A comparison of homopolymer and block copolymer structure in 6FDA-based polyimides

Abstract

Two homopolyimides and the corresponding block copolyimide, all based on the 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA), have been synthesized and fully atomistic models have been studied using molecular dynamics (MD) simulation. The respective diamines were 1,3-phenylenediamine (mPDA) and 2,3,5,6-tetramethyl-1,4-phenylenediamine (durene). These polyimides are potential candidates for gas separation applications. The synthesized polymers were processed as dense flat membranes. The effects of diamine structure were investigated at the molecular level and an attempt to compare the structural features of homo- and block copolyimides was made. Amorphous models were generated using a hybrid pivot Monte Carlo-MD sampling preparation technique. Average model densities were validated against experimental measurements on the dense films. Cohesive energies, Hildebrand solubility parameters, conformational characteristics, intermolecular interactions and available void spaces were analysed for each system. The durene diamine was found to hinder stacking and increase the available space. This is associated with the steric effect of the methyl substituents. In general, 6FDA-mPDA/durene exhibits an intermediate behaviour with respect to its base polyimides. For most of the examined properties, the differences between different size simulated systems were minor with the exception of the free volume distribution.

Experimental Mixed-Gas Permeability, Sorption and Diffusion of CO2-CH4 Mixtures in 6FDA-mPDA Polyimide Membrane: Unveiling the Effect of Competitive Sorption on Permeability Selectivity

“…Moreover, the density of 240-µm thick 6FDA-mPDA films aged for >3 months was identical to that of the fresh film samples. This value was slightly lower than other values reported in the literature—that is, 1.464 g/cm 3 [36], 1.46 g/cm 3 [37,38], 1.456 ± 0.014 g/cm 3 [28], and 1.45 ± 0.01 g/cm 3 [39], which were measured via the Archimedes’ principle procedure.…”

“…Similar to other commercial glassy polymers (e.g., polysulfones, cellulose acetates), polyimides have attracted the attention of the academic and industrial community for the following reasons: (i) strong thermal and mechanical properties (high glass transition and thermal decomposition temperatures, high ultimate tensile strength/elongation at break, and Young’s modulus) and (ii) excellent combination of pure-gas permeability and permeability selectivity [5]. In particular, polyimides based on the commercially available monomer 4,4′-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA) are typically solution processable and, therefore, suitable for hollow fibers spinning [5,28]. The polycondensation reaction of 6FDA with m-phenylenediamine (mPDA)—a commercially available monomer—yields the high-performance 6FDA-mPDA polyimide [29,30], shown in Figure 1.…”

Fluorinated copolyimide membranes for sour mixed‐gas upgrading

“…Copolymerization has shown to be a successful mean in this field. [23][24][25] Therefore, selected comonomers combined with 6FDA to form individual homopolymers with improved properties can be copolymerized together in an effort to prepare a new copolymer with simultaneous improved permeability and selectivity. As 6FpDA features desired high selectivity, several other 6FDA-based homopolymers feature high CO 2 permeability coefficient; one of them being 2,3,5,6-tetramethylbenzene-1,4-diamine (Durene).…”

“…In general, polymers with high selectivity can be combined with polymers with high permeability in an attempt to prepare new materials that capture both improved properties. Copolymerization has shown to be a successful mean in this field . Therefore, selected comonomers combined with 6FDA to form individual homopolymers with improved properties can be copolymerized together in an effort to prepare a new copolymer with simultaneous improved permeability and selectivity.…”

Revealing the High-Modulus Mechanism of Polyimide Films Prepared with 3,4′-ODA

“…Molecular dynamics (MD) simulations and Monte Carlo (MC) [ 15 , 16 , 17 ] techniques have been demonstrated to be highly consistent with experimental results. This technology has been utilized to investigate the various properties of PI [ 18 , 19 , 20 , 21 , 22 ]. For example, Lei et al [ 23 ] used this method to analyze the multilevel structure of some polyimide film systems.…”