Study On The Preparation Of Epoxidized Natural Rubber Grafted With Ploy (Ethylene Glycol) Monomethylether Carboxylic Acid And The Properties Of Composites Polymer Electrlyte

Polyethylene oxide?PEO?is a traditional matrix material of polymer electrolyte.The PEO polymer has flexible chains and low T_g,which can conductive the mirgation of Li⁺in the polymer.Except that,there are lots of-CH₂CH₂O-in the PEO chains,which can coordination with Li⁺and improve the compatibility of alkali metal salts with matrix.It is widely used in the research of polymer matrix.Its greatest advantage lies in forming a stable lithium salt complex without any plasticizing agent.But the easy crystallization characteristics of PEO leads to decrease of ionic conductivity.Now the modification of polymer matrix was studied more and more widely.A flexible backbone can be grafted with the PEG containing ether bond and its derivaties,the good electrical properties and the mechanical properties of polymer electrolyte materials can be prepared.Firstly,mPEGCOO-g-ENR was prepared by the grafting reaction of ENR and mPEG-COOH.The mPEG-COOH side groups grafted to ENR50 by esterification and comb like copolymer was prepared.Infrared spectra and proton nuclear magnetic spectra showed that the grafting reaction successfully.Compared with mPEG-COOH,the melting temperature,the melting enthalpy and the normalized crystallinity of mPEGCOO-g-ENR are greatly reduced,at the same time,the glass transition temperature?T_g?decreased with increase of mPEG-COOH content.The series of composite polymer electrolyte were prepared by using mPEGCOO-g-ENR as the CPE matrix,LiClO₄ as lithium salt.The ionic conductivity of CPE increases with the increase of mPEG-COOH content.When mPEG-COOH content is 80phr,the magnitude of the ionic conductivity of mPEGCOO-g-ENR/LiClO₄CPE can reached to 10^-5 S/cm.The properties of mPEGCOO-g-ENR/LiClO₄ can be analysised by the equilibrium swelling method and XRD.The results showed that lithium salt not only provide the free Li⁺,but also can be used as a crosslinking agent which complexation with ENR 50 and mPEG-COOH.The ionic conductivity of CPE affected by the mPEG-COOH content.The ionic conductivity of CPE increases with raising mPEG-COOH content.The ionic conductivity reaches the maximum of 8.93×10^-5 S·cm^-1.And the mechanism of Li⁺transportation in the CPE is explained by the equivalent circuit.The most suitable molar ratio of mPEGCOO-g-ENR/LiClO₄-IL in the system was explored by adding differernt molar ratio of LiClO₄-IL.After the electrochemical test,when the molar ratio of LiClO₄-IL is 1:0.5,the Li⁺and IL have the strongest effect.There exists more free Li⁺,so the ionic conducity of CPE can improved.FTIR spectra and ¹HNMR spectra proved that IL will indeed interact with LiClO₄ and compete with the complexation between-CH₂CH₂O-and Li⁺,which can weaken the complexation and release more free Li⁺,so the ionic conductivity of CPE increased.Field emission scanning electron microscopy and XRD analysis showed that with the increasing of ionic liquid?IL?,lithium perchlorate crystals are gradually decreased,which proved that adding IL is conductive to the dissoaciation and disperseration of LiClO₄,so the ionic conductivity of mPEGCOO-g-ENR/LiClO₄-IL CPE increased.On the basis of above,the grafting reaction of ENR 50 and different molecular weight mPEG-COOH was studied.The performance of different molecular weight of grafted mPEGCOO-g-ENR was investigated by ATR-FTIR and DSC analysis.The CPE was prepared by using mPEGCOO-g-ENR as matrix and adding LiClO₄-IL.The characterization,electrical properties and mechanical properties of CPE were analyzed by universal tensile machine,FESEM,DSC,TGA and AC impedance.The results showed that the initial decomposition temperature of mPEGCOO-g-ENR 550,mPEGCOO-g-ENR 2000 and mPEGCOO-g-ENR 5000 polymer electrolyte all higher than 200°C,which can meet the requirements of application of lithium ion battery.By studying on the mechanical properties of materials,its mechanical properties will be improved because of cross-linking.And when the molecular weight of mPEG-COOH is 5000,the tensile behavior of MPEGCOO-g-ENR 5000/LiClO₄-ILCPE is similar to glassy polymers.With the increase of molecular weight,the crystallization trend of mPEG-COOH increased significantly.The long flexible chain formed a certain crystallization in the system,which can cause the yielded phenomenon of in the tensile behavior of polymer electrolyte.The electrical test results showed that the electrical properties of polymer electrolyte changed with different molecular weight,the ionic conductivity of mPEGCOO-g-ENR 2000/LiClO₄-ILCPE can reach to 9.52*10^-5S/cm.If side chain is too long,there will be lots of coordination crosslinking point.It can restrict the increase of ionic conductivity.