Preparation Of Thermoreversible Cross-linking Polypropylenes

Polypropylene(PP)is one of the most important resins with wide applications and highyield.Cross-linked structure can provide PP with more excellent mechanical properties,solvent resistance and low temperature resistance,and broaden its application fields.However,the current cross-linked pp is mostly thermosetting pp,and the cross-linked state is irreversible,which causes processing and reusing problems.This paper demonstrate the preparation of the thermoreversibly isotactic polypropylene,by designing and synthesizing a series of functional olefin comonomors containing furan groups(furyl-?-olefin)and implementing the propylene/furyl-?-olefin copolymerization,and then bulding the cross-linked structure via Diels-Alder click reaction between the furan groups in PP chains and the bismaleimide.The main research content and the correspongding results are as follows:(1)Designed and synthesized a series of furyl olefin monomers with different carbon chain lengths: 4-furyl-1-butene(FB),5-furyl-1-pentene(FP),6-furyl-1-hexene(FH)and8-furyl-1-octene(FO).The Ziegler-Natta catalytic system was used to initiate the copolymerization of propylene(P)with furyl olefins.The effect of furyl olefin monomers on the copolymerization reaction was studied in detail.The results show that the copolymerization activity shows the rule of FB <FP <FH <FO,and the copolymerization kinetic curves are similar to the propylene homopolymerization,which rising first and then decreasing and decaying slowly.In the copolymerization system of P/FO and P/FH,the polymerization activity is higher than that in the propylene homopolymerization.(2)The effect of the furyl olefin monomer structure on the reactivity ratio was studied,and it was compared with the copolymerization of propylene and corresponding ?-olefins(1-octene,1-hexene,1-pentene)without furan substituent.The comparison of reactivity ratio shows that the reactivity ratios of comonomers in the copolymerization reactions involving FO are higher than that of 1-octene.After analysis,it is believed that the result is caused by the increase of monomer diffusion rate;the reactivity ratio of propylene in P/FO copolymerization is also significantly increased.This paper believes that the increase in the content of polypropylene long sequence is the reason for giving the copolymer a higher melting point and melting enthalpy.By changing the concentration of furyl olefin monomers in the reactant,the content of the furyl pendent groups in the copolymer can be adjusted between 1.96 and 5.01 mol%,thereby laying a foundation for the design of polypropylene crosslinking degree.(3)Based on the Diels-Alder reaction between maleimide and furan,micromoleculebismaleimide was used as a cross-linked agent to react with the synthetic polypropylene containing furyl pendent groups to prepare a series of thermoreversibly cross-linked plypropylene resin.The effects of structure of micromolecule bismaleimide,maleimide /furan ratio and furyl content in polypropylene on the mechanical properties of cross-linked polypropylene were studied.The results show that the introduction of cross-linking in polypropylene can significantly improve the mechanical properties of the material,and the polymer properties can be further adjusted by changing the degree of cross-linking,Thus the feasibility of solving the contradiction between the mechanical strength and the processing efficiency of polypropylene by using this research scheme has been preliminarily verified.