Enhancing Processability of Phenylethynyl-terminated Imide Oligomers and Properties of Cured Polyimides via—CF3 Incorporation
摘要
Advanced aerospace technologies demand polymer-based wave-transparent materials with low dielectric constant(Dk),low dissipa-tion factor(Df),and high heat resistance for hypersonic vehicles.Thermosetting polyimides(Pls)from phenylethynyl-terminated imide(PETI)oligomers are promising candidates due to their excellent thermal stability;however,their application is limited by high Dk and Df at high fre-quencies and processing difficulties.Here,a series of PETI oligomers were designed and synthesized by polycondensation of 9,9-bis(3,4-dicar-boxyphenyl)fluorene dianhydride containing a Cardo structure,and six diamine monomers,respectively.The diamines were divided into three pairs by backbone flexibility,with each pair comprising a non-fluorinated diamine and its trifluoromethyl(—CF3)substituted analog.The effects of chain segment flexibility and-CF3 substitution on the processability of the oligomers and the properties of the cured Pls were systematically investigated.Results show that oligomers with-CF3 groups exhibit enhanced solubility and improved viscosity stability at 270℃ compared to their non-fluorinated counterparts.Moreover,the corresponding cured resins show lower Dk and Df values while maintaining good thermal sta-bility and mechanical properties.Notably,the BPAF-FA system exhibits favorable properties:an oligomer solubility of 40 wt％in NMP,and a mini-mum melt viscosity of 5.61 Pa.s;Dk=2.953,Df=0.0098(at 50％RH),Tg=403℃.Mechanistic analysis indicates that these improvements result from the synergistic effects of the intrinsic characteristics of-CF3 groups(steric hindrance,electron-withdrawing effect,low polarizability,and hy-drophobicity)and their role in influencing chain flexibility,symmetry,and molecular packing.These findings provide valuable guidance for the design of high-temperature-resistant,low-dielectric wave-transparent composite materials.
