Study On Synthesis And Degradability Of Novel Polycarbonates From α-Alkylidene Cyclic Carbonates

Aliphatic polycarbonates（APC）have received extensive attention in the fields of packaging,biomedicine and tissue engineering due to their good degradability and biocompatibility.For nearly half a century,a series of new functional APC materials have been developed and applied to all aspects of our lifes.Considering the natural resources depletion and global environmental pollution,design and application of APC materials in a green and environmentally friendly manner has become one of the focuses of science research.Carbon dioxide（CO₂）is a renewable,non-toxic and abundant C1 resource.The preparation of APCs by using CO₂ as a carbonylation reagent is an important research field of green chemistry,which is in line with the national strategy of"carbon peaking and carbon neutrality".With the rapid development of CO₂ chemistry,the synthesis of new CO₂-based polymerized monomers and the development of polymerization systems provide a new idea for the indirect utilization of CO₂,which is also an important way to construct CO₂-based APC materials.Based on the previous research of our research group,this thesis intends to develop a new type of efficient organic catalytic system,focusing on a new system for the diverse conversion of CO₂-based-α-alkylidene cyclic carbonate（αCC）.Synthesis of functionalized cyclic carbonates and degradable PC materials through a green and efficient route:（1）A novel organocatalyzed cascade reaction system for indirect utilization of CO₂ was developed.Using CO₂-basedαCCs as starting materials,commercial organic amines as catalysts,and hydroperoxides as nucleophiles,a series of peroxide-substituted cyclic carbonates were efficiently synthesized under mild reaction conditions（TBD:10 mol%,CH₂Cl₂,40 ℃,24 h）.This process features high chemoselectivity and good substrate tolerance.In addition,The mechanism was proved by in-situ infrared experiments etc.The cascade reaction underwent a ring-opening transesterification reaction,a peroxyalcohol hemiketalization reactionand a ring-closing transesterification reaction.The gram-scale reaction and the"one-pot"two-step reaction proved that this catalytic system could indirectly utilize CO₂ and realize the high-value utilization of CO₂.In addition,cyclic carbonates functionalized with peroxide groups could act as free-radical initiators to initiate the free-radical polymerization of styrene.This research work opens up a new reaction pathway for the green synthesis of CO₂-based functionalized cyclic carbonates,and also provides a new idea for the selective chemical degradation of carbonyl-functionalized PC materials.（2）A series of poly（thioether-co-carbonate）materials were designed and synthesized.Using cheap and readily available diols and CO₂-basedαCC as starting materials,a class of vinyl-functional carbonate monomers ware efficiently constructed through a selective transesterification ring-opening process.Furthermore,a series of new degradable PCs（M_n>10kg/mol,（?）=1.1～2.1）were synthesized by using the thiol-ene click polymerization system.By adjusting the chain length of the polycarbonate and the structure of the diol,the glass transition temperature could be adjusted in the range of-20.1～12.3 ℃,and some polymers showed semi-crystalline behavior.Furthermore,based on the reactive properties of the side-chain carbonyl groups,we achieved a chemical selective degradation process of polymers via peroxyalcohols.The polymers are highly reactive and selectively degraded to peroxy-functionalized cyclic carbonates and diol monomers were recovered.This work provided a new way to construct sustainable PC materials.