Direct Generation of Internally Functionalized Nanoporous Polymers: Design of Polymerizable Porogens

Control of porosity, pore size, pore connectivity, and pore functionalization are primary parameters that define the functionality and utility of porous polymers. A new approach to prepare highly crosslinked porous polymeric matrices, wherein the pore size and pore functionality are tunable, has been developed using a new design element, namely, polymerizable porogen. The polymerizable porogen (PolyPo) carries a styrenic unit and a pore-forming segment, namely, polyethylene glycol monomethyl ether (MPEG), that are linked via a thermally labile urethane linkage; upon nitroxyl-mediated controlled radical copolymerization of PolyPo with divinyl benzene (DVB), the MPEG segments microphase-separate to form interconnected nanodimensional domains. Solvothermal treatment of the crosslinked matrix, in alkaline aq-DMSO at 155 °C, leads to the near-quantitative transformation of the urethane linkage to amine groups that decorate the internal walls of the pores and, in the process, releases the pore-generating MPEG-OH into the solvent medium. We show that the pore size can be regulated by the length of the MEPG segment in the PolyPo, whereas the amine group density is controlled by the mole fraction of the PolyPo used for the preparation of the crosslinked matrix. The pore size increased from around 4 to 8 nm upon increasing the MPEG segment molecular weight from 350 to 2000 g/mol, while the BET surface area of the porous matrices fell in the range of 400 to 500 m2/g. Further, using PolyPos carrying styryl units at both ends, we showed that the pore size is governed primarily by the intervening PEG length and is unaffected by their difunctional nature. In summary, we demonstrate a new strategy to prepare porous crosslinked polymers with tailorable pore size; most importantly, the walls of the pores become directly lined with amine groups as a consequence of the solvothermal disconnection–hydrolysis of the urethane linkages.