Free Energy Profiles\nof Monomeric Species in MOFs\nfor Predicting Thermal Stability of MOF–Polymer Systems

Metal–organic frameworks (MOFs)\nand hybrid MOF–polymer\nsystems have been explored for gas separation applications. The pore\nsurface’s environment and interaction with different monomers\ncan help understand the physical properties of hybrid MOFs–polymer\nsystems. In our work, we have focused on understanding the interaction\nbetween the pores of UiO-66/UiO-67 and different monomeric species\nrepresentative of various polymers (ethyl methyl ether, poly(vinyl\nalcohol), polyvinyl chloride, and polypropylene), which are similar\nin structure but have different functional groups. We have used advanced\nsampling techniques to calculate the free energy profile of monomers\ntraversing through the pores. We find that the free energy barrier\nfor different monomers in UiO-66 and UiO-67 is very different and\ndepends on these monomers’ interaction with the pore environment.\nThe pore-limiting diameter of MOFs, the kinetic diameter of the monomers,\nand the free energy barrier of monomers traversing through the pores\nof UiO-66 and UiO-67 were used to understand the stability of these\nMOF–polymer hybrid systems. We find that UiO-66 with poly(vinyl\nalcohol), poly(vinyl chloride), and polypropylene is predicted to\nbe stable at room temperature compared to UiO-66 with ethyl methyl\nether. UiO-67 hybrid polymer systems are predicted to be unstable\nat room temperature.