Preparation and Properties of Phenylethynyl-terminated Polyimide Resins and Composites
A series of phenylethynyl-terminated polyimide prepolymers(Pre-1～Pre-5)with different molecular weights were synthesized in N-methyl pyrrolidone(NMP)by chemical imidization using m-phenylenediamine(m-PDA)and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride(6FDA)as the diamine and dianhydride monomers in the presence of 4-phenylethynyl phthalic anhydride(PEPA)as the end-capping agent.The structures and properties of these prepolymers were characterized and analyzed.The results showed that the prepared polyimide prepolymers had good melt fluidity in a certain range of molecular weights attributed to steric hindrance and twisted molecular structures,among which Pre-1 with the lowest molecular weight(calculated value of 1601 g/mol)exhibited the minimum melt viscosity of 3 Pa·s(316 ℃).The cured polyimide resins(PI-1～PI-5)displayed excellent thermal stability with 5％weight-loss temperature(T5％)of 532～536 ℃,10％weight-loss temperature(T10％)of 555～560 ℃ and the char yields at 850 ℃ of 54.3％～59.0％.The glass transition temperature(Tg:316～338 ℃)of these cured resins increased gradually with the decrease of molecular weights of prepolymers.The carbon-fiber-reinforced polyimide(CF/PI)composites were fabricated using PI-1 as matrix.The test results indicated that the composites obtained good interfacial combination and high heat resistance(T5％:574 ℃,T10％:648 ℃,Tg:359 ℃),as well as satisfactory mechanical properties with flexural strength of 753 MPa,flexural modulus of 54.0 GPa,interlaminar shear strength of 51.2 MPa and impact strength of 90 kJ/m2.
PolyimidePhenylethynylMolecular weight of prepolymerThermal propertyComposite
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