Synergistic N-P coordination enables low-melting, high-crystallinity syndiotactic 1,2-polybutadiene via iron-based catalyst

Abstract

Syndiotactic 1,2-polybutadiene (SPB) is promising crystalline material with high wear resistance, yet its practical applications remain limited due to excessively high melting temperature (Tₘ), which hinder melt processing. In this study, we report a novel iron-based catalyst system, Fe(acac)₃/AIBN/PPh₃/AlR₃, that enables the synthesis of SPB with low melting temperature (T_m) (< 120 °C) and relatively high crystallinity (up to 18 %), thereby addressing a long-standing challenge. The catalyst design features a synergistic N-P coordination strategy: AIBN serves as the primary ligand, coordinating to the Fe center via cyano groups to modulate its electronic and steric environment, effectively lowering Tₘ while promoting syndiotactic monomer insertion. Meanwhile, PPh₃ functions as an auxiliary ligand, enhancing stereoselectivity by fine-tuning the coordination geometry through its strong σ-donating character. Comparative studies reveal that the presence of PPh₃ significantly improves the syndiotacticity and crystallinity of the resulting polymers without compromising catalytic activity. This work not only provides a simple and scalable catalyst platform for producing processable crystalline polybutadiene, but also offers new mechanistic insights into ligand field modulation for stereocontrol in Fe-catalyzed diene polymerizations, paving the way for future advances in tunable diene synthesis.