| A series of imide oligomers with low melt viscosity were synthesized in this subject. The synthesis was using a classical two-step method with2,3,3’,4’-biphenyltetracarboxylic(a-BPDA) as dianhydride and4-phenylethynylphthalic anhydride(4-PEPA) as a capping agent, together with two kinds of amines including1,3-bis(4-aminophenoxy)benzene(1,3,4-APB) and1,3-diaminobenzene(1,3-PDA). The preparation process of the imide oligomers were explored. The relations between structures and melt viscosity with different molar ratios of monomers was discussed. In addition, the influence factors of the thermal properties of the imide resins such as chemical structures and molecular weights were also discussed. The experimental results show that the melt viscosities of some imide oligomers were low enough and the process windows were wide for RTM. To the imide oligomers (PI-3) with a low molecular weight, the melt viscosity was low and the range of low viscosity was wide than others. With the increasing proportion of flexible structure in the main chain, the melt viscosity was also reduced. The cured resins exhibit high thermal degradation temperatures and glass transition temperatures (Tg). Increasing the amount of1,3,4-APB caused the decreasing of glass transition temperature while increasing the amount of the capping agent caused the increasing.Then, high temperature resin transfer molding (RTM) process was employed. The CF3031carbon fiber fabric reinforced polyimide composite laminates were successfully manufactured. The mechanical and thermal properties of the composites were characterized. DMA testing showed that the glass transition temperature was above300℃. The bending modulus under normal temperature was965MPa. The open hole compression strength was291MPa. The short beams shear properties was59MPa. The mechanical properties of the CF3031/PEPI composites reachs the most ordinary level of mechanical properties by RTMable resins for high temperature use. |
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