The Application Of Click Chemistry To The Modification Of Vegetable Oils

As the rapid development of social economy,problems concerning the pollution of volatile organic compounds and excessive consumption of global petroleum resources appear day by day.Awareness has emerged that these problems not only affect the ecological environment but also hinder the development of organic polymer material industry based on fossil feedstock.To promote sustainable development plans,countries around the world have begun to apply renewable resources to the chemical industry.Among them,vegetable oils are mainly composed of triglycerides,and their fatty acids have 1-3unsaturated double bonds,some of which also contain hydroxyl,epoxy and other reactive groups,so they possess the structural basis for the construction of polymer material system.Vegetable oils can be transformed into a variety of chemical raw materials with high value through chemical modification,such as polyols,polyacids,and epoxy resins and so on.However,many chemical modification methods have various problems such as harsh reaction conditions,long reaction time and low conversion.The solution of these problems is of great significance for the development of plant oil-based materials.The click reactions have numberous characteristics of simple reaction conditions,rapid reaction rate,high yield,harmless by-products,easy separation of products by crystallization and distillation,and no use of solvents or proceeding in benign solvents,and so on.The application of click reaction to the modification of vegetable oils is expected to improve the problems existing in traditional chemical modification methods.This paper mainly studies from the following four aspects:(1)Soybean oil-based polyols were prepared by thiol-ene reaction,and the effect of photoinitiators,reaction time,molar ratio of thiol to carbon-carbon double bond and power of mercury lamp on the structure of the resulting polyols was studied.The effect of different diisocyanates on the thermomechanical,thermal and mechanical properties of polyurethanes from soybean oil-based polyols was investigated.It is found that the optimal reaction conditions are:2 wt%photoinitiator 1173,reaction time of 3 h,ratio of thiol to double bond of 4:1,power of mercury lamp of 300 W.Compared with the polyurethanes from aliphatic diisocyanates,the polyurethanes prepared from aromatic and alicylic ones have better thermal and mechanical properties,including higher glass transition temperature(T_g),thermal stability,tensile strength and Young's modulus.(2)Thiol-ene reaction was extended to other vegetable oils,including olive oil,castor oil,corn oil,canola oil,rice bran oil,grape seed oil and linseed oil.Moreover,four of these polyols were mixed with isophorone diisocyanate(IPDI)to prepare polyurethanes.The effect of hydroxyl value and chemical structure of the polyols on the properties of polyurethanes was investigated,and the structure-function relationship between vegetable oil-based polyols and polyurethanes was established.With the increase of the carbon-carbon double bonds number in vegetable oils,the hydroxyl value of the corresponding polyols increases,and the hydroxyl value ranges from 190 to 305 mg KOH/g.Polyurethanes prepared from vegetable oil based polyols possess properties of wide range from soft rubber to hard plastics.T_g and tensile strength of polyurethanes increase linearly with the increase of hydroxyl value of polyols,while the elongation at break decreases exponentially.(3)The Diels-Alder(DA)reaction of tung oil(TO)and maleimide was used to introduce rigid structure into castor oil-based polyurethane and the effect of DA product content on the thermal and mechanical properties of castor oil-based polyurethanes was investigated.First,for the subsequent preparation of polyurethane,eleostearic acid diethanol amide(EADEA)was obtained by methyl-esterification and amidation.EADEA was then mixed with castor oil,N-(2-hydroxyethyl)-maleimide(HEMI)and IPDI to produce biobased polyurethane-imide in one pot.Through the model reaction of EADEA and HEMI,it is confirmed that DA reaction can proceed between these two during the curing process to generate DA adducts with trialcohol and rigid ring structure.The introduction of DA adducts into castor oil-based polyurethane can significantly increase their thermo-mechanical and mechanical properties,such as T_g,tensile strength and Young's modulus.The tensile strength increases from 1.4 MPa for PU-0DA to 48.2 MPa for PU-60DA.The Young's modulus of PU-60DA is 400 times higher than that of PU-0DA.In addition,the thermal stability of the films is improved.(4)Gallic acid based thiol(GAT)was prepared by chemical modification of gallic acid.The obtained GAT was mixed with diglycidyl ether of bisphenol A(DGEBA)to prepare the biobased thiol-epoxy network(GAT-NEAT)and its shape memory performance was investigated.In addition,to study the effect of different epoxidized vegetable oils on the properties of thiol-epoxy networks,epoxidized linseed oil(ELO),epoxidized soybean oil(ESO)and epoxidized olive oil(EOO)were partly substituted DGEBA to prepare the thiol-epoxy networks.The effect of ELO content on network performance was also explored.GAT-NEAT has good shape memory performance with the shape fixity ratio of98.7%and shape recovery ratio of 97.7%,as well as excellent cycle stability,which can be comparable with petroleum based products.With the addition of epoxidized vegetable oils,the shape fixity ratio is independent of the network structure and remained above 96%,while the shape recovery ratio decreases.