Preparation And Properties Of Polymers Of Intrinsic Microporosity Containing Phenylbipyrimidine And Dispirofluorenylanthracene Structures

Nowadays,gas separation membranes have been widely used in the fields of N₂ and O₂ enrichment,H₂ recovery and acid gas removal from natural gas.Traditional membranes exist a trade-off behavior,which means when the gas permeability increases,the selectivity declines,and vice versa.In order to improve the gas permeability and break the trade-off effect of polymer membranes,many novel membrane materials have been reported.Owing to outstanding gas separation performance,polymers of intrinsic microporosity(PIMs)have attracted much attention.Based on the regulation of molecular structure,the relationship between the microphase morphology and the gas separation performance of gas separation membrane is the frontier and hot spot of current research.The establishment of a systematic theory of functional group combination law and the corresponding experimental verification is an important scientific research topic for membrane development in the future.Starting from the design of molecular structure,in this paper,four new kinds of highly rigid tetrahydroxy monomers were designed and synthesized.These monomers were introduced into PIMs and the precise structure optimization and theoretical research of PIM-1 were carried out.First of all,starting from the relationship between structure and performance of polymer,we designed and synthesized a novel"X"shaped slightly twisted rigid nitrogen-containing tetraphenyltetrahydroxybipyrimidine.A series of PIMs(PIM-bpy-x)were prepared through polymerization of tetraphenyltetrahydroxybipyrimidine,tetrafluoroterephthalonitrile(TFTPN)and 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane(TTSBI).The effect of tetraphenylbipyrimidine content on the gas separation performance has been investigated.The results show that the introduction of tetraphenylbipyrimidine improves the anti-aging ability of PIMs.The higher the content of tetraphenylbipyrimidine,the stronger the anti-aging ability of PIM-bpy-x.With the increasing content of tetraphenylbipyrimidine,the Brunauer-Emmett-Teller(BET)surface area of PIM-bpy-x decreases,which is still higher than 650 m² g^-1.The gas permeability of PIM-bpy-x is consistent with the change trend of BET surface area.With the increase of tetraphenylbipyrimidine content,the CO₂ permeability of PIM-bpy-x decreases,but the selectivity for CO₂/CH₄ and CO₂/N₂ increases.PIM-bpy-5 shows the highest CO₂permeability(5141 barrer),which is higher than that of PIM-1.Although the introduction of tetraphenylbipyrimidine improved the gas separation and anti-aging properties of PIMs.However,compared with PIM-1,the gas permeability of PIM-bpy-x is improved slightly.The reason is that the chemical bonds of tetraphenylbipyrimidine unit are single bonds,which can rotate freely.Therefore,the rigidness of the polymer chain was reduced.Introducing the rigid structure of full aromatic ring into polymer chains can improve the gas permeability of polymers.Starting from the molecular structure design,a super-rigid tetrahydroxydispirofluorenylanthracene with two perpendicular plane configurations was designed and synthesized and a series of PIMs(PIM-EN-x)were synthesized based on this monomer.The influence of dispirofluorenylanthracene content on the gas separation performance of PIMs was investigated.The results show that the introduction of dispirofluorenylanthracene makes the chain packing looser,so compared with PIM-1,PIM-EN-_X shows larger chain spacing.PIM-EN-x has a very large BET surface area,ranging from 804 to 895 m² g^-1,which is larger than that of PIM-1.The introduction of dispirofluorenylanthracene increases the micropore content of the polymer,so the gas permeability of PIM-EN-x is much higher than that of PIM-1 without selectivity loss.With the increase of dispirofluorenylanthracene content,the gas permeability increases.The CO₂ permeability and O₂ permeability of PIM-EN-40 is as high as 11512 barrer and 2226 barrer,respectively,which is 2.72 and 2.77 times that of PIM-1.After aged for 193 days,the CO₂ permeability of PIM-EN-30 and PIM-EN-40 is still higher than 6500 barrer,which is much higher than that of unaged PIM-1.Owing to the excellent separation performance of O₂/N₂,CO₂/N₂ and CO₂/CH₄,PIM-EN-x has great application potential in the fields of N₂ and O₂ enrichment,CO₂ capture and natural gas purification.In general,introducing methyl into the building unit is beneficial to further improve