Flow modification of GF/PA66 composites induced by anhydride-terminated branched fluorinated polyimide oligomer

An anhydride-terminated branched fluorinated polyimide oligomer (BFPI) was synthesized via a one-pot route from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 1,3-bis(4-aminophenoxy)benzene (TPER) and 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), using glacial acetic acid as the solvent and benzoic acid as the catalyst. The resulting BFPI exhibited a number-average molecular weight of 3.2×10³ g/mol and a viscous-flow temperature of 260℃. Owing to the presence of -CF₃ groups, BFPI possessed low surface energy and was thus prone to enrich at the glass fiber (GF)/ nylon 66 (PA66) interface. Meanwhile, its terminal anhydride groups could react with the hydroxyl groups on the GF surface and the terminal amino groups of PA66, thereby strengthening interfacial adhesion and promoting GF dispersion in the PA66 matrix. In the modification of a 40.0wt% GF-reinforced PA66 (GF/PA66) blend system with BFPI, compared to the unmodified system, the addition of 2.0wt% BFPI reduced the equilibrium torque of the blend by 63.3%. The resulting composite exhibited a 20.5% increase in tensile strength, a 31.5% increase in fracture energy, a 41.3℃ improvement in heat distortion temperature, a 12.0% reduction in water absorption, and only a 1.2% decrease in crystallinity. Morphological analysis of the composites using scanning electron microscopy and optical microscopy revealed that BFPI enabled a more homogeneous distribution of GF in the PA66 matrix, increased the retained fiber length from 139 μm to 235 μm, and reduced the fiber orientation angle along the melt-flow direction from 48.45° to 42.20°. Quantitative FT-IR analysis and amino end-group measurements further confirmed the compatibilization effect of BFPI. In comparison with the anhydride-terminated linear fluorinated polyimide oligomer (FPI), BFPI with a branched architecture delivered superior flow modification and more pronounced enhancements in the mechanical, thermal, and hydrophobic properties of GF/PA66 composites.