Synthesis Of Novel Polyimides And Study On Properties Of Polyimide-Epoxy Composite

Polyimide is a class of high-performance materials has a unique structure, is now widely used in high-tech fields. However, polyimide is difficult to dissolve and to melt lead to processing difficulties, its poor adhesion properties as well as the high cost of raw materials limiting a further application of the polyimide material. Epoxy material have good thermal, mechanical properties and excellent bonding, processing properties, but with the scope of application expand to the use of harsh environment field where traditional epoxy materials can not adapt to, study on high temperature resistance epoxy composites appear particularly important. Therefore the study of polyimide/epoxy composites, combining their advantages maks it have good processing properties and adhesive strength as well as high temperature performance to expand their range of applications having a larger value.In this study3-hydroxyacetophenone,4-chloronitrobenzene and4-hydroxybenzaldehy were firstly used as raw materials to synthesize novel phenolic hydroxyl-containing diamine4-(4-hydroxyphenyl)-2,6-bis[3-(4-aminophenoxy)phenyl]pyridine (m,p-HAPP) via Williamson reaction, modified Chichibabin reaction and Pd/C reduction reaction. The structure of the diamine wae confirmed by DSC, FT-IR,1H NMR and elemental analysis.Then novel reactive polyimides containing phenolic hydroxyl functionalities were prepared from4-(4-hydroxyphenyl)-2,6-bis[3-(4-aminophenoxy)phenyl]pyridine (m,p-HAPP) with four aromatic dianhydrides via one-step polycondensation procedure. The polyimides were obtained in almost quantitative yields with high inherent viscosities. FT-IR and’H-NMR spectra confirmed the formation of polyimides. No discernible peaks were observed in the XRD signals, which revealed their amorphous character. Almost all the polyimides exhibited good solubility in common organic solvents. The Tg values of the polyimides were all above220℃, all the polyimides exhibited good thermal stability with insignificant weight loss up to400℃in nitrogen, the residual weights of the polymers in nitrogen atmosphere at800℃were all above60%. The polyimide films possess tensile strength of86.92-94.68MPa, tensile modulus of1.86-2.05GPa, elongation at break of6.52-7.48%and water uptake of0.47-0.64%.Finally, polyimide derived from m,p-HAPP and ODPA along with epoxy resin were used to give a series of polyimide/epoxy composites. FT-IR and DSC method confirmed the composites were successfully prepared and cured completely. SEM cross-section tests showed that all composites had homogeneous structure, Plastic deformation of the material cross-section increases with the increase in PI content. Adding polyimide has a positive contribution to the composite Tg growth, With its increasing mass fraction the composite initial decomposition temperature and residual weight at800℃in nitrogen improved steadily. With the PI content increased from50%to90%the tensile strength of the materials rose from72.4MPa to89.6MPa, Tensile modulus went up from1.69GPa to2.02GPa, Elongation at break increased from4.9%to7.7%. The adhesive strength of the composite material experienced a peak of24.0MP with the polyimide content of29.9%, continue to increase the content of polyimide the adhesive strength of composite materials decrease to about20MPa, however, All the adhesive strength of composites were significantly higher than the one-component polyimide.