A Low-temperature Crosslinking Strategy To Maintain The Morphology And Microstructure Of Low-dimensional Polymers Containing Benzene Ring And Its Application

Linear polymers containing benzene ring are made into various low-dimensional materials with well-defined nanomorphology and microstructure due to their good solubility and melt fluidity.However,the high solubility of linear polymers containing benzene ring in most polar organic reagents and complete decomposition at high temperatures when carbon replicas cannot be obtained limit their application in efficient separation and removal of light oils,organic solvents,organic dyes and other pollutants whose high toxicity and low degradation seriously affect the ecological environment,as well as the application of carbon replicas in the fields of adsorption and energy storage.Therefore,achieving a high degree of crosslinking on the basis of maintaining the original nanomorphology and microstructure of low-dimensional polymer containing benzene ring is the key to achieving the above mentioned applications.In this paper,from the perspective of reducing the solubility of linear polymers containing benzene ring and rapid crosslinking,the original nanomorphology and microstructure of low-dimensional aromatic polymer materials are maintained,and low-temperature rapid crosslinking strategy is developed.This crosslinking strategy was used for low-temperature crosslinking modification of low-dimensional linear polystyrene（PS,a typical linear polymer containing benzene ring）material,and successfully maintained the original nanomorphology and microstructure.Based on this,the application research of hollow crosslinked PS fiber membrane in organic solvent-water separation,cationic dye purification and the exploration of the preparation of carbon replicas of low-dimensional PS materials were investigated.details as follows:（1）First,Friedel-Crafts low-temperature rapid crosslinking system that maintains the original nanomorphology and microstructure of low-dimensional aromatic polymer（PS）materials is developed.The crosslinking reaction system consists of solvent（n-hexane）,catalyst（anhydrous Fe Cl₃）and crosslinking agent（diethoxymethane）.The characteristics of the crosslinking system are:n-hexane has very weak solubility for PS;diethoxymethane has high reactivity;anhydrous Fe Cl₃ is insoluble in n-hexane,and the weak complexation with anhydrous Fe Cl₃ ensures that Fe Cl₃ shows high catalytic activity in crosslinking reactions at low temperature.The results demonstrated that at room temperature the linear PS replayed a high crosslinking reaction rate in the crosslinking system;the obtained crosslinked zero-dimensional PS microspheres maintain the isolation and perfect spherical structure of the original linear PS microspheres;cross-linked one-dimensional hollow PS fibers（HPFs）maintain a straight,loose and hollow tubular fiber structure;a two-dimensional membrane composed of cross-linked HPF（HPF-C）maintains the original size,porosity and macroporous structure.And the mechanical strength has been significantly improved,while showing excellent solvent resistance,lipophilicity and hydrophobicity.（2）The representative strongly soluble organic solvents toluene（lighter than water）and chloroform（heavier than water）are mixed with water,and then the HPF-C membrane is used to separate the organic solvent-water mixture,showing an excellent organic solvent-water separation capacity and high organic solvent flux.In addition,with cross-linked HPFs and PS microspheres as precursors,the corresponding carbon replicas of the original morphology and microstructure are obtained through super crosslinking and high temperature pyrolysis,having high specific surface area,unique porosity and a certain degree of graphitization which enable the material to have potential application prospects in the fields of adsorption and energy storage,and further research is needed.It can be seen that this low-temperature crosslinking strategy provides a new way for the research and application of low-dimensional linear polymer containing benzene ring with different nanomorphologies.（3）The HPF-C membrane contains a large number of benzene ring structures,and each benzene ring has multiple C-H reaction sites,which can be negatively modified through chemical reactions for filtering and removing cationic organic dyes.First,room temperature crosslinking reaction is used to control the microporous structure of HPF-C,and then high density sulfonic acid groups are introduced through sulfonation to achieve negative modification,which is then used for the adsorption and removal of cationic dyes in aqueous solutions.The results show that the obtained sulfonated HPF-C（HPF-C-S）membrane has excellent hydrophilicity and good selectivity to cationic dyes（methylene blue-MB,basic red-BR46 and safranine T-ST）adsorption:for the BR46 aqueous solution with an initial concentration of 50 mg L^-1,the HPF-C-S membrane showed an equilibrium adsorption capacity of up to 443.6 mg g^-1.The adsorption of MB template dye on the HPF-C-S membrane is achieved through electrostatic interaction andπ-πstacking,following pseudo-second-order kinetics and monolayer adsorption（Langmuir adsorption isotherm model）,which is a spontaneous physical adsorption process.The maximum adsorption capacity(346.0 mg g^-1)calculated according to the Langmuir model fitting is 5 times that of the carboxylated cellulose fiber membrane,which is higher than most of the reported or commercial nanofiber or particle adsorbents.It is worth noting that for the dynamic adsorption of cationic dyes（membrane filtration）,driven by its own gravity,the flow rate of the solution through the HPF-C-S membrane（0.2 g）is as high as 530 L·m^-2·h^-1,which is88 times than that of the carboxylated fiber membrane(6 L·m^-2·h^-1);for the 2 mg L^-1BR46 and MB solutions,the volume of the solution to achieve 100%purification of the dye is as high as 4000 and 1500 m L respectively,which is fully in line with wastewater discharge environmental protection standards,showing absolute advantages over carboxylated cellulose fiber membranes that cannot completely purify dyes;the volume of pure water（20 L）produced per gram of HPF-C-S membrane is 3times of carboxylated cellulose fiber membrane filters（6 L）.