Pillar[5]arene Based Conjugated Microporous Polymers for Propane/Methane Separation through Host-Guest Complexation

Abstract

We present an efficient strategy for the preparation of conjugated microporous polymers incorporating pillar[5]arenes (P5-CMPs) with surface areas up to 400 m(2) g(-1) via Pd-catalyzed Sonogashira Hagihara cross-coupling reaction of triflate functionalized pillar[5]arene with 1,4-diethynylbenzene and 4,4'-diethyny1-1,1'-biphenyl linkers. In an effort to transfer intrinsic properties of pillar[5]arene, that is its ability to form strong host guest complexes with linear hydrocarbons in solution, into the solid-state, we investigated the affinity of P5-CMPs toward propane gas. Unlike previously reported porous solids, which showed isosteric heats of adsorption (Q(st)) for propane in the range of 32.9-36.9 kJ mol(-1) at zero coverage and increasing Q(st) with rising loading due to intermolecular interactions between propane molecules, we observed very high Q(st) values up to 53 kJ mol(-1) at zero coverage, which gradually decreased to similar to 35 kJ mol(-1) with increasing loadings. This observation indicates strong supramolecular host-guest complexation between propane and pillar[S]arene via multiple C-H/pi interactions, i.e., "macrocyclic effect" arising from the ideal size match of kinetic diameter of propane to the cavity of pillar[S]arene. This approach also allowed us to introduce thermodynamic selectivity for the separation of saturated hydrocarbons with low polarizability. High affinity of P5-CMPs for propane facilitated its efficient breakthrough separation from a simulated natural gas mixture (methane:propane, 9:1) at 298 K