Study On Network Polyimide Gas Separation Membrane Based On Truxene-triamine

Networked polyimide（PI）membrane materials have important potential applications in the field of gas separation membranes due to their excellent thermal stability and good resistance to plasticization.In our previous work,we prepared a series of network PI materials via an in-situ one-step crosslinking method and applied it to the area of gas separation membranes.However,this method often leads to excessive contraction of the pores between PI chain segments with the huge sacrifice in gas permeability,and also possesses the high risk of gelation tendency.In view of this,a new triamine monomer（hexahexyl-truxene-triamine,HTUTA）with hexyl side chain was designed and synthesized in this paper,the introduction of hexyl side chains into the network PI materials can effectively reduce the cross-link density of the network PI materials and improve the gas permeability of the membrane materials,as well as reduce the intermolecular forces between the polymer chain segments and inhibit the tendency of gelation during their preparation.Then,three kinds of network polyimide films（truxene-based network PIs,TUBN-PIs）were prepared by condensation reactions with ODPA,BTDA and 6FDA monomers,respectively.1)All three prepared TUBN-PIs films have good thermal stability properties(decomposition temperature T_d,10%>425°C and glass transition temperature in the range of 198-269°C).Among them,HTUTA-6FDA containing-CF₃ structure has the best gas separation performance with a gas permeability of 93.94 Barrer for CO₂.This is mainly due to the enhanced gas permeability caused by the further inhibition of the effective stacking of molecular chains by-CF₃.Compared with the TAPB-6FDA membrane material without side chain structure,the gas permeability of HTUTA-6FDA to CO₂ and O₂ was improved by 261%and 253%,respectively.2)Then,we further improved the gas permeation properties of the TUBN-PIs membrane materials by copolymerizing 2,4,6-trimethyl-1,3-phenylenediamine（DAM）or 2,3,5,6-tetramethyl-1,4-phenylenediamine（TMPA）monomers.This is mainly due to the fact that the introduction of the copolymer monomer increases the free volume of the polyimide material.The results showed that the best gas permeability was achieved in the case of HTUTA:DAM=3:2.In detail,the CO₂ permeability was151.52 Barrer,which improved about 61.29%than that of HTUTA-6FDA,and still maintained the decent ideal selectivity for CO₂/N₂=19.94.