Preparation And Properties Of Thermo-reversible Cross-linked Polyethylene

Polyethylene is the world’s largest production of polymer varieties,and crosslinked polyethylene as an important variety of polyethylene resin,cross-linked structure can bring better mechanical properties of polyethylene,high temperature resistance,etc.,which could broad the use of polyethylene.However,the crosslinked polyethylene prepared by peroxide crosslinking,radiation crosslinking and silane water crosslinking are thermosetting materials,which brings challenges to the environment such as difficult recovery and serious pollution.Dynamic chemical bonds for the design and build the crosslinking provides a new train of thought.In this thesis,through designing a functional monomer containing furan group and implementing copolymerization between ethylene and functional monomer,polyethylene containing furan group was synthesized via one-step.Through the Diels-Alder reaction between the polyethylene containing furan group and bismaleimide cross-linking agents,the thermo-reversibly cross-linked polyethylene was obtained the main research contents and conclusions of this paper are as follows:（1）Designed and synthesized an functional monomer containing furan group（6-furan-1-hexene）,respectively in Ziegler-Natta catalyst system and metallocene compound rac-Et（Ind）₂Zr Cl₂ as catalyst,methyl-aluminoxane（MAO）as cocatalyst metallocene catalytic system implementing the copolymerization of ethylene/FH,catalytic systems were studied in detail on the polymerization activity and the content of furan group in polymers,the influence of the thermal properties of polymer and crystallinity.The results showed that the content of furan groups in the polymer can be adjusted flexibly by adjusting the addition amount of FH.In the Ziegler-Natta catalytic system,the content of furan groups in the polymer can be controlled in the range of 0～1.35 mol%,and in the metallocene catalytic system,the content of furan groups in the polymer can be controlled in the range of 0～4.08 mol%.The copolymerization ability and catalyst activity of Ziegler-Natta catalytic system are not as good as metallocene catalytic system,but Ziegler-Natta catalytic system can better maintain the thermal properties and crystallinity of the polyethylene.（2）Reversible crosslinked polyethylene resin was prepared by Diels-Alder reaction between 1,6-bismaleimide hexane（BMH）as crosslinking agent and the copolymer f-PE that was copolymerized in the Ziegler-Natta catalytic system.The effect of the ratio of maleimide group to furan group（M/F）on the mechanical properties of cross-linked polymers was studied in detail.The crosslinking degree of cross-linked polyethylene increases with the increase of M/F（up to 1）.A series of cross-linked polyethylene resins with different crosslinking degrees can be obtained by adjusting the amount of crosslinking agent.Thus,it was preliminarily verified that the furan groups in the copolymer were distributed in the amorphous region of polyethylene,so it was feasible to prepare reversible cross-linked polyethylene resin by Diels-Alder reaction.（3）Based on Diels-Alder reaction between furan groups and maleimide groups,the effects of M/F ratio on the creep properties and re-processability of cross-linked polyethylene resin materials were investigated in detail.The introduction of cross-linked structure of furan group and maleimide can significantly inhibit the creep of the material.The higher the M/F value（the maximum is 1）,the more obvious the creep resistance of the material is.However,for the repeated processing of cross-linked materials,the higher the value of M/F is,the worse the maintenance and stability of the high strength of the cross-linked materials.When the value of M/F is less than 1,it is conducive to the maintenance of the mechanical properties of the materials.