Synthesis And Crosslinking Of Novel Membrane Materials:Copolyimides

In this study, based on the application of membrane processes on the membrane separation of carbon dioxide, a novel 6FDA-containing copolyimides (i.e. 6FDA- TMPDA/DABA) was synthesized by two-step method for the first time. The yield efficiency could reach up to 95%. They had high molecular weight as well as a specific concentration viscosity value larger than 0.36. They had outstanding properties of heat-resistance with their heat decomposition temperatures higher than 520 慍, moreover, no glass transition temperatures found below 400 揅. They had good solution ability in strong solvents such as NMP, DMF, DMAc etc, and could be used to make membranes. The dense membranes made from 6FDA-TMPDAIDABA 9/1 and 3/1 were investigated. The results showed that the permeabilities and permselectivites of gases in copolymer membranes were between those in homopolymer membranes. The permeabilities decreased but the permselectivities increased with the increase of the content of 3,5-diamino benzoic acid (DABA) in copolymers. ABSTRACT III The 6FDA-TMPDAIDABA 9/1 copolyimide was crosslinked by chemical crosslinking using diethylene glycol and good results were obtained for both processes---posttreatment crosslinking and conventional crosslinking. The CO2 permeability of posttreatment crosslinking membrane changed little. The permselectivies of C02/N2 and CO2ICH4 were up to 22.3 and 28.3 respectively. However, crosslinked copolyimide membrane by conventional crosslinking, the permeabilities of all the measured gases increased to different extent. Among them, the permeabilities of C02, N2 and CH4 increased greatly, and reached to 151 Barrer, 8.21 Barrer and 6.99 Barrer respectively. The permselectivities of C02/N2 and C02/C1-14 reached to 18.4 and 21.6 respectively. The 6FDA-TMPDAIDABA 9/1 copolyimide will possibly become the membrane material of suppressing plasticization and excellent properties.