The Design Of Block CO₂-based Polycarbonates

Block copolymer can combine the excellent properties of many polymers to obtain better functional materials.It is widely used in biomedical,construction,chemical and other fields.The block CO₂-based polycarbonates are formed by alternating copolymerization of CO₂ and epoxides via subsequent addition of epoxides.The first epoxide monomer copolymerizes with CO₂ to form the first block and after the monomer is completely consumed,the second monomer is added and the second block is synthesized by alternating copolymerization with CO₂.After addition of the second monomer,the system will be doped with trace water.As initiator,water initiates copolymerization of the second epoxide with CO₂ to form selfaggregated polycarbonate,namely by-product,which is difficult to separate and remove from the system.SiO₂ is insoluble in organic solvents,which has hydroxyl structures on surface and is often applied in polymer modification.Based on this,this paper aims to explore the synthetic methods of block CO₂-based polycarbonates.SiO₂ is introduced into the reaction system,and block CO₂-based polycarbonates are grafted onto the surface of SiO₂,while by-products are dissociated in reaction system.After separating by-products via centrifugation and etching by HF,pure block CO₂-based polycarbonates are obtained.This method is used to synthesize different molecular weight,different unit content and different kinds of block CO₂-based polycarbonates.The thermodynamic properties of these polycarbonates are also tested.1.Try to apply hydroxyls of SiO₂ or functional SiO₂ to initiate alternating copolymerization of epoxides and CO₂ to obtain block CO₂-based polycarbonates grafting on SiO₂.The graft reaction is ineffective due to steric hindrance.After optimizing synthetic route,alkynol or enol is applied as initiator for copolymerization of epoxides and CO₂ to obtain block CO₂-based polycarbonates via subsequent addition of epoxides.After removing catalyst,polycarbonates react with silane coupling agent and couple onto Si O₂.The pure block CO₂-based polycarbonates are obtained after centrifugation and etching.The method is tested by 1HNMR,solid-state NMR,element analysis,infrared spectrum and so on,which is proved to be feasible with 40% yield.2.The PCHC-b-PPC block CO₂-based polycarbonates with different molecular weight or unit content are synthesized via the new method.The effects of molecular weight and unit content on the thermodynamic properties of block CO₂-based polycarbonates are investigated by differential scanning calorimetry?DSC?and thermos gravimetric analysis?TGA?.The glass transition temperature?Tg?of low molecular weight polycarbonates increase with the increase of PCHC unit content.The high molecular weight polycarbonates have a very wide glass transition temperature.Four kinds of block CO₂-based polycarbonates are synthesized by changing epoxide monomers.PCHC-b-PiPC and PCHC-b-PHC have a wide glass transition temperature range.The glass transition temperatures of PCHC-b-PSC and PCHC-b-PGC are 105 ? and 70.9 ?,respectively.