Study On Structure Modulated Design And Composites Of Alkyne-Containing Polyimide

As a high-performance resin,polyimide can produce films,adhesives and advanced composite materials with its many advantages,and has become an indispensable material in the fields of aerospace,microelectronics and military weapons.With the rapid development of high-tech field,the requirements of resin strength at higher temperature,the restrictions of bonding conditions,the resistance to extreme environment and the heat accumulation caused by the high concentration of microelectronic devices are many problems to be further solved and improved.This thesis aims to improve the heat resistance and adhesive ability of polyimide,and to design the structure of acetylene-containing polyimide for the preparation of cross-linkable thermoplastic polyimide resin and acetylene-terminated polyimide oligomers.Furthermore,through compounding and in-situ polymerization to obtain high temperature resistant and high strength of polyimide co-blended modified adhesives and high thermal conductivity polyimide composite films.The main research contents and results are as follows:A series of alkynyl-containing thermoplastic homopolyimides(Hm-PI)were synthesized based on 4,4’-(ethyne-1,2-diyl)diphthalic anhydride(EBPA)and different diamine monomers,which were tested for thermal properties,thermal stability,mechanical and adhesive properties.The results show that Hm-PI not only has good film-forming properties,but also exhibits excellent mechanical properties.The mechanical properties are significantly affected by the different diamine structures,and the tensile strength is 126.6-252.9 MPa,Young’s modulus up to 7.28 GPa,and elongation at break up to 11.90%.The initial decomposition temperatures of Hm-PI-1 after high-temperature thermal cross-linking can reach 551℃and547℃under nitrogen and air atmosphere,respectively.The optimum improvement of adhesion strength before and after heat treatment was achieved at 350℃and 400℃,indicating that the high-temperature thermal cross-linking of the acetylene group in the main chain is beneficial for maintaining the thermal stability of the resin and improving the high-temperature adhesion strength,which provides theoretical support for the subsequent modification work.In order to overcome the problem of losing toughness and embrittlement caused by excessive cross-linking of acetylene groups,relatively flexible 4,4’-oxybisphthalic anhydride(ODPA)was used to partially replace EBPA monomer to synthesize different ratios of acetylene-containing thermoplastic copolyimide(Co-PI).The glass transition temperature(T_g)and mechanical properties of Co-PI were improved with the increased copolymerization ratio of alkyne-containing monomers,while its thermal stability and thermal degradation resistance were also significantly improved.The T_g of Co-PI was increased from 263-270°C to291-387°C before and after cross-linking by comprehensive comparison,respectively.Acetylene group cross-linked not only played a dominant role in the growth of T_g,but also the thermal stability was effectively maintained and enhanced.The mechanical and adhesive properties of Co-PI can be greatly improved by the appropriate amount of acetylene-based crosslinking,in which the tensile strength and tensile modulus of Co-PI-4 after cross-linking are significantly increased by 86.68%and 205.30%compared with those of Co-PI-O,and the adhesion strength can reach more than 8 MPa at 350℃and exceed 6 MPa at 400℃.Overall Co-PI-4 has a high-T_g,excellent temperature resistance and adhesive properties,which are essential for the development of high temperature resistant adhesives.In order to solve the issue of inferior processing performance of thermoplastic polyimides.A series of APA capped polyimides at three degrees of polymerization were synthesized by using m-aminophenyl acetylene(APA)as a capping agent and modulating seven combinations of four diamines and four dianhydride monomers.To investigate the effect of structural changes of acetylene-terminated polyimides on heat resistance and adhesive properties.It was found that the dianhydride monomer structure has greater effect on the T_g of APA-terminated polyimide,and the thermal stability performance will be improved to different extents with the increase of the polymerization degree of the oligomers,among which B-PI and PI-O have better thermal stability.On the whole,PI-O-1 with flexible phenyl ether structure has the best adhesive performance,with high temperature adhesive strengths up to 11.75 MPa and 8.56 MPa at 350°C and 400°C,respectively.The results provide the basic parameters for studying APA-terminated polyimide adhesives.For preparing high-temperature resistant and high-strength polyimide resin adhesives,two types of thermosetting polyimides(SPO and BSP)were co-polymerized by regulating the ratio of mutually heterogeneous ODA and BPDA monomers.Two kinds of isomeric polyimides have good thermal stability after curing,which the introduction of appropriate amount of isomeric units can effectively improve the adhesion strength.SPO-2 exhibited more excellent adhesive performance,and the room temperature adhesion strength can be enhanced 71.15%.Polyimide co-blended modified adhesive(SPO-2/Co-PI-4)was prepared by isomeric SPO resin with thermoplastic Co-PI resin.The investigation shown that SPO-2/Co-PI-4 not only has relatively low curing temperature and requires small pressure,but also has a long storage time.The adhesion strength of SPO-2/Co-PI-4 can exceed 11 MPa at both 350℃and 400℃.It can be used at 200℃for a long time,300℃for a short time and400℃for an instant.Its excellent comprehensive properties make SPO-2/Co-PI-4 have broad application prospects in the field of high temperature resistant resin adhesives.In order to prepare polyimide films with both high temperature resistance and high thermal conductivity,carbon nanotubes/silver nanowires composites(CA)were prepared by in-situ reduction method.A series of polyimide/carbon nanotube/silver nanowire composite films(CA-PI)were prepared by in-situ polymerization of CA into high temperature resistant copolyimide matrix.The T_g,thermal stability and mechanical properties of CA-PI can be effectively improved by the synergistic effect between the less addition and high dispersion CA reinforced phase and resin matrix.CA-PI-3.0 can improve the thermal conductivity by158.23%compared with Co-PI.CA-PI can provide a new strategy for expanding the application field of high temperature resistant polyimide due to its excellent comprehensive performance.