Study On The Synthesis And Modification Of Isosorbide Based Bio-polycarbonate

The conventional process of synthesizing polycarbonate(PC)from the petroleum-based compound bisphenol A(BPA)and phosgene has several disadvantages due to the estrogenic effect of BPA and the high toxic volatility of phosgene.Currently,the novel pathway to synthesize bio-polycarbonate through one-step direct melt polycondensation of biomass-derived isosorbide(ISB)and CO2-derived dimethyl carbonate(DMC)has become a hot research topic for high-performance polycarbonate.Because this process is not only green and non-toxic,but also can produce polycarbonate with more excellent optical properties,scratch resistance and heat resistance than traditional bisphenol A polycarbonate.However,the synthesis of high molecular weight poly(isosorbide carbonate)(PIC)via this method remains a considerable challenge due to the weak reactivity of ISB,the methylation reaction of DMC,and the rigid structure of ISB,which leads to the poor mechanical flexibility and processability of PIC and limits its engineering application.In view of the above difficulties,we conducted the following work,and the main research contents and innovative achievements are as follows:(1)A series of organic alkali metal catalysts were screened,and the effects of different organic alkali metals on the catalytic activity of ISB and the selectivity for carboxymethylation of DMC were investigated.The binding energy of cation-anion of the catalyst and its ability to activate the substrate were studied by using density functional theory(DFT)simulation,nuclear magnetic resonance spectroscopy(NMR),fourier infrared spectroscopy,mass spectrometry(MS),and other analysis methods,and the theoretical basis for the design of the catalyst was obtained.In addition,the end group structure of PIC oligomer and final polymerization products were characterized by NMR.Finally,based on the intermediates captured and detected in PIC synthesis,a possible synergistic mechanism of cation-anion and hydrogen bond was proposed.(2)Combined with the designability of anion and cation of ionic liquid(IL),a series of dual active site IL catalysts with phenolic group as anions,[N1111]+,[N2222]+,[N3333]+,[N4444]+as cations were designed and synthesized,and high molecular weight PIC was synthesized through screening their activities.The effects of the type,number and steric hindrance of active sites on the catalytic activity were studied by DFT simulation.Finally,the alternative addition reaction path of DMC and ISB was confirmed in combination with the intermediates captured during transesterification stage,which provided theoretical support for the study of reaction mechanism of PIC synthesis from DMC and ISB.(3)A series of IL catalysts with[Py]-,[Im]-and[Tr]-as anions and[N2222]+,[Emim]+ and[P4444]+ as cations were designed and synthesized to further improve their catalytic activity for PIC synthesis,and their chemical structures and thermal stability were characterized.It was found that[Emim][Im]showed the highest reactivity among the ILs,and high molecular weight PIC with the molecular weight of 55100 g/mol was obtained with a 98%conversion of ISB under the optimized reaction conditions.In addition,the in-situ NMR spectroscopy was employed to full-scale and in-depth investigate the reaction process of synthesizing PIC at different temperatures.The effect of reaction conditions on the methylation reaction of DMC was investigated.Finally,a possible mechanism for the synergistic catalysis of cation-anion was proposed in combination with the interaction between substrates and IL catalysts observed with NMR.(4)Finally,a new one-step copolymerization method was proposed,which could shorten the polymerization process and improve efficiency.A series of aliphatic and aromatic diol monomers were screened for synthesizing PIC copolymers,and a PIC copolymers with molecular weight of 80300 g/mol was synthesized after the optimization of aromatic diol monomer ratio.The relationship between the Tg of PIC copolymers and the ratio of different carbonyl carbons was found by NMR and thermal analysis results,which indicated that the thermal properties of PIC could be directionally adjusted.In addition,The DMA results showed that the introduction of aromatic diol monomers effectively improved the flexibility of PIC and reduced the rigidity of PIC.The copolymerization process not only greatly improved the flexibility and processing performance of PIC,but also maintained high thermal performance.