| Isosorbide(1,4:3,6-dianhydro-D-glucitol;Is)is a bio-based monomer that has achieved industrial production.It has been used in the fields of drugs,cosmetic solvents,and polymerization of polymer polyesters and polycarbonates.Isosorbide as a monomer to participate in the polymerization reaction can first reduce the use of fossil-based monomers,reduce the pressure of environmental protection and energy depletion;secondly,there are two V-type furan rings in the isosorbide molecule,and the molecular structure has great rigidity.The polyester synthesized from isosorbide has a high glass transition temperature.However,isosorbide has a large steric hindrance and low reactivity during high-temperature melt polycondensation.It is difficult to prepare polymers with high molecular weight and low yellowing,which is a key bottleneck limiting its large-scale application.Therefore,researchers usually use isosorbide as a comonomer component to modify the existing polymer materials in a low proportion to ensure that the products have high molecular weight and acceptable color.In order to study the effect of impurities contained in bio-based isosorbide on its esterification and polymerization reaction,this topic uses isosorbide and adipic acid(AA)to prepare polyisosorbide adipate(PIA)by stepwise polycondensation as a model reaction to study the effect of reaction conditions on polymerization and optimize the polymerization process.Using the established optimized reaction conditions,the effect of trace impurities on polymerization was further studied by’reverse addition’method.The main research contents and conclusions are as follows:(1)Construction and process optimization of PIA polyester model reaction from isosorbide and adipic acidPIA polyester was prepared by esterification-melt polycondensation.The type and amount of catalyst,esterification temperature,purge rate,stirring rate and alcohol-acid ratio in the esterification process were changed by control variable method.The esterification process was studied and evaluated by titration to determine the conversion rate,chromaticity and ultraviolet spectrum.The polycondensation temperature,polycondensation time,catalyst and alcohol-acid ratio of the polycondensation process were changed by controlling the variable method to explore the effect of polycondensation conditions on the properties of the polymer.The molecular weight of PIA polyester was characterized by GPC.The results showed that the polymerization process of isosorbide was affected by many factors.By optimizing the polymerization process of PIA polyester,the polymerization process of PIA polyester was finally determined:alcohol-acid ratio 1.2:1,catalyst tetrabutyl titanate 1000 ppm,esterification temperature 200°C,purge rate 70-80 m L/min,stirring rate 200 rpm,reaction 210 min,polycondensation temperature 260°C,polycondensation 120 min.The PIA polyester obtained under this condition has the best performance,and its performance is also improved compared with the reported PIA polyester.(2)Effect of impurities on isosorbide PIA polyesterUnder the optimized process,the impurities contained in isosorbide:isomannide(1,4:3,6-dianhydro-D-mannitol,Im)and D-sorbitol were added to the reaction system in reverse,and the effects of impurities on the polymerization of PIA polyester were determined by titration,ultraviolet spectroscopy,GPC,DSC and ~1H NMR.The results show that the addition of impurities has little effect on the conversion rate of PIA polyester esterification process,which is mainly due to the excessive alcohol system in the homopolymerization process,and the impurities mainly affect the polycondensation stage of PIA polyester.In the polycondensation stage,the impurities affect the molecular chain of the PIA polyester by inserting the molecular chain segment and blocking the molecular chain.The thermal properties of PIA polyester were affected by destroying the order and regularity of molecular chain structure.According to the results of ~1H NMR,as the amount of impurities increases,the effect on the structure is more serious,which in turn affects the other properties of PIA polyester.The above work shows that process optimization is helpful to improve the performance of isosorbide polyester,and it is helpful to obtain more widely used isosorbide polyester in process production.It also proves that the impurities carried in isosorbide will also have a serious impact on the performance of the polymer.If isosorbide is fully purified in industrial production,it will also help to improve the performance of the polymer. |
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