Synthesis of Fluorinated Poly(phenyl-alkane)s of Intrinsic Microporosity by Regioselective Aldehyde (A2) + Aromatics (B2) Friedel–Crafts Polycondensation

The design of functionalized porous materials is an important research direction in material science, especially for fluorine-containing materials with enhanced thermal/oxidative stability, lower dielectric constants, and better gas-selective permeation. In this work, a series of poly(phenyl-alkane)s of intrinsic microporosity (PIM-xR) were synthesized by the methanesulfonic acid-catalyzed Friedel–Crafts hydroxyalkylation polycondensation of contorted and rigid multibenzene and benzaldehyde derivatives. The PIM-xR exhibited good thermal stability, excellent solution processability, and high Brunauer–Emmett–Teller (BET) surface areas (400–1200 m2 g–1). The physicochemical properties and applications of PIM-xR could be tuned by the type, quantity, distribution, and postmodification of substituents on the benzaldehyde derivatives. Unlike other contorted and rigid multibenzene derivatives, only electron-rich spirobiindane derivatives directly produced soluble, linear, high-molecular-weight polymers without cross-linking because spirobiindane possesses three t-butyl-like structural units that provide large steric hindrance at potential reactive sites. Subsequently, a series of fluorinated PIMs (PIM-xF) with different fluorine contents and distributions were explored, and the relationship between the microporosity of PIM-xR and degrees of rotational freedom of the polymer chains was analyzed using these PIM-xF. Flexible and transparent PIM-xF membranes were easily obtained by solution processing and exhibited high gas permeabilities and moderate permeability selectivity. In particular, the CO2/N2 separation performance of the PIM-5F membrane exceeded the 2008 Robeson’s upper bound (PCO2 = 3240 barrer and α(CO2/N2) = 27.9). This work provides a facile method for the precise design and preparation of fluorinated or other functionalized porous materials for environmental and energy applications.