Synthesis And Properties Of Heat-resistant Polyimide Materials

Polyimide(PI),a kind of polymer material with high performance,has unique structural characteristics and excellent comprehensive properties.The functionalized PI films can be used in many fields,such as gas separation films,flexible optoelectronic device substrates,etc.With the rapid development of science and technology,there are higher requirements for the performance of PI films.Thermal properties make an important impact in many processes.PI with heterocyclic structure has strong rigidity,which makes it exhibit outstanding high temperature resistance.However,there are still a variety of problems to be solved.For instance,it is difficult to be dissolved by chemical reagent.On the basis of molecular design,five novel diamine monomers containing pyridine heterocycle were synthesized in this paper.At the same time,sulfone group was introduced into the monomer.A series of excellent polyimides were prepared by polycondensation with dianhydride monomer.The results show that the polyimide containing pyridine heterocycle has good thermal properties.The glass transition temperature(Tg)ranges from 276 ? to 363 ?.In the atmosphere of nitrogen,the 5 % thermogravimetric temperature ranges from 291 ?to 445 ?,the 10 % thermal weight loss temperature ranges from 389 ? to 472 ?,and the carbon residue rate at 800 ? is above 41 %.Among them,PI-3(6FDA/3b)has the most excellent comprehensive performance,it has good dissolving properties,it can be dissolved in DMF,DMAC,NMP and other polar solvents.Similarly,it also has good thermal properties,the Tg of the polyimide is 363?,5% thermal weight-loss temperature is 445? in the atmosphere of nitrogen.It also has the characteristics of low coefficient of thermal expansion,its coefficient of thermal expansion(CTE)is only4 ppm/?.Besides,it has some advantages in mechanical properties,the tensile strength approximated 103.9 MPa,elongation at break for 8.1%.In addition,it also has excellent optical transparency,the cut-off wavelength is 323 nm and the light transmittance can above 82% at a wavelength of 450 nm.PI-3(6FDA/3b)was copolymerized with ODA containing ether bond groups.By adjusting the molar ratio of diamine monomer 3b to ODA,the copolymerization with6 FDA resulted in different PI.The solubility of PI decreased slightly after copolymerization,at the same time,due to the introduction of flexible groups,the thermal properties also decreased,but the optical properties were improved.Moreover,with the increase of the content of diamine monomer 3b,the properties increased when the diamine monomer 3b: ODA= 9:1,the glass transition temperature can reach 355 ?,the 5 % thermogravimetric temperature up to 432 ?,furthermore,the transmittance is94 % at a wavelength of 450 nm,the maximum transmittance can reach 98 %.