Gas Permeation and Separation in Functionalized Polymers of Intrinsic Microporosity: A Combination of Molecular Simulations and Ab Initio Calculations

Abstract

We combine molecular simulations and ab initio calculations to investigate the permeation and separation of CO2/N2 in polymers of intrinsic microporosity (PIMs) with different functional groups (cyano, trifluoromethyl, phenylsulfone, and carboxyl). A robust equilibration protocol is proposed to construct model membranes with predicted densities very close to experimental data. The fractional free volumes (FFVs) in PIM-1 (with cyano), TFMPS-PIM (with both trifluoromethyl and phenylsulfone), and CX-PIM (with carboxyl) are 45.2%, 42.1%, and 38.7%, respectively. Hydrogen bonding is observed to form among carboxyl groups and contributes to the lowest FFV in CX-PIM. From wide-angle X-ray diffractions, the estimated d-spacing distances agree well with available experimental results, and the chain-to-chain distance in CX-PIM is the shortest among the three membranes. Ab initio calculations reveal that the interaction energies between the functional groups and CO2 decrease as carboxyl > phenylsulfone > cyano > trifluoromethyl; consistently, the simulated solubility coefficient of CO2 is the largest in CX-PIM. The simulated diffusion coefficient decreases with reducing FFV and correlates well with FFV. While the sorption selectivity of CO2/N2 increases in the order of PIM-1 < TFMPS-PIM < CX-PIM, the diffusion selectivity remains nearly constant; consequently, the permselectivity follows the same hierarchy as the solubility selectivity. This computational study provides microscopic insight into the role of functional groups in gas permeation and suggests that strong CO2-philic groups should be chosen to functionalize PIM membranes for high-efficiency CO2/N2 separation.

Chiral Polymers of Intrinsic Microporosity: Selective Membrane Permeation of Enantiomers

“…We conclude that permeation through the (+ +)-PIM-CN membrane is based on as elective diffusion-permeation mechanism. [27,28] Them odified material (+ +)-PIM-CN had aspecific rotation of a ½ 25 589nm ¼ + 378.38 8 in THF and exhibited aCDspectrum very similar to that of (+ +)-PIM-CN. [26] 1 HNMR, 13 CNMR, and IR spectroscopy (see Figures S6-S8) showed that hydrolysis proceeded to over 90 %c onversion into carboxylic acid groups without appreciable loss of molecular weight (M n = 67 578 gmol À1 and M w = 123 760;some broadening of the PDI occurred, to 1.8).…”

“…[33] (+ +)-PIM-CN can be chemically modified to expand the possible range of separation targets.T od emonstrate this possibility,weprepared acarboxylated derivative by subject-ing (+ +)-PIM-CN to acid hydrolysis to produce (+ +)-PIM-COOH (Scheme 1). [27,28] A decrease in the water contact angle of (+ +)-PIM-CN as compared to that of (+ +)-PIM-COOH from 1008 8 to 308 8 suggests that the (+ +)-PIM-COOH membrane is considerably more hydrophilic, aproperty that could be advantageous for the permeation of more-polar analytes (see Figure S9). According to the GPC results,the hydrolysis of (+ +)-PIM-CN with as trong acid was not destructive to the polymer backbone.…”

A highly rigid and gas selective methanopentacene-based polymer of intrinsic microporosity derived from Tröger's base polymerization

“…method was calculated to be 25.8 AE 0.5% which is slightly smaller than that of PIM-EA-TB (27.6%) 35 and of PIM-1 (28.8%). 36 The calculated fractional free volume conrms the poor polymer packing that is typical for all PIMs. The dihedral angle distribution for the MP structural unit observed within the packing simulation correlate well with the energy potential of deformation calculated by molecular dynamics (Fig.…”

Polymers of Intrinsic Microporosity

“…The application of packing simulation to understand and predict the performance of PIMs as gas separation membranes (see below) is also an active area of research [100][101][102]. However, it should be noted that, at present, simulations of PIM packing do not take into account polymer dynamics, which are important for the accurate prediction of gas diffusivities, nor do they give information on possible swelling effects due to gas adsorption.…”