Design And Synthesis Of Low Thermal Expansion Thermoplastic Polyimide Resin

Polyimide(PI)has excellent high and low temperature resistance,aging resistance,low dielectric loss and chemical stability and other performance characteristics.As a resin matrix,PI has important applications in the field of communication materials,such as optical transceiver,optical waveguide components,fiber connectors,cavity filters,etc.With the progress rapidly of photoelectric communication field,higher requirements are put forward for the performance of resin materials.The existing thermoplastic polyimide resin has the problem of high thermal expansion coefficient.Due to the mismatch of thermal expansion coefficient between various parts,there may be slippage and looseness between parts in the long-term use process.Therefore,the thermal expansion coefficient of thermoplastic resin should be reduced under the premise of keeping good machinability of thermoplastic resin.Based on the free volume theory,a series of thermoplastic polyimide resins were prepared by polyimide blending design,copolymerization design and adding inorganic fillers,and their structure and properties were characterized and analyzed.First,BPADA and PDA were used to prepare flexible resin system,and then BPDA and PDA were used to prepare rigid system.The two systems were blended at the stage of prepolymer polyamide acid to obtain A blend resin with molecular chain entwinding.The effects of blending ratio on the characteristic viscosity,wire size,thermal expansion coefficient and free volume of the mixed system were systematically studied.In the stage of prepolymer polyamide acid,the two systems are blended to make them have better compatibility.The rigid molecular chain is inserted into the flexible molecular chain,and the thermal expansion coefficient of the two systems is reduced when the molecular chains of the two systems are closely combined.The thermal expansion coefficient of the mixture system was reduced while the processing performance of the flexible system was retained.When the proportion of the rigid system was 30%,the thermal expansion coefficient of the blend resin system decreased from56.12ppm/K to 38.57ppm/K.A series of polyimide resins were prepared by using BPADA,BPDA,TFMB and PDA.The rheological properties,T_g,CTE and light transmittance of these resins were studied.The results show that the copolymer resins have low melt viscosity,and the melt viscosity of the fluorinated system is lower than104Pa·s in a large temperature range,which shows good processing performance.Copolymerized plexiglass has good high temperature resistance with the temperature between 230-250°C and 5%thermal decomposition temperature above 500°C.The thermal expansion coefficient of BPADA7/BPDA3-TFMB was 47.47 PPM/K by adjusting the ratio of each monomer.The cutoff wavelength of 150μm thick copolymer resin is 380-400nm,and the transmittance is more than 80%at 500nm.Bpada-tfmb system has the highest transmittance,reaching 87%at 500nm.The thermal expansion coefficient of BPADA7/BPDA3-TFMB copolymerized resin was further reduced by adding nano-alumina particles.The melt processing properties,dimensional stability and compatibility of nano-particles with resin matrix were studied.The results show that the PI resin modified by packing can meet the performance requirements of extrusion processing.The thermal expansion coefficient of BPADA7/BPDA3-TFMB decreased from 47.47 PPM/K to 39.26 PPM/K when the mass fraction of nanoparticles was 20%.The microstructure analysis of the resin showed that the particles in the modified resin dispersed evenly and bonded well with the resin matrix.