Preparation And Properties Of Semi-interpenetrating Polyimide Networks

The thermal-setting polyimide have excellent processing properties and thermalstability but poor toughness. Its heat resistance have improved by introducing thebenzoxazole units into the polyimide matrix. But its toughness is worse. Instead,thermal-plastic polyimides with better toughness are mixed with the thermal-settingpolyimides into the semi-interpenetrating polyimide networks which contains theadvantages of these two kinds of polyimides and has better toughness and heatresistance. These above shows a huge potential for industrial application.4-phenylethynylphthalic anhydride (4-PEPA) was synthesized by the palladium/copper catalyzed Sonogashira coupling reaction between phenylacetylene and4-bromophthalic anhydride. The traditional preparation method of4-PEPA wasimproved and the reaction conditions was optimized, which enhanced the productivityand purity of4-PEPA. The structure evolution was characterized by XRD, IR, UV-vis,NMR and other methods, the purity characterized by HPLC and the thermal propertywas characterized by integrated thermal analyzer. The results showed that4-PEPA canbe used as the end-capped monomer of thermal-setting polyimides.The polyimide oligomers were prepared by diamine with benzoxazole， differentstructure of dianhydrides and4-PEPA. Its structure and thermal properties werecharacterized by IR and DSC, respectively. Its crosslinked curing temperature was alsoinvestigated. By crosslinked curing reaction using the oligomer, the thermal-settingpolyimide was prepared with different structure and different molar ratio ofdianhydrides. IR analysis showed crosslinked curing reaction happened completelywithout the adsorption peak of alkynyl. The result of TG and DSC show that thethermal-setting polyimide have an excellent heat resistance property and completecrosslinked curing reaction.The different ratio of semi-interpenetrating polyimide networks film was preparedby mixing the thermal-setting precursor with the thermal-plastic one. Then its structure,morphology, thermal performance and mechanical property were characterized. Theresults showed that semi-interpenetrating polyimide networks with50wt%thermal-setting polyimide exhibited excellent thermal and mechanical properties andcould be applied to the industry.