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. 2022 Jan 14;12(1):91.
doi: 10.3390/membranes12010091.

New Membrane-Forming Aromatic Co-Poly(amide-imide)s: Influence of the Chemical Structure on the Morphological, Thermal and Transport Properties

Svetlana V Kononova  1 , Danila A Kuznetsov  1 , Galina N Gubanova  1 , Elena V Kruchinina  1 , Anatoly Ya Volkov  1 , Milana E Vylegzhanina  1 , Elena N Vlasova  1 , Boris Z Volchek  1
Affiliations

New Membrane-Forming Aromatic Co-Poly(amide-imide)s: Influence of the Chemical Structure on the Morphological, Thermal and Transport Properties

Svetlana V Kononova et al. Membranes (Basel). .

Abstract

Polymer film membranes are used to solve specific separation problems that dictate structural requirements. Structural and morphological parameters of film membranes based on glassy polyheteroarylenes can be controlled in the process of preparation from solutions that opens up prospects for obtaining structured membranes required for targeted separation. In the case of aromatic poly(amide-imide)s, the possibility of controlling film formation and structure virtually has not been studied. In the present work, a series of homologous co-poly(amide-imide)s differing in the number of repeating units with carboxyl-substituted aromatic fragments was synthesized by polycondensation. Comparative analysis of the processes of formation of membranes with different morphologies based on these polymers under equal conditions was performed. New information was obtained about the influence of the amounts of carboxyl groups and the residual solvent on structural properties of asymmetric membranes. The influence of these factors on transport properties of dense membranes under pervaporation conditions was studied. It was demonstrated that in the case of carboxyl-containing poly(amide-imide)s, the domains formed during film preparation had a significant effect on membrane properties.

Keywords: copolymers; dense and phase inversion membranes; pervaporation; poly(amide-imide); structure and morphology.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
AFM images of upper layers of nonporous dense PAI-1 (a,b) and PAI-2 (c,d) films ((a,c)—3D images, (b,d)—images obtained in the phase contrast mode) [8].
Figure 2
Figure 2
Structural formulas of PAI-1 (m = 1), PAI-2 (m = 0) and copolymers coPAI-1 (m = 0.7), coPAI-2 (m = 0.5), coPAI-3 (m = 0.3); letters are labels assigned to protons.
Figure 3
Figure 3
Portions of 1H NMR spectra of PAIs containing the signals attributed to CONH-groups (proton labels in Figure 2). (1) yellow—PAI-2, (2) violet—coPAI-3, (3) green—coPAI-2, (4) red—coPAI-1, (5) blue—PAI-1.
Figure 4
Figure 4
Diffraction patterns of coPAI-3 (curve 1), coPAI-2 (curve 2), and coPAI-1 (curve 3) with different ratios of PAI-1 and PAI-2 components.
Figure 5
Figure 5
AFM height images of film surfaces: coPAI-1 (a,b), coPAI-2 (c,d) and coPAI-3 (e,f). Scan matrix size—3 × 3 µm; (a,c,e) —the upper surface, (b,d,f)—the substrate-side surface.
Figure 5
Figure 5
AFM height images of film surfaces: coPAI-1 (a,b), coPAI-2 (c,d) and coPAI-3 (e,f). Scan matrix size—3 × 3 µm; (a,c,e) —the upper surface, (b,d,f)—the substrate-side surface.
Figure 6
Figure 6
AFM height image of surface of film coPAI-3; (a,b). (a)—the upper surface, (b)—the substrate-side surface. The inset in Figure 6b presents a contrast of lateral forces.
Figure 7
Figure 7
Diffraction patterns of the coPAI-2 membrane, taken from the side of the glance layer (1) and from the matte side (2).
Figure 8
Figure 8
SEM images of low-temperature fractures of asymmetric membranes PAI-1(0% DABA; a-1,a-2,a-3), coPAI-1(30% DABA; b-1,b-2,b-3), coPAI-2 (50% DABA; c-1,c-2,c-3), coPAI-3 (70% DABA; d-1,d-2,d-3), and PAI-2 (100% DABA; e-1,e-2,e-3). (a-1,b-1,c-1,d-1,e-1)—general cross-sectional view; (a-2,b-2,c-2,d-2,e-2)—top cross-sectional view; (a-3,b-3,c-3,d-3,e-3)—bottom cross-sectional view.
Figure 9
Figure 9
3D AFM images of surfaces of the coPAI-1 (a,b), coPAI-2 (c,d) and coPAI-3 (e,f) membranes; (a,c,e)—the upper surface, (b,d,f)—the substrate-side surface.
Figure 10
Figure 10
FTIR spectra of (a) PAI-2: (1) powder, (2) film, (3) asymmetric membrane; (b) PAI-1; (c) coPAI-2 (50% DABA): (1) asymmetric membrane, (2) film.
Figure 10
Figure 10
FTIR spectra of (a) PAI-2: (1) powder, (2) film, (3) asymmetric membrane; (b) PAI-1; (c) coPAI-2 (50% DABA): (1) asymmetric membrane, (2) film.
Figure 11
Figure 11
AFM images of the free (upper) surface of PAI-2 film (a,b); (a)—height image, (b)—phase contrast image.
Figure 12
Figure 12
Diagram (general view) of the permeability rate values (P [µm⋅kg⋅m−2⋅h−1]) of dense membranes (nonporous films) of the synthesized polymers PAI-1 (1,2), coPAI-1 (3,4), PAI-2 (5,6) in relation to penetrants of different polarities (Cyh—cyclohexane, EtOH—ethanol, MeOH—methanol, HOH—water). The mean values are shown, n ≥ 3. The order of penetrants during pervaporation: direction 1 (→ arrow on the diagram) Cyh → EtOH → MeOH → HOH; direction 2 (← arrow on the diagram) HOH → MeOH → EtOH → Cyh.
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