Synthesis And Controllable Study Of Carbon Dioxide Based Aliphatic Polycarbonate

Carbon dioxide(CO2)is the primary ‘greenhouse gas’ and an abundant C1 feedstock.Its co-polymerization with propylene oxide(PO)to produce polycarbonate(PPC)is one of the effective approaches to solve environmental problems and implement green chemistry.However,the poor thermal stability and mechanical properties of PPC obtained via direct polymerisation of CO2 and PO limited its large-scale application.Introducing a third monomer into the CO2/PO co-polymerization system to change the molecular chain structure of the polymer and improve its properties is a popular research subject.Therefore,herein,a heterogeneous composite catalyst,Zn GA/DMC,was successfully prepared and inexpensive,easily available monomers-sorbitol(E420),dodecyl glucoside(APG)and glucose(Glu)-were introduced into the CO2/PO system through the one-pot method for the ternary co-polymerization of PPC-E420,PPC-APG,PPC-Glu.Moreover,CO2-based polycarbonates with good thermal,mechanical and other specific properties were obtained,demonstrating their wide application potential.The main research content and results are as follows:(1)E420 was added into the CO2/PO system as the third monomer to induce ternary co-polymerization to produce polycarbonate PPC-E420 using the composite catalyst Zn GA/DMC,and the effects of reaction temperature,pressure and time as well as the PO/E420 molar ratio on polymerisation were systematically investigated.The yield of PPC-E420 was 71.8gpolym/gcat,and its molecular weight reached 75.4 kg/mol.Introducing E420 changed the chain structure of the polymer,and the result shows that adding E420 evidently improved the thermal properties of PPC-E420.At a 100:5 molar ratio for PO/E420,the maximum thermal decomposition temperature(Td,max)of PPC-E420 could reach 358.9℃,and its glass transition temperature(Tg)could reach up to 53.7℃,notably,this Tg is 22.0℃ higher than that of PPC.Additionally,the mechanical properties of PPC-E420 showed significant improvement: its tensile strength increased from 15.7 to 32.7 MPa,its thermal elongation rate was 51.9% and its permanent deformation rate decreased to 33.2%,showing good dimensional stability and broadening its application fields.(2)Polycarbonate PPC-APG was prepared through the ternary co-polymerization of CO2,PO and APG using composite catalyst Zn GA/DMC,which has high a polymer yield(78.7gpolym/gcat)and a high molecular weight(81.3 kg/mol);in addition,PPC-APG thermal properties are obviously improved.Td,max of PPC-APG is 280.6℃,which is 92.1℃ higher than that of PPC.Tg could reach up to 45.7℃,which is 14.0℃ higher than that of PPC.Furthermore,according to the mechanical properties test,the thermal elongation and permanent deformation rates of PPC-APG reached 97.2% and 62.9%,respectively;these rates are 215.0% and 88.3% lower than those of PPC,demonstrating the good dimensional stability of PPC-APG.Notably,PPC-APG has certain functionality,and its surface tension gradually increases with the increasing solution concentration of APG: the surface tension of PPC-APG5 reached 61.2 m N/m at 0.05 g/m L concentration.This study is therefore highly significant to solving issues such as the greenhouse effect and plastic film printing.(3)Cross-linked network polycarbonate,PPC-Glu,was successfully synthesised via the ternary co-polymerization of CO2,PO and Glu through the one-pot method.Introducing Glu not only improved the thermal and mechanical properties of PPC-Glu but also improved its biodegradability.Compared with PPC,the 5% thermal weight loss temperature(Td,-5%)and Td,max of polycarbonate PPC-Glu increased by 140.4℃ and 190.1℃,respectively,its tensile strength increased from 15.7 to 28.1 MPa and it exhibited lower thermal elongation.The undegraded PPC-Glu had a smooth surface.After being soaked in a phosphate-buffered saline(PBS)solution for seven weeks,PPC-Glu evidently developed many large cavities.Following 10 weeks of degradation,the weight loss rate of PPC-Glu reached 67.1%,which is 62.5% higher than that of PPC.Because the ester group in PPC-Glu broke down to form a carboxyl group during degradation,the acidity of the PBS solution gradually increased,further confirming the reliability of PPC-Glu as a degradable material.