Design And Synthesis Of Ethylene-propylene Rubber With Reversible Cross-linking Function

Ethylene/propylene copolymer(EP rubber,EPR)is an important kind of synthetic rubber and cross-linked structure brings EPR excellent physical and chemical properties.Sulfur vulcanization is currently the main cross-linking method for EPR,but its irreversibility causes recycling and reusing problem.This article demonstrates an efficient method to synthesize thermoreversible cross-linked EPR,by firstly designing a functional olefin comonomer containing furan group(FO)and implementing the ethylene/propylene/FO terpolymerization catalyzed by a widely used Ziegler-Natta catalyst,and secondly building the cross-linked network via Diels-Alder(DA)click reaction between the bismaleimide and pendant furan groups in EPR chains.The conclusions are described as follows:(1)This method can directly control polymer structures such as copolymer composition,furan group content,molecular weight of polymer by adjusting polymerization conditions,which will help to construct well-defined and tunable EPR module to study their reversible cross-linking.~1H-NMR showed that the third monomer insertion rate gradually increased with the increase of initial third monomer addition.(2)The cross-linking density can be adjusted by furan content in terpolymer as well as the bismaleimide/furan ratio.FTIR result indicated that the formed DA crosslinks broke at elevated temperature(>110?C)and was re-formed at relatively low temperature(<85?C).DMA result showed that compared to the linear EP rubber without any cross link,the cross-linked EP rubber can tolerate higher temperature and the modulus of the rubber networks can be recovered upon cooling procedure to fulfill the DA coupling reaction.The tensile tests showed that compared to EP rubber without any cross link,the cross-linked EP rubber showed higher Young's moduli and lower elongation values at break.(3)A facile local-repairing of crack was applied in thermoreversible cross-linked EP rubber and its tensile properties were compared to EP rubber without any destruction.The result showed that EP rubber can be repaired by the local repairing of crack and the mechanical propertied can recover to a certain extent,which provided a new idea for the application of reversible cross link.