Synthesis of Nitrogen-Heterocyclic Polypropylene Copolymer and Its Application in Blend Fiber

To enhance the thermal-oxidative stability of polypropylene (PP) fiber, several nitrogen-heterocyclic polypropylene copolymers were synthesized as blending modifiers, containing pyrrole (Py), indole (Id), and carbazole (Cz) groups. The large steric hindrance of indole and carbazole groups reduces the negative effect of heteroatoms on the catalytic center, with the highest polymerization activity of 2.33 × 10 4 kg polymer mol Zr −1 h −1 . Compared with PP, the 5% mass loss temperature ( T 5% ) of PPPy and PPId is increased, while only PPPy is capable of further delaying oxygen permeation. The steady-state shear curves indicate that the cross-linked structure between PPPy molecular chains inhibits the flow of PP/NHPP melt, while the indole and carbazole groups promote the flow of PP/NHPP melt. All PP/NHPP blends are successfully prepared into fibers. The mechanical properties of PP/PPPy fiber are well maintained due to the cross-linked structure. The thermo-oxidative stability of PP/NHPP fibers can be enhanced at a low blend content of 5 wt%, with the maximum rise of 13°C in T 5% and 10.7 min in oxidation induction time, which is expected to be applied in engineering fields requiring high-temperature stability. Highlights High polymerization activity of NHPP. NHPP was first incorporated for the melt-spun blend fiber. NHPP enhances the thermo-oxidative stability of blend fiber.