Organic microporous materials offer a new approach to environmentally conscious and energy efficient gas storage and separation technology, such as O2/N2 separation, methane purification, and CO2 capture. This work utilizes molecular simulations to study novel nanoporous compounds, such as polymers of intrinsic microporosity (PIMs) and hypercrosslinked polymers (HCPs), in order to better understand their porosity and structure.
Generating simulated structures of amorphous polymeric materials is a non-trivial task, since unlike crystalline material, no reference structure is available. In this work, we present a general procedure for developing simulated structures of amorphous polymeric materials. The proposed structure generation procedure consists of three steps: (i) ab initio calculation of the repeat unit electrostatic charge distribution, (ii) construction of a periodic system by a simulated polymerization algorithm, and (iii) relaxation of the structure by a 21-step compression protocol.
The simulated “polymerization” is accomplished by connecting repeat units close together in the periodic box to construct either linear polymer chains or polymer networks. This procedure enables the system to be built at realistic densities while avoiding steric overlap issues typical of large, rigid repeat units, which is shown to be crucial for obtaining accurate simulated structures. The generality of the procedure is exemplified by application to a number of linear and network PIMs, including PIM-1 and HATN-PIM, as well as poly(dichloroxylene) and poly(arylene ethynylene) networks. All simulated samples are characterized by their structure and porosity with surface areas, pore size distributions, and structure factors. The results show good agreement with available experimental data.