Preparation And Polymerization Property Analysis Of Lignin-Based Polymerizable Monomers With Different Molecular Weights

Development of bio-polymer to replace petroleum-based polymer has become one of the research hotspots at home and abroad.Lignin is an important renewable resources with rich aromatic ring structure,and can be used to synthesize bio-based macromolecule monomers.Therefore,developing polymerizable lignin-based monomers and its polymers has important research significance and is an important way to high-value utilization of lignin.In this study,Indulin AT lignin was used as raw material and fractionated by organic solvent and by organic solvent-gel chromatography.Lignin components with different relative molecular weights were obtained.Then,the lignin-based polymerizable monomers with different molecular weights were prepared by reaction of graded lignin with vinylethylene carbonate to introduce polymerizable double bond functional groups into lignin.The effect of relative molecular weight distribution of lignin on the introduction of double bonds was investigated.Finally,the lignin-based polymerizable monomers were polymerized by reversible addition-fracture transfer(RAFT),and the effect of the molecular weight distribution of the lignin-based polymerizable monomers on the polymerization performance was clarified.The main conclusions are as follows:Four kinds of lignin components(acetone dissolved lignin,sediment(I),sediment(?),sediment(?)were successfully isolated by the organic solvent method.The yield of the products was 42%,5.8%,14.3%and 17.2%,respectively.According to the order of relative molecular weight,sequence is as follows:sediment(?)>Indulin AT>sediment(?)>acetone dissolved lignin>sediment(?).Compared with the Indulin AT lignin,the graded lignin have higher carbon content and lower oxygen content.In sediment(?),the carbon content is 68.15%,and oxygen content is 21.94%.After grading,the content of aliphatic hydroxyl group decreased from 2.02 mmol/g to 1.52 mmol/g,and the content of phenolic hydroxyl group increased from 2.88 mmol/g to 3.85 mmol/g.The thermal stability of lignin is related to the relative molecular mass distribution.The higher the relative molecular mass of lignin,the higher the carbon residue rate.In addition,compared with the organic solvent method,the medium pressure rapid preparation system has the advantages of simple operation,more uniform and repeatable lignin separation,and the chemical structure of the separated components is the same as that of the original lignin,which provides a feasible technical scheme for the industrial application of lignin classification.However,due to the excessive lignin components separated,the subsequent experiments are not conducive to the use of experimental operations,so the components separated by organic solvent method are used as reactants in the subsequent experiments.The suitable conditions for the reaction of lignin fractions with vinylethylene carbonate are:reaction temperature 150?and reaction time 1 h.Infrared spectra show that the double bond unit has been successfully introduced into lignin molecule.Compared with the Indulin AT lignin,the graded lignin molecular has higher grafting efficiency.Compared with the graded lignin(sediment(?),sediment(?)and sediment(?)),the smaller the relative molecular weight of lignin components,the higher grafting efficiency of double bond due to the smaller steric hindrance,the more alcohol hydroxyl groups introduced.Besides Indulin AT lignin,the thermal stability of the graded lignin was improved after the introduction of the double bond.The smaller the relative molecular mass of the lignin,the greater the influence on the thermal stability.The effect of different monomer/chain transfer agent/initiator ratios on the polymerization of sediment(?)/VEC was investigated.The suitable ratio is 50:1:1.For Indulin AT/VEC and sediment(?)VEC with larger molecular weight,the polymerization effect is not obvious,due to higher steric hindrance.However,for acetone dissolved lignin/VEC,sediment(?)/lignin VEC and sediment(III)/VEC,polymerization of three lignin-based monomers is react.Among them,the polymerizable monomer sediment(?)/VEC has the most remarkable effect and the molecular weight of the polymer increases obviously.Thermodynamic analysis showed that the thermal stability of the copolymers was higher than that of the monomers after the copolymerization of the sediment(?)/VEC monomers with lower molecular weight.The results show that the relative molecular weight of Indulin AT lignin is about 1000,and the content of total hydroxyl and phenolic hydroxyl is higher.After grafting,more hydroxyl is introduced,the grafting rate is higher and the aggregability is better.