Fluorine-Modulated Reactivity Enables One-Pot Kinetic Sequence Programming of Block Copolyesters

Monomer sequence strongly influences copolymer properties, but direct block formation from a monomer mixture requires a large reactivity contrast. Here, fluorination was used to regulate anhydride reactivity in the cesium pivalate-catalyzed ring-opening alternating copolymerization (ROAC) of tetrafluorophthalic anhydride (FPA), phthalic anhydride (PA), and 3-perfluorohexyl-1,2-epoxypropane (PFE). Time-resolved nuclear magnetic resonance (NMR) spectroscopy showed that FPA reached >99% conversion before detectable PA incorporation. With 1,4-benzenedimethanol as a bidirectional initiator, this sequential consumption generated a central poly(FPA-alt-PFE) segment followed by poly(PA-alt-PFE) growth from both chain ends. Molar mass evolution, end-group analysis, and diffusion-ordered spectroscopy (DOSY) NMR collectively supported covalent block formation. Sequential incorporation was retained across three different FPA:PA feed ratios, and Beckingham-Sanoja-Lynd analysis yielded large and reciprocal effective reactivity-ratio descriptors (rFPA≈8.3-8.6×102 and rPA≈1.2×10-3), consistent with the experimentally observed real-block regime. Matched model reactions further indicated faster FPA ring-opening and higher observed epoxide-opening reactivity in a fluorinated aromatic carboxylate model system. These results demonstrate that H-to-F substitution can provide the kinetic bias required to program block copolyester sequence within a single ROAC platform.