| With the rapid development of science and technology,people benefit from the advantages and enjoy electronic,intelligent and convenient lives,meanwhile,people cause increasingly serious environmental problems.The release of petroleum,natural gas and automobile exhaust generates a large amount of carbon dioxide gas,which has caused the greenhouse effect.In order to resolve the conflict between energy use and environmental protection,people have made great efforts and fabricated many environmentally friendly materials for the capture and conversion of small molecular gases such as carbon dioxide.Porous polyimides have become an important part of porous organic polymers(POPs)due to their outstanding thermal and chemical stabilities,large specific surface areas as well as rigid permanent porosities and nitrogen-oxygen rich structures.The construction of three-dimensional network in porous materials frameworks is a prerequisite for the formation of porous channels.Thus the establishment of porous polyimide channels often requires rigid building blocks to provide extended structures,and fine reaction conditions to optimize the porosity parameters,however,porous polyimide are limited by geometry configuration of building blocks and tedious experimental operation.Hyperbranched polyimides(HBPIs)tend to form effective dense stacking and cause the collapse of polymer skeletons due to chain entanglement from the isotropic globular structures,which is disadvantageous for the formation of pore channels.Crosslinking reaction is an important approach to obtain porous materials,and the skeleton structures and pore channels of HBPIs can be supported and formed through alkynyl crosslinking reactions at high temperatures.The pore structure for small molecules gas capture is easily fabricated by alkynyl crosslinking reaction and can come from abundant monomers with alkynyl groups.Porphyrin-based building blocks provide planar,rigid,large ?-conjugated structures and easy-to-chelate metal properties,which support the framework of porous materials.Taking advantage of the cross-linking characteristics of alkynyl functional groups at high-temperature,and using porphyrin-based tetramines with excellent thermal and skeletal stability as building blocks,we introduce alkynyl functional groups as crosslinking nodes in porphyrin-based hyperbranched polyimide skeleton to obtain crosslinked porphyrinbased polyimides and optimize the porosity parameters.From the perspective of molecular design,we explore the effect of the following factors on the porous structure of crosslinked porphyrin-based polyimides,including metal-chelation sites,spatial configuration(conjugated and molecular sizes)of terminal anhydrides and dianhydrides,as well as alkynyl crosslinking sites in the side/main chains and the alkynyl groups crosslink density,in order to optimize their porosity parameters and enhance CO2 uptakes.It is divided into the following four parts for explanation.Firstly,crosslinked porphyrin-based polyimides(PPBPI-CRs)are prepared from 5,10,15,20-tetra(4-aminophenyl)porphyrin(TAPP)and 2,5-bis(3,4-dicarboxyphenoxy)-4'-phenylethynyl biphenyl dianhydride(PEPHQDA)using alkynyl groups as crosslinking nodes via a two-step reaction.The chemical structural characterization is confirmed by FT-IR and 13 C CP/MAS NMR.DSC and TGA analyses are investigated to explore the occurrence of crosslinking reaction and showed excellently thermal properties in polyimides skeletons.The SEM and TEM are used to study the surface morphologies and pore channels.Compared to PPBPI-Mn-CR and PPBPI-Fe-CR,PPBPI-H-CR reveal higher specific surface area(733 m2 g-1)and CO2 uptake(2.26 mmol g-1).PPBPI-Mn-CR and PPBPI-Fe-CR have declined BET surface area and more uniform pore sizes as well as higher CO2 isosteric enthalpies of adsorption due to the presence of coordination sites for manganese and iron.PPBPI-VIICRs exhibit separation factors of CO2/N2(31.48,35.09 and 45.34)and CO2/CH4(13.17,9.06 and 12.99).In the chapter,the porosity parameters,CO2 uptakes and selectivities of PPBPI-CRs can be regulated by changing metal-chelating sites.Secondly,the spherical structures of HBPIs facilitate the introduction of functional terminal groups to modify and improve the property of HBPIs.The spatial configuration(molecular and conjugate sizes)of building blocks hold an important part in the optimization of porosity parameters.Crosslinked porphyrin-based polyimides are fabricated to explore the effect of molecular and conjugate sizes in different terminal alkynyl anhydrides on the porosities based on alkynyl group crosslinking reactions.Affected by ?