Molecular Simulations of PIM-1-like Polymers of Intrinsic Microporosity

Abstract

Polymers of intrinsic microporosity, or PIMs, are characterized by rigid and nonlinear or nonplanar backbones that inhibit space efficient packing, thus creating microporosity. PIM-1 has been well studied by both simulations and experiments and is compared in this work to two different PIM-1-like polymers, PIM-1c and PIM-1n. A detailed method for the generation of representative structures, including charge assignment from ab initio calculations, is presented along with simulated characterization of the pore size distributions, surface areas, structure factors, and methane adsorption isotherms. Simulated scattering for PIM-1c and PIM-1n show similar characteristic peaks as PIM-1, suggesting similar conformations. Adsorption isotherms of methane in PIM-1, PIM-1c, and PIM-1n were also predicted and compared to experimental data for PIM-1.

Application of computational methods to the design and characterisation of porous molecular materials

“…Furthermore, we have highlighted examples where these methods have been used for the a priori design and large scale screening of candidate PMMs. While many of these computational approaches have been employed to investigate porous framework and polymer materials, 60,79 the discrete composition and disconnected pores typical of PMMs has necessitated the development of novel methodologies. Salient examples are the analysis of dynamic pore interconnectivity 76 and the use of transition state theory to inspect the diffusion of large and constrained adsorbates.…”

“…This complication has led to the development of complex procedures which employ many molecular dynamics steps, often used in the production of glassy polymer structures. 55 Fortunately, unlike porous polymers, 60 achieving an equilibrated amorphous PMM system can be relatively straightforward owing to the smaller size and structural rigidity which affords fewer relevant degrees of freedom. Fig.…”

“…Notably, this compression step requires significant equilibration, >5 ns, and in some cases many annealing steps, 60 which can be computationally demanding. Thus accelerated simulations using graphical processor units (GPUs) have been employed in the application of this methodology to larger molecular structures.…”

Probing the Structural and Binding Mechanism Heterogeneity of Molecularly Imprinted Polymers

“…Whilst not leading to as rigid a system as in a real MIP, this approach extends beyond previous work. [15][16]23 Moreover, we believe that the imprints made in such a branched polymer are more optimal (as they are less rigid) and potentially more typical of imprints on external or macroporous regions of a polymer, where binding of analytes is more likely.…”

Polymers of Intrinsic Microporosity

“…Early work required the accurate experimental measurement of the density of the PIM, which is difficult to achieve as a film and almost impossible as a powder [97]. However, subsequent studies using a series of simulated high pressure compression and relaxation achieve a realistic packing without the need for density measurements [98,99]. Validation of the resulting packing structure was performed by comparison with X-ray scattering measurements on thin films of the polymer [96].…”