Study On The Recyclability Of Alicyclic CO₂-based Polycarbonates

Plastics products have become an important part of our life with the increasing demand and application fields of plastics.From the materials that are used to make clothing,houses,cars and aeroplanes to those with sophisticated applications in medicine,diagnostics and electronics,modern life highly relies on plastics.However,the vast majority of these polymers are derived from petrochemicals,which not only lead to the depletion of resources,but also accompany with environment problems.CO₂is an abundant,inexpensive and non-toxic renewable C1 resource,an abundant carbon resource,the alternating copolymerization of CO₂and epoxides is one of the most promising reactions featuring with atom economy.The copolymerization affords CO₂-based polycarbonates with structure diversity and tunability,together with excellent biocompatibility and biodegradability.Therefore,this reaction has received intense interest in academia and industry.This thesis focuses on the development of new methods for the chemical recycle of CO₂-based polycarbonate.Initial investigation on the degradation reaction of CO₂copolymers from pyrroline based epoxides,and it's discovered that the thermal degradation reaction affords epoxide monomers selectively because of the unique ring fused structure in epoxides.Three degradation pathways were designed,solution degradation,thermolysis in presence of catalyst and catalyst free conditions.The substituents in carbamate of CO₂polycarbonates significantly impact on the distribution of degradation products,and it's discovered that the random chain scission occurred initially,and further depolymerization involved the unzipping of the copolymer by an alkoxide backbiting fashion,which can be formed by deprotonation of the hydroxyl chain end resulted from PPNN₃.The introduction of nitrogen atom in the five membered ring fused epoxide significantly impacts their electronic property,bond length and ring strain,which can lead to the unique recyclability for pyrroline epoxides based CO₂polymers.The thesis further has investigated the chemical recycle of various aliphatic CO₂-based polycarbonates catalyzed by a catalytic system consisting of chromium complex based on Schiff base ligand and quaternary ammonium salt PPN-X(PPN=bis(triphenylphosphine)imine,X=azide).We have explored that the effect of reaction temperature,CO₂pressure,types of catalyst and organic base,solvent and catalyst loadings on the conversion and selectivity of degradation reactions,then a possible mechanism was proposed that the recycle of CO₂-based polycarbonates proceeds via a trans-cyclic carbonate intermediate.Finally,a variety of acyclic CO₂based polycarboantes can be recycled back to epeoxides monomers selectively by the design of catalyst and the optimization of degradation conditions.The unique recyclability of CO₂based polycarbonates has expanded their potential application.