-stacking and molecular sizes effect,with increasing conjugate and molecular sizes effect in different terminal anhydrides,porphyrin-based polyimides(PPBPIs)reveal decreased specific surface areas(106.8 – 8.3 m2 g-1),whereas,PPBPICRs showed increased BET surface areas(1.8-633 m2 g-1).Meanwhile,PPBPI-CRs have considerable CO2 uptakes(1.37,2.01 and 2.37 mmol g-1)and isosteric heats of CO2 adsorption(34.8,27.5 and 22.6 k J/mol).The PPBPI-CRs have CO2/N2(39.83,36.95,40.08)and CO2/CH4(14.13,9.78,10.87)separation selectivities.The spatial configuration of terminal anhydrides is an important factor for the porosities in PPBPICRs networks.Moreover,the spatial position of alkynyl groups in the side/main chains has an impact on the alkynyl crosslinking sites in porphyrin-based polyimides(PPBPIs).5,10,15,20-tetra[4-[(3-aminophenyl)ethynyl]phenyl]porphyrin(TAPEPP)with alkynyl functional groups is synthesized and used as crosslinking nodes.A series of crosslinked porphyrin-based polyimides(PPBPI-CRs)are synthesized from TAPEPP and several dianhydrides via polymerization and crosslinking reactions.PPBPI-CRs exhibit excellently thermal and chemical stabilities.Meanwhile,PPBPI-CRs reveal decreased Brunauer-Emmett-Teller(BET)surface areas(628-115 m2 g-1)and enlarged pore sizes with increased conjugate and molecular sizes of dianhydrides.Moreover,PPBPI-CRs have carbon dioxide uptakes(0.67-2.33 mmol g-1 at 273 K and 1 bar)and CO2 isosteric enthalpies of adsorption(19.7-29.6 k J mol-1)as well as CO2/N2 selectivities(42.5,32.21,36.91 and 74.65).Above all,PMDA in PPBPI-PM benefits the formation of microporous structure due to moderate conjugate and molecular size.Finally,we focus on the effect of alkynyl crosslinking density on the porosities in PPBPI-CRs.A novel dianhydride 3,3'-bis(3,4-dicarboxyphenoxy)-4,4'-diphenylethynyl biphenyl dianhydride(BPEBPDA)with high alkynyl content is successfully synthesized.BPEBPDA has two alkynyl groups on biphenyl-structure sides.Porphyrin-based polyimides(PPBPIs)with different alkynyl crosslinking densities are synthesized from BPEBPDA and porphyrin-based building blocks(TAPP and TAPEPP)via polymerization reactions.PPBPI-CRs are obtained from PPBPIs through thermal crosslinking reactions.The PPBPI-CRs exhibit BET surface areas(682 m2 g-1 and 693 m2 g-1)and CO2 uptakes(2.0 mmol g-1 and 1.67 mmol g-1 at 273 K and 1 bar)as well as the separation factors of CO2/N2(37.63,28.97)and CO2/CH4(7.51,5.61).Meanwhile,PPBPI-CRs show an enhanced CO2 isosteric enthalpies of adsorption(25.1 k J mol-1 and 30.1 k J mol-1)than other porous polymers.The higher CO2 adsorption value,CO2/N2(37.63,28.97)and CO2/CH4(7.51,5.61)of PPBPI-1-CR is probably due to the larger micropore volume(0.155 cm-1 g-1)and the higher micropore volume ratio(micropore volume/total pore volume = 0.361)than those of PPBPI-2-CR(0.147 cm-1 g-1,0.322).The high alkynyl crosslink density increases the probability of the formation of pore channel in the space region,but the steric hindrance of the polyimide backbone causes the chain blockage to make high alkynyl crosslink density ineffective.The reasonable distribution of alkynyl groups in the polyimide backbone is the key factor for porosity parameters of crosslinked polymers,we will figure it out in our future work.In this thesis,in order to enhance CO2 adsorption and separation performance,using porphyrin-based tetramines as the building block,and crosslinkable alkynyl functional groups as crosslinking unit,we fabricate PPBPI-CRs and optimize their porosity parameters by changing metals-chelating sites and alkynyl crosslinking-sites,introducing terminal anhydrides,as well as adjusting spatial configuration of dianhydrides and enhancing alkynyl crosslinking density.This thesis theoretically provides several optimization factors for porosities in crosslinked porphyrin-based polyimides,but it also faces some problems.These problems need to be solved in the future experimental process.The study of PPBPI-CRs can provide theoretical guide for the design,synthesis and application of environmentally friendly materials,and have potential application in the field of CO2 adsorption,storage and separation. |
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