Isotactic Poly(ortho-Fluorostyrene): Synthesis, Mechanism, and Intramolecular F–H Locking Promoted Crystallinity and Solvent Resistance

A highly isotactic poly(ortho-fluorostyrene) (iPoFS) was successfully synthesized via coordination polymerization using a 2,2′-sulfur-bridged bis(phenolato) titanium dichloro complex. The resultant iPoFS exhibited a melting point up to 261 °C with exceptional crystallinity and high hydrophobicity and solvent resistance as well as superior mechanical properties (tensile strength of 60.4 MPa) over commercial syndiotactic polystyrene (sPS) and all other polar groups substituted polystyrenes. Isospecific oFS and St copolymers revealed tunable crystallinity and thermal properties depending on oFS/St composition, which containing ≥50 mol % oFS content exhibit melting points exceeding that of iPoFS, although isotactic polystyrene (iPS) sequences have slow crystallization rate and low crystallinity. NMR, DSC, and XRD analyses confirmed the isotactic configuration and crystalline nature of these (co)polymers. DFT calculations indicated that the fluorine substituent of oFS does not participate directly in the polymerization process but stabilizes the 31 helical conformation of iPoFS through intramolecular F–H interaction, thereby contributing enhanced crystallization and remarkable resistance to organic solvents. These findings demonstrate that the steric bulky ligand is crucial to isospecific selectivity and to prevent polar group coordination, while the intramolecular superinteraction endows polymer materials with unprecedented physical and mechanical performances.