Gas Transport Properties of Poly(trimethylsilylpropyne) and Ethylcellulose Filled with Different Molecular Weight Trimethylsilylsaccharides:  Impact on Fractional Free Volume and Chain Mobility

Polyimides (PIs) with single phenyl pendant substitution were prepared based on three diamines containing phenyl pendant group, namely, 2,5-bis(4-aminophenoxy) biphenyl, 2-phenyl-4,4′-diaminodiphenyl ether, and 2,5-diaminobiphenyl (p-PDA), with the dianhydride component of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride, respectively. The physical properties of the membranes were examined, including thermal properties, fractional free volume ( FFV), solubility, and morphological structures, and were compared with the analogues without phenyl pendant. Gas transport properties of the membranes were investigated and discussed from the viewpoint of structure–property relationship. For 6FDA-derived PI membranes, gas permeability increased as the degree of PI backbone rigidity leveled up. Gas transport properties were not improved by the incorporation of phenyl pendant group for 6FDA type containing ether linkage and marginally improved as compared between PI (6FDA/p-PDA) and PI (6FDA/p-phenylenediamine (PDA)). To increase the phenyl substitution density of 6FDA/PDA-type backbone, a novel diamine bearing two phenyl pendant groups, that is, 2,6-diphenyl-1,4-diaminobenzene (p, p′-PDA) was synthesized, and PI derived from 6FDA and p, p′-PDA was prepared. The gas permeability coefficients of PI (6FDA/p, p′-PDA) were remarkably larger than those of PI (6FDA/p-PDA) and PI (6FDA/PDA).

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Perfluoropolymer/Molecular Sieve Mixed-Matrix Membranes

Membranes ◽

10.3390/membranes9020019 ◽

2019 ◽

Vol 9 (2) ◽

pp. 19 ◽

Cited By ~ 4

Author(s):

Gianni Golemme ◽

Anna Santaniello

Keyword(s):

Transport Properties ◽

Molecular Sieves ◽

Gas Transport ◽

Maxwell Model ◽

Mixed Matrix Membranes ◽

Mixed Matrix ◽

Fractional Free Volume ◽

Phase Approach ◽

Gas Transport Properties ◽

Matrix Membranes

Despite the outstanding chemical, thermal and transport properties of amorphous and glassy perfluorinated polymers, only few works exist on the preparation and transport properties of perfluoropolymer/molecular sieves mixed-matrix membranes (MMMs), probably because of their poor compatibility. In this review, the compatibilization of ceramic molecular sieves with perfluorinated matrices is considered first, examining the effect of the surface treatment on the gas transport properties of the filler. Then the preparation of the defect-free hybrid membranes and their gas separation capabilities are described. Finally, recent modelling of the gas transport properties of the perfluoropolymer MMMs is reviewed. The systematic use of molecular sieves of different size and shape, either permeable or impermeable, and the calculation of the bulk transport properties of the molecular sieves—i.e., the unrestricted diffusion and permeability—allow to understand the nature of the physical phenomena at work in the MMMs, that is the larger the perfluoropolymer fractional free volume at the interface, and restricted diffusion at the molecular sieves. This knowledge led to the formulation of a new four-phase approach for the modelling of gas transport. The four-phase approach was implemented in the frame of the Maxwell model and also for the finite element simulation. The four-phase approach is a convenient representation of the transport in MMMs when more than one single interfacial effect is present.

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