Synthesis Of Thermoreversibly Cross-linked Ethylene/propylene Rubbers And The Cross-linking Reaction Kinetics

As an important variety of synthetic rubber,ethylene-propylene rubber?EPR?is widely used in people's daily life and industrial production.As we all know,the cross-linked structure can give rubber products excellent performance,but the most common vulcanization or peroxide cross-linking process has brought environmental problems such as difficult handling of rubber waste and serious pollution.In recent years,the use of dynamic covalent chemical reactions to construct reversible cross-linked polymers to solve the problem of difficult recycling of traditional cross-linked materials has attracted increasing attention.In this thesis,by designing a functionalized olefin monomer containing a furan substituent and performing ternary copolymerization with ethylene and propylene,an ethylene-propylene rubber containing furan groups was synthesized.And then,through the Diels-Alder reaction between the polymer and bismaleimide cross-linking agents,the thermoreversibly cross-linked EPR was obtained,and the kinetics of the cross-linking reaction was studied in detail.The research contents and conclusions of this paper are as follows:?1?Designed and synthesized functionalized olefin monomer 8-furan-1-octene?FO?,and by using metallocene compound rac-Et?Ind?₂ZrCl₂ as the catalyst and methylaluminoxane?MAO?as the promoter to initiate the ternary copolymerization of ethylene/propylene/FO.The effect of promoter/catalyst ratio?Al/Zr ratio?on the copolymerization was studied in detail.The results show that when n?MAO?:n?FO?>1,the copolymerization activity is higher than ethylene/propylene binary copolymerization,and the FO conversion rate and polymer molecular weight both increase first and then decrease with the increase of Al/Zr ratio;when Al/Zr=4000,the ternary copolymerization has the characteristics of high activity and high FO conversion;furthermore,by adjusting the concentration of FO in the reaction system,a series of EPDM rubber with adjustable furan content from 2.25 to 9.79 mol%can be obtained;?2?Reversible cross-linking was carried out by using bismaleimide cross-linking agents with three different structures(BM_Ph2,BM_C6 and BM_C12),and performing the Diels-Alder reaction with the EPDM obtained previously containing furan groups;the effect of maleimide/furan ratio?M/F?on the degree of rubber cross-linking and the mechanical properties of the resulting material were studied in detail.The results show that the degree of cross-linking and mechanical strength of the material increase with the increase of M/F?up to1/1?,and cross-linking networks with different tightness can be obtained by controlling M/F;the thermal reversibility of the Diels-Alder rings formed between the maleimide and furan groups give the cross-linked rubber the ability to be repeatedly processed and molded,and its mechanical properties can be maintained stably,thus a series of EPR with thermoreversible cross-linking function can be obtained.?3?The kinetics of the reversible cross-linking reaction was studied in detail through the rheological test,and the reaction rate constant k_CL and Arrhenius activation energy E_a,CL of the cross-linking reaction were calculated.The results show that to a certain extent?70⁹0°C?,increasing the cross-linking temperature is conducive to promoting the completion of the cross-linking reaction;due to the rigid molecular structure of the BM_Ph2,its E_a,CL values participating in the cross-linking reaction are significantly higher than the system including BM_C66 and BM_C12;the value of M/F also has a significant effect on the E_a,CL,CL of the cross-linking reaction.It is believed that the change in furan content directly affects the functionality of the polymer molecule as a reactant.Based on this conclusion,the E_a,CL,CL of the cross-linking reaction can be reduced by increasing the furan equivalent,which will be instructive for the efficient implementation of reversible cross-linking.