Design And Processing Methods Of Microporous Organic Polymer Membranes

Microporous organic polymers are widely used and demonstrated excellent performance in the fields of hydrogen storage,selective adsorption and separation,electrochemical energy conversion,transistors,etc.due to their high BET surface area,continuous nanochannels,and adjustable physicochemical properties.However,most microporous organic polymers are either difficultly transformed into membranes by solution or melting processing,or the stability of the microporous structure after processing is poor.These problems limit the application of microporous organic polymers in membrane technology.Therefore,aiming to expand the processing approaches of microporous organic polymers,this paper prepares a series of novel functionalized microporous polymers through technology optimization and molecular design,which are applied in the fields of membrane technologies including separation membrane and ion exchange membrane.The details are as follows:1.PIM-1 is a typical polymer of intrinsic microporosity(PIMs)and possess excellent solution processability,however,its microporous structure is susceptible to organic solvents and gases,resulting in pore swelling and subsequent weakened molecular sieve ability of membranes.In this work,acylchloride-functionalized PIMs(PIM-COCl)was synthesized and coated on the aminated polyacrylonitrile ultrafiltration membrane to fabricate sandwich-like organic solvent nanofiltration membrane via interfacial crosslinking.When the concentration of PIM-COC1 was 0.10wt%,the increase of interfacial crosslinking degree hardly affected the alcohol flux of membranes,but the crystal violet rejection had a significant improvement.The alcohol flux of membranes was 5.2 L m-2 h-1 bar-1,meanwhile,crystal violet rejection was 94%.The stability test demonstrated that the interfacial crosslinking could prepare stable microporous layer at the interface,which simultaneously improved the molecular sieve ability and organic solvent-resistance of microporous structure.2.Solvation-driven self-crosslinking of PIM-1 at low temperature was explored by the virtue of low organic solvent-resistance.Firstly,the solvation for PIM-1 backbone of superacid enhanced the movement ability of rigid polymer chains and further increase the distance between polymer chains.Subsequently,superacid promoted the cyclotrimerization of cyano group to achieve low-temperature and fast self-crosslinking process of PIM-1 for the first time without long-term high-temperature treatment.With the assistance of swelling and crosslinking,the packing of PIM-1 chains were rearranged into a "wide-cavity/thin-gate" structure.The XRD,SAXS and PAL results indicated that increasing concentration of superacid,elevating treatment temperature and prolonging treatment time would result in growing pore width of cavities and gradually shrunk gate size.As a result,in the comparison of original PIM-1 membrane,the optimal 3-SCPIM-6/24 membrane only exhibited a slight decline of CO2 permeability from 4375 barrer to 4008 barrer,but a significant improvement of CO21N2 and CO2/CH4 permeability selectivity from 21.4 to 25.1 and from 16.0 to 40.9,respectively.Combining the good result of aging test,these results superacid-catalyzed self-crosslinking is beneficial post-modification strategy for cyano-containing PIMs materials.3.Through research on the Friedel-Crafts hydroxyalkyl polymerization of electron-rich multi-benzene and benzaldehyde derivatives,a family of functionalized poly(phenyl-alkane)s of intrinsic microporosity were designed and prepared.The spirobisindane structure was found to possess self-inhibition feature in the Friedel-Crafts hydroxyalkyl polymerization,therefore,spirobisindane-based multi-benzene could react with benzaldehyde derivates to form linear microporous polymers.The electron-withdrawing substituents on benzaldehyde could improve the polymerization degree for high-molecular-weight polymers,meanwhile,the distribution of substituents influenced the degrees of rotational freedom of polymer chains to tune the BET surface area.For instance,low-degree of rotational freedom PIM-3c possessed far higher BET surface area(1 189 m2 g-1)than those(685 m2 g-1 and 472 m2 g-1)of high-degree of rotational freedom PIM-3a and PIM-3b.4.Based on the research of poly(phenyl-alkane)s of intrinsic microporosity,aldehyde-substituted N-heterocycles were used instead of benzaldehyde derivatives to prepare alkaline PIMs.The viscosity and film-forming test revealed that the polymerization degree increased with the increase of pKa of N-heterocycles.Additionally,compared with conventional high temperature proton exchange membranes(HT-PEMs),phosphoric acid(PA)-doped polybenzimidazole membranes,imidazole-containing PIMs combined imidazole moiety and microporous structure to achieve high PA doping level and low volume swelling,which are features of ideal HT-PEMs.At the same PA doping density,imidazole-containing PIM membrane with high micropore content possessed far higher proton conductivity,indicating that microporous structure offered continuous PA-doped nanochannels to promote proton transfer by the PA-based hydrogen bond network.5.Covalent organic frameworks are a class of crystalline porous materials with well-defined nanochannels.In this work,we prepared a clear DMSO/H2O sol of amorphous ionic polyimine nanoparticles and fabricated crystalline ionic COF nanosheet membrane through the sol-gel process.During the solvent evaporation,the amorphous ionic polyimine nanoparticles were transformed into the crystalline ionic COF nanosheets via reversible aldimine condensation and confinement effect.The crystallinity of ionic COF nanosheet membranes could be tuned by the proportions of DMSO/H2O mixed solvents,and resultant ionic COF membranes exhibited different water contact and proton conductivity.The proton conductivity of crystalline ionic COF membrane was far higher than that of amorphous ionic COF membrane,supporting that well-organized and interconnected nanochannels could effectively reduce the proton transport resistance.This work further enhanced the combination of microporous polymers and membrane technology through the synthesis and post-modification methodology of functional microporous polymers,in order to stabilize the microporous structure of microporous polymers;In addition,we pioneered the preparation of stable sols with crystalline covalent organic frameworks,thereby enhancing its solution processing ability.The combination of microporous polymer and membrane technology provided a theoretical and technical basis for the design and preparation of next-generation membrane technology.