollution,such as "white pollution" and "microplastic pollution".Therefore,it is a hot topic of research in the social,scientific and economic fields to develop sustainable and recyclable polymer materials.In recent years,the rapid development of chemically recyclable polyester is a viable strategy for solving the above problems,which not only achieves a true closed-loop chemical cycle,but also an atomically economical and less polluting method.In all respects,this chemically recyclable strategy is beneficial to the future development of the plastics industry and will certainly provide important ideas for the future of human production and life.This work focused on the synthesis of high molecular weight and precisely modifiable polymers by means of homopolymerization and copolymerization using inexpensive diols and dialdehydes as monomers,using a new green and environmentally friendly synthesis method.A systematic study was conducted on the thermal properties of copolymers copolymerized with diols,as well as the influence of the microstructure of polyester on the thermal properties.The hydrogenative cycle recovery of copolymer was investigated.A speculated mechanism for dehydrogenative polymerization and hydrogenative depolymerizative was proposed.Also,We have innovatively completed the polymerization of aromatic dialdehyde,explored the polymerization conditions and synthesized high molecular aromatic polyester,and studied the chemical recycling of aromatic polyester.(1)Copolymerization between long-chain aliphatic diol 1,10-decanediol and various short-chain aliphatic diols and cyclic diols was used,and it is found that diol dehydrogenative copolymerization can synthesize polymers with molecular weight up to 65.9 kg/mol in an efficient and green way.The copolymerization effect of various monomers and the effect of different monomers on the thermal properties of the polymer were also investigated.The differences between the "H-H","H-T" and "T-T" linkages were analyzed in detail by NMR spectroscopy,and the results showed that the differences in structure and linkages had a significant effect on the thermal properties of the polymers.Finally,the chemical recycling of polyesters under various conditions was investigated and it is found that dehydrogenative copolymerization and hydrogenative depolymerization under solvent-free conditions could be perfectly integrated within the same catalytic system.The monomer recovery rate of the secondary cycle is as high as 95%,and the polymer obtained from the repolymerization of the recovered monomer has almost no loss of properties,also only hydrogen removal and addition occur throughout the chemical cycle without any by-products.(2)Aromatic polyesters were synthesized using aromatic dialdehyde as the material for polymerization,and the Tishchenko coupling polymerization reaction conditions using acridine-based ruthenium catalyst were explored.The polyester molecular weight of 38.3 kg/mol can be synthesized when the amount of catalyst is 2mol%.Compared to conventional polymerization methods,this reaction process is green and highly atomic economical with no addition of substances other than solvents,monomers and catalysts,moreover the reaction conditions are relatively mild.Based on the good small molecule experimental results of furfural,we further realized the efficient coupling polymerization of heterocyclic aromatic dialdehydes(2,5-diformylfuran),and the better rigidity and thermal properties of aromatic polyesters make them promising for certain applications.Finally,for aromatic polyesters a reversible hydrogenative depolymerization back to the monomer is also accomplished,and the new small molecular compounds are recovered through chemical cycling.