Due to its outstanding thermal stability, polyimide is often used to prepare carbon and graphite materials, such as highly crystalline graphite films, carbon nanofibers, nanoporous carbon films, carbon foams, etc. Therefore, it has broad application prospects and huge commercial value in many high-tech fields such as aerospace, aviation, space, microelectronics, precision machinery, and medical equipment.
Polyimide (PI) refers to a type of polymer containing an imide ring (-CO-NH-CO-) in the main chain. Polyimide has excellent properties. Aromatic polyimide materials have excellent high temperature resistance, low temperature resistance, high strength and high modulus, high creep resistance, high dimensional stability, low thermal expansion coefficient, high electrical insulation, low dielectric constant and loss, radiation resistance, corrosion resistance, etc. Advantages, at the same time, it has the characteristics of low vacuum volatile content and less volatile condensable materials. It can be processed into polyimide film, high temperature resistant engineering plastics, matrix resins for composite materials, high temperature resistant binders, fibers and foams, etc. Various material forms.
Polyimide resin, epoxy resin, and bismaleimide resin are considered to be the three major resin matrixes of carbon fiber reinforced resin-based structural composite materials, which are currently heat-resistant grades (long-term use temperature>300 ℃, short-term use temperature> 500 ℃) the highest resin matrix (epoxy resin: <200 ℃; bismaleimide resin: <250 ℃), the carbon fiber/polyimide resin composite prepared by combining with carbon fiber has light weight (specific gravity <1.8 g/cm3), high specific strength, high specific modulus, high temperature resistance, low temperature resistance, etc., have important application value in high-tech fields such as aerospace and aviation. However, due to the high rigidity of the chemical structure, polyimide resin has disadvantages such as insoluble and infusible, and difficult to process and shape; therefore, starting from the structural design of the material, by adjusting the chemical structure of the material, the material has both high Excellent comprehensive properties such as temperature resistance, high strength and toughness, as well as excellent molding process performance, have always been research hotspots in the field of polyimide resins.
Nowadays, high temperature resistant polyimide resin is roughly divided into three generations:
The first generation of polyimide resin matrix resistant to 316 ℃ (600 ℉) is a thermosetting PMR type polyimide resin, composed of aromatic diacid diesters, aromatic diamines and reactive end-capping agents at a low boiling point The solution resin with high solid content and low viscosity formed by reaction in alcohol solvent has excellent impregnation performance with various carbon fibers (T-300, T-700, C6000, IM5, UT500, etc.), and can prepare high-quality KH -304/Carbon fiber prepreg. KH-304/carbon fiber prepreg can be used to prepare high temperature resistant carbon fiber reinforced polyimide resin-based composite laminates or parts by using a reactive hot compression molding process or a reactive autoclave molding process.
The second-generation polyimide resin matrix resistant to 371 ℃ (700 ℉) was successfully developed with the support of the National "Ninth Five-Year Plan", mainly including KH-370 series products. model. KH-370 resin has excellent comprehensive properties. The standard solid content of the resin product is 50 ± 2%, the rotational viscosity at 25 ℃ is 200 ～ 250 mPa·s, the storage period at room temperature is 2 months, and it is at 0 ～ 4 ℃. 6 months. It has good impregnation performance with a variety of carbon fibers (T-300, T-700, C6000, IM5, U T500, etc.), and can be prepared into high-quality carbon fiber prepregs.
The third-generation polyimide resin matrix resistant to 426 ℃ (800 ℉) meets the urgent needs of composite materials for high temperature, high strength, and high toughness for aerospace and aerospace vehicles for supersonic, lightweight, and high mobility. On the basis of ℃ (700 ℉) polyimide resin matrix, the research and development of 426 ℉ (800℉) resistant matrix resin has been carried out in recent years, and satisfactory results have been obtained. The developed polyimide resin matrix (KH-400 series) resistant to 427 ℃ has good wettability to carbon fiber and can be made into high-quality carbon fiber prepreg (belt or cloth). The flexural modulus of the composite material at room temperature of the KH-400/carbon fiber laminate composite prepared by the reactive hot compression molding process is >1400MPa and the flexural modulus is >100GPa at room temperature; the flexural strength at 450 ℃ high temperature is >800MPa, bending Modulus>80GPa.
High temperature resistant polyimide materials are most likely to produce breakthroughs in the future due to their strong adjustability. Among them, ethynyl and phenylethynyl-terminated polyimide resins have been favored by researchers in recent years due to their good thermal stability, wide processing window, and no small molecule escape. It is hoped to develop higher temperature resistant polyimide resins. Polyimide resin and its composite materials.