Preparation And Properties Of The PI/MWNTs Composites

Polyimides containing benzoxazole units are novel polyimides with highthermal stability. The rigidity of the benzoxazole ring makes the polymer better heatresistance and worse mechanical property. Carbon nanotubes have excellentmechanical, thermal and conductive properties and so on. Polyimide/carbonnanotube composite material can be prepared by introducing the functionalizedcarbon nanotubes into the polyimide matrix. At the same time, not only withoutsacrificing its thermal performance, but also improved the mechanical properties ofthe polyimide, thereby the overall performance of polybenzoxazole imide wasimproved.Chemical modification was used to modify multi-walled carbon nanotubes(MWNTs). After the purification, acidification, and amination, the surface of themulti-walled carbon nanotubes was grafted to the amino. And the functionalizedMWNTs was characterized by FTIR, Raman, XRD, XPS, SEM and other methods.The results showed that carbon nanotubes was successfully connected to the aminogroup, it can be well dispersed in the polar solvent.By two-step method, the polyimide copolymers were prepared with2-(aminophenyl benzoxazole)-5-ammonia and different structure of dianhydrides (PMDA,BPDA, ODPA,6FDA). The properties of different copolymers which were preparedwith different molar ratio of dianhydrides were investigated. The results showed thatrigid polyimide molecular chain can be flexible by introducing6FDA into thebackbone of polymer chains, thus the mechanical property was improved.Using in situ polymerization, the functionalized multi-walled carbon nanotubeswas evenly dispersed into the polybenzoxazole imide matrix by supersonic. Thus,the polyimide/MWNTs composite films were prepared. The properties of polyimidewith different amount of carbon nanotubes were studied. The results showed that theamount of multi-walled carbon nanotubes would not clearly affect the thermalproperty of polyimide/MWNTs composites. A small amount of multi-walled carbonnanotubes can improve the mechanical property of composite materials. When theamount of multi-walled carbon nanotubes exceeded1wt%, the mechanicalproperties of polyimide/MWNTs composites would decrease.