Preparation And Properties Of Organosilicon Modified Polyimide Functional Materials

Polyimide(PI),as a special engineering material,has excellent thermal stability,mechanical properties,dimensional stability and chemical stability.It is widely used in aerospace,solar cell floor,liquid crystal display and automobile manufacturing.However,the traditional PI materials still face many challenges,such as high water absorption(3%),lack of functional groups,difficult to dissolve and melt,poor adhesion to the substrate and so on.Organosilicon modified PI materials have attracted more and more attention due to their low moisture absorption,low dielectric constant and high low temperature resistance.In this paper,organosilicon structural units were introduced into the main chain of Polyimide by chemical modification.Two kinds of organosilicon modified PIA(PIA-APS,PIA-POSS-NH₂)were prepared,and the performance of two aerogel materials in adsorption performance was mainly studied.Two kinds of organosilicon modified PI film materials(PI-APS,PI-POSS-NH₂)were prepared by thermal amination method,and the materials were successfully endowed with high hydrophobicity and optical transparency.On the basis of polyimide film modified by silicone,MWCNTs/PI composite film was prepared by introducing MWCNTs into polyimide substrate.MWCNTs/PI composite film not only gives the material certain conductivity,but also greatly improves its mechanical properties.The details were as follows:1.Octa(aminopropylsilsesquioxane)(POSS-NH₂)was synthesized by using3-aminopropyltriethoxysilane as monomer in the presence of hydrochloric acid.The structure of POSS-NH₂ was characterized by FTIR,¹H NMR and XRD.Siloxane monomer(1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane(APS)and POSS-NH₂)were copolymerized with 3,3',4,4'-benzophenone tetracarboxylic dianhydride(BTDA),4,4'-diaminodiphenyl(ODA),and two kinds of organosilicon modified PIA were prepared by simple thermal curing and atmospheric drying process.The results of FTIR and solid¹H NMR indicate that the-Si-O-Si-structural unit is successfully introduced into the PIA network.SEM and BET confirmed that the introduction of silicone structural units could form a larger pore structure inside aerogels,thereby enhancing the adsorption performance of aerogels.The modified aerogel material has high hydrophobicity,and the maximum contact angle(CA)with water can reach 143°degrees.In the oil-water mixture,the selective adsorption of oil can be achieved effectively.Aerogel materials showed good cyclic adsorption capacity for various organic solvents such as acetone,methanol and ethyl acetate.After 15 adsorption experiments,the adsorption capacity of aerogels(almost 3 times their own weight)almost remained unchanged.The results showed that silicone modified PIA could be used as an adsorbent in the field of wastewater treatment to achieve selective adsorption of oil pollutants and harmful organic reagents.2.Polyimide precursor polyamic acid(PAA)was prepared by terpolymerization of3,3',4,4'-benzophenone tetracarboxylic dianhydride(BTDA),4,4'-diaminodiphenyl(ODA)and siloxane monomers(APS,POSS-NH₂).Two groups of silicone modified PI films with different formulations were prepared by scraping and thermal amination.FTIR results show that the organosilicon structure unit has been successfully introduced into the main chain of PI,and the copolymer has high elongation at break.Because the flexible segment of silicone is more conducive to the micro movement and deformation of molecular chain,the ductility or toughness of the film material is significantly improved.However,the increase of the free volume of the system will weaken the intermolecular interaction,which will reduce the tensile strength of the film.The highest static contact angle(CA)is 100°and compared with pure PI film(contact angle is 63°),which shows that the hydrophobicity of the material can be improved by silicone modification.The results show that the silicone modified PI film has better optical transparency.The dielectric property test shows that the existence of flexible-si-o-si-segment can reduce the dielectric constant of the material.TGA test results show that the thermal stability of PI decreases with the introduction of organosilicon structural units,and the main reason for the decrease of thermal stability is due to the thermal degradation of Si-C bond with lower dissociation energy.3.The ternary copolymerization of 3,3',4,4'-benzophenone tetracarboxylic dianhydride(BTDA),4,4'-diaminodiphenyl(ODA)and POSS-NH₂ was carried out at room temperature.Meanwhile,multi walled carbon nanotubes(MWCNTs)were introduced into the reaction system.Finally,MWCNTs/PI conductive composite films were prepared by scraping and thermal amination.The mechanical properties of MWCNTs/PI conductive composite film show that the tensile strength of MWCNTs/PI conductive composite film can reach more than 130 MPa,and its strength is significantly improved compared with polyimide without MWCNTs reinforcement.The contact angle of the composite film can reach 110°under the combined action of POSS-NH₂ and MWCNTs,which can be used as a high hydrophobic film material.MWCNTs are uniformly dispersed in the polyimide substrate,forming a conductive network in the copolymer,and the conductivity of the material increases with the increase of MWCNTs content.In addition,MWCNTs/PI conductive composite can transform the morphological changes(including folding and twisting)of the material itself captured by MWCNTs/PI conductive composite into the changes of potential signal,which indicates that MWCNTs/PI conductive composite film can be used as a sensor with broad application prospects.