Synthesis Of UV-curable Polyimides And Preparation Of Aerogel Fibers

Polyimide aerogel is a kind of porous material,which has not only excellent mechanical properties and high temperature resistance of polyimide,but also excellent properties of aerogel,such as low density,high specific surface area and high porosity.It has a wide application prospect in aerospace,national defense and military industries.However,there are few studies on polyimide aerogel fibers at present,which is mainly due to the difficulty in the preparation and spinning technology of polyimide aerogel fibers,and the effective control of pore structure and fiber properties is difficult.Therefore,it is an urgent problem to seek suitable spinning technology to prepare polyimide aerogel fibers with good comprehensive properties.Ultraviolet(UV)curing technology has been widely studied for its advantages of low energy consumption,high efficiency,mild conditions and almost no volatile solvents.Photosensitive polyimide(PSPI)not only has excellent mechanical properties,heat resistance,chemical stability and so on,but also has photosensitive property.The photosensitive units in the polyimide molecular chain can form crosslinking network structure through photopolymerization and then improve the comprehensive properties of the material.At present,the preparation of aerogel(hydrogel)fibers is usually sol-forming state before spinning,which is difficult to realize gelation in the spinning process,resulting in high shrinkage rate of the final aerogel(hydrogel)fibers and poor mechanical properties.If UV curing technology is introduced,the polymer solution can be formed quickly after extrusion,and gelation in the spinning process can be realized.At the same time,it can simplify the process,and enhance the mechanical properties and structural stability of the fiber by the network structure formed by light crosslinking.Based on the above research background,low molecular weight photosensitive polyimide was first designed and synthesized in this paper,its curing formula and curing process were discussed,and the basic properties of cured films were analyzed.On the basis of the above polyimide,polyimide aerogel fibers with low molecular weight were prepared by wet spinning combined with UV light curing technology(photo curing-wet spinning).The spinnability of aerogel fibers and the influence of spinning technology on the properties of the fibers were investigated.At last,high molecular weight photosensitive polyimide was synthesized by controlled polymerization process,and combined with ambient pressure drying technology,polyimide aerogel fibers were prepared efficiently,and the aerogel fibers obtained had good comprehensive properties.The related research provides the experimental basis for the continuous and large-scale preparation of such aerogels.The main results are as follows:(1)Explore the structure design and curing process of PSPI.2,2-bis(3-amino-4-hydroxyphenyl)hexafluoro-propane(6FAP)containing phenolic hydroxyl as the carrier of photosensitive unit,the rigid benzimidazole unit to give the material good mechanical properties,and the end-group sealing technology was used to design and synthesize a soluble,low molecular weight polyimide with UV curing ability.The paper system explores the light distance,light electricity,light initiator species and content,reactive diluent kinds influence on curing forming process.And the light curing recipe and process conditions of polyimide is determined:light source,a distance of 10 cm;the electric flux of 100%;double(2 minus 2-trimethylbenzene formyl)-phenyl phosphine oxide(Irgacure 819)content to 3 wt%,and active diluent 1-vinyl-2-pyrrolidone(NVP)for 20 wt%,and the basic properties of the light curing film are analyzed.The tensile strength of the photocured film is up to 123 MPa,and the curing film with low wettability and water absorption.The thermal weight temperature of the curing film at 5%(T_d5)and 10%(T_d10)loss is 410°C and487°C,respectively.The results can provide a basis for the development of new photosensitive polyimide.(2)Study on spinnability of PSPI porous gel fibers.In order to improve the photocuring ability and curing efficiency of PSPI,on the basis of the original PSPI,polyethylene glycol diacrylate(PEGDA)with excellent photosensitivity was introduced to blend with the synthesized PSPI,and the spinnability of the system was studied in detail.The effects of PEGDA contents(C_PEGDA),extrusion rates(E_r)and spinneret diameters(S_d)on the morphology and basic properties of fibers were investigated.The structure showed that the optimized spinning solution formula and spinning process parameters were as follows:C_PEGDA=5 wt%;E_r=0.4 m L/min;S_d=0.4mm,under this condition,the internal structure of the fiber is relatively compact,the external appearance is cross-linked pore structure,density is 0.94 g/cm³,porosity is 21%,tensile strength is 2.2 MPa,with excellent bending flexibility and braided processing performance.(3)Efficient spinning of high molecular weight PSPI aerogel fibers and their structure and properties.In order to further improve the comprehensive properties of aerogel fibers,a high molecular weight photosensitive polyimide resin was synthesized by adjusting the polymerization process,and polyimide aerogel fibers were successfully prepared by the photo curing-wet spinning technology combined with ambient pressure drying technology.The structure,mechanical properties,heat resistance and heat insulation properties of the aerogel fibers were studied in detail.The results show that the aerogel fiber spun by high molecular weight PSPI has a specific surface area of 259 m²/g,a density of 0.23 g/cm³,and a porosity of 84%,showing good aerogel characteristics.The mechanical properties are greatly improved,and the tensile strength can reach48.7MPa.