Rational Design and Synthesis of Porous Polymer Networks: Toward High Surface Area

Head-on polymerization of tetrahedral monomers inherently imparts interconnected diamond cages to the resulting framework with each strut widely exposed. We have designed and synthesized a series of 3,3',5,5'-tetraethynylbiphenyl monomers, in which the two phenyl rings are progressively locked into a nearly perpendicular position by adding substituents of different size at 2, 2', 6, and 6' positions, as evident from single crystal structures. Computational simulation suggests that these monomers, though not perfectly regular tetrahedra, could still be self-polymerized into three-dimensional frameworks with the same topology. Indeed, five porous polymer networks (PPNs) have been successfully synthesized with these newly designed monomers through Cu(II)-promoted Eglinton homocoupling reaction. Among them, PPN-13 shows exceptionally high Brunauer-Emmett-Teller (BET) surface area of 3420 m(2)/g. The total hydrogen uptake is 52 mg/g at 40 bar and 77 K, and the total methane uptake is 179 mg/g at 65 bar and 298 K.