| Polyimide is a class of special engineering plastics with excellent resistance to heatstability and mechanical properties. Because of its excellent performance, Polymide iswidely used in the aerospace, energy, electronics and other fields. For the thermosettingpolyimide resin, due to its lower melt viscosity and the wide processing window, it issuitable for industrial processing that could also reduce the manufacturing cost of the mold.Phenylacetylene endcapped polyimide resins have wide processing windows andextreme outstanding thermo-oxidative stabilities after crosslinking reaction. In recent years,monomers for synthesizing polymer and processing study were been investigatd.Phenylethynyl capped polyimide-based resins, as PETI-5and Tria-PI, having excellentthermal properties, have too high melt viscosities and lack of the excellent workabilities,which are not suitable for low melt viscosity processing areas. PETI-5and Tria-PI canreduce their viscosities by adjusting the degree of polymerization and molecular weight,improving their processing properties. However, due to the relationship of the molecularweight and degree of polymerization, the decrease of the degree of polymerization wouldinevitably lead to the sharp decrease of the toughness of the material, the use of reducedperformance inevitably lead to the application of the material is restricted. Phenylacetyleneendcapped imide, as PETI-298, PETI-330and other small molecules oligomers, have lowmelt viscosities and wide processing windows. But poor thermal stabilities and mechanicalperformances are difficult to use in the resin matrix composite materials after curing.On the one hand, for the spacecraft in the process of high-speed flight, the structuralmember at the stagnation point at the working temperature can reach425℃. It should beconsidered for meeting the circumstances of the processing and the thermal performance ofthe resin; On the other hand, at this stage, it is also urgently needed for directly applying onthe production of low viscosity (η*<10Pa.s,200℃) and a wider processing window ofphenylacetylene capped imide resins. The case of resin can be greatly reduced manufacturing cost of the mold.We expect to obtain the phenylacetylene capped imide resin by introducing the etherlinkages, flexible ketone group in the molecular main chain and a nonlinear structure. Forthe good melt mobility, the oligomer is possible to meet the general injection molding needs.After completely crosslinking, the higher crosslink density can bring the material highexcellent thermal stability.Two new trifunctional phenylethynyl terminated imide oligomers, Oligo-pTPEPA andOligo-mTPEPA, were synthesized and characterized. two branch structure of thephenylacetylene endcapped oligomers have well solubility properties, wide processingwindows (η*<5Pa.s,250℃), and good thermal properties (Tg>410℃, Td5>520℃)after curd. In order to further application of the value of the resin, on the one hand, we usetwo phenylacetylene anhydride capped oligomer synthesized with the trifluoromethylaniline and dimethylaniline monomer synthesized as small molecule diluent to furtherreduce the melt viscosity of three-branch system by the method of blending (η*<3Pa.s,200℃). Due to the same phenylacetylene crosslinking of the crosslinked system, thediluents appear to reduce the melt viscosity of the oligomer system without the phaseseparation after completely crosslinked. As the results, the oligomers still maintain arelatively high thermal stabilities (Tg>300℃). On the other hand, we use the rigidstructure (containing an imidazole group) also containing phenylethynyl terminated imidegroups could further enhance the thermal stabilities and mechanical properties of thethree-branched blend system. The imidazolyl group benzene acetylene capped oligomer hasthe good thermal stability (Tg>520℃, Td5>560℃), while the low melt viscosity of theblend system can be maintained at a smaller molecular weight of imidazole oligomer part.For evaluation the processing performance of the resin, oligo-mTPEPA, the curingkinetics and gelation behavior are investigated and draw out guidance resin-basedcomposite materials production TTT-η phase diagram. We selected the oligo-mTPEPA asthe matrix resin of the carbon fiber composite material. We also tested of mechanicalproperties of the composites. The samples were evaluated for different aging time at177℃at air. For the composite material after aging at1000hours, the modulus decreased to acertain extent, a slight increase in strength and elongation. We analyzed by scanning electron microscope (SEM), the surface of the carbon fiber epoxy sizing agent wasdecomposed in the process of aging, which affected the adhesion of resin and fiber andexhibited certain characteristics of the resin. It would be the next work of the preparation ofhigh-performance composite materials to improve the properties. |
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