the rigidness of the building unit.PIM-EN-x showed very high gas permeability.If dispirofluorenylanthracene can be methylated,the gas permeability of the polymers will be further improved.Starting from the molecular structure design,tetramethyltetrahydroxydispirofluorenylanthracene was designed and synthesized.A series of PIMs(PIM-TMEN-x)were prepared through the polymerization of tetramethyltetrahydroxydispirofluorenylanthracene,TFTPN and TTSBI.The effect of tetramethyldispirofluorenylanthracene content on the gas separation performance of PIMs was explored.Compared with tetrahydroxydispirofluorenylanthracene,the conformation of tetramethyltetrahydroxydispirofluorenylanthracene is more extended,so introducing tetramethyldispirofluorenylanthracene into polymers can reduce the packing density of polymer chain and increase the chain spacing of polymer more effectively.Compared with PIM-EN-x,PIM-TMEN-x has a larger BET surface area,which is in the range of 836-906m² g^-1.The gas permeability of PIM-TMEN-x is higher than that of PIM-EN-x.The CO₂permeability of PIM-TMEN-40 is as high as 12264 barrer,which is higher than the 11512barrer for PIM-EN-40.What's more,PIM-TMEN-40 also shows high gas selectivity.The separation performance of CO₂/N₂,CO₂/CH₄ and O₂/N₂ of PIM-TMEN-x is far beyond the2008 upper bound,which is close to the 2019 upper bound for CO₂/N₂ and CO₂/CH₄ and the 2015 upper bound for O₂/N₂,respectively.Subsequent work further increased the methyl content of dispirofluorenylanthracene.We designed and synthesized octamethyltetrahydroxydispirofluorenylanthracene.The octamethyldispirofluorenylanthracene was introduced into the polymer through nucleophilic polycondensation and a series of PIMs(PIM-OMEN-x)were obtained.The influence of octamethyldispirofluorenylanthracene content on the gas separation performance of PIMs has been investigated.The results show that the introduction of octamethyldispirofluorenylanthracene hinders the polymer chain packing.The chain spacing and BET surface area of PIM-OMEN-x is larger than that of PIM-TMEN-x.BET surface area of PIM-OMEN-x is in the range of 843-913 m² g^-1.PIM-OMEN-x has very high gas permeability and the gas permeability increases with the increase of octamethyldispirofluorenylanthracene content.The CO₂ permeability of PIM-OMEN-40 is as high as 12431 barrer,which is much higher than the 4234 barrer for PIM-1 and also higher than the 12264 barrer for PIM-TMEN-40.After aged for 100 days,the CO₂permeability of PIM-OMEN-x is still higher than 6000 barrer.The CO₂ permeability of PIM-OMEN-40 is as high as 8390 barrer,which is nearly twice that of unaged PIM-1.Base on the previous work,we carried out the precise regulation of polymer chain structure and the effect of the ordered molecular chain segment and the methyl content on the gas separation performance was studied.TFTPN and TTSBI were used to prepare ABA monomer ended with TFTPN.Through the polymerization between ABA monomers with tetrahydroxydispirofluorenylanthraceneandmethyl-substituted tetrahydroxydispirofluorenylanthracene,a series of PIMs(PIM-ABAs:PIM-ABA-EN,PIM-ABA-TMEN and PIM-ABA-OMEN)were synthesized.The results show the introduction of methyl can hinder the chain packing more effectively.With the increasing methyl content,polymer chain is more extended and the BET surface area and pore size of PIM-ABAs increases.PIM-ABA-OMEN has the widest pore size distribution and the largest pore size.The results of molecular dynamics simulation are in agreement with the experimental results.Compared with random copolymers(PIM-EN-x,PIM-TMEN-x and PIM-OMEN-x),PIM-ABAs show higher gas permeability and selectivity.Compared to PIM-OMEN-40,the CO₂ permeability and O₂permeability of PIM-ABA-OMEN increases by 35%at least and the O₂/N₂ selectivity increases by 11%.PIM-ABA-EN has the best permselectivity.Although the CO₂ permeability of PIM-ABA-EN is only 13566 barrer,owing to high gas selectivity,its CO₂/N₂ and O₂/N₂ separation performance is close to the2019 upper bound and 2015 upper bound,respectively.After aged for 186 days,the CO₂permeability of PIM-ABAs is still higher than 8000 barrer,which is almost twice that of unaged PIM-1 and the O₂/N₂ and CO₂/N₂ separation performance of PIM-ABA-EN exceeds the 2015 upper bound and 2019 upper bound,respectively.The excellent gas separation performance makes PIM-ABAs potential gas separation membrane materials.And this work also provides a strategy for the design of molecular structure to prepare brilliant gas separation membrane materials.