Systems membranes - Combining the supramolecular and dynamic covalent polymers for gas-selective dynameric membranes

Article abstract of DOI:10.1039/c2cc33603k

The adequate selection of components makes possible the generation of double dynameric membranes, allowing the fine constitutional modulation of the gas transport performances.

Full text of DOI:10.1039/c2cc33603k

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COMMUNICATION
Systems membranes – combining the supramolecular and dynamic
covalent polymers for gas-selective dynameric membranesw
Gihane Nasr, Thomas Macron, Arnaud Gilles, Eddy Petit and Mihail Barboiu*
Received 18th May 2012, Accepted 3rd June 2012
DOI: 10.1039/c2cc33603k
The adequate selection of components makes possible the generation
of double dynameric membranes, allowing the fine constitutional
modulation of the gas transport performances.
Modular strategies for the fabrication of ultradense macroscopic
systems of addressable functional domains1 have been described
for molecular,2 hybrid3 or polymeric4 systems. Of special interest
is the generation of systems in which the diffusional solutes (ions,
water molecules or gas molecules) mutually interact within
directional transporting pathways. This offers the possibility to
use ‘‘Systems Membranes’’,3 the collection of objects (molecules,
polymers, nanoplatforms etc.), in order to generate the ‘‘fittest’’5
transporting systems via constitutional recognition.6 One may
conjecture that further development of such systems is related to
the molecular control of the transport functions. Low molecular
weight additives7 and free volume molecular polymers8 can be
used or tailored to prepare high-flux selective membranes. The
combination of permeable with hard segmented components
results in formation of segregated, well controlled micro-domains
with improved mass transfer functions.7c,9 The dynamic polymers
or dynamers,10 combining molecular and supramolecular features,
may give the possibility to achieve the molecular limit for the
construction of membranes of high diffusional behaviours.11
Metallodynameric11b and dynameric11a membranes can be used
to push the limit toward the molecular control of gas or ion
selective membranes. A further step consists of implementing this
strategy by using directional supramolecular and permeable
Fig. 1 (a) Synthesis of double dynameric membranes P1–P4 combining
supramolecular self-assembly via H-bonding of bisureido-dialdehyde, A,
and dynamic covalent imino-bonding with polyTHF, 1, polyPEG, 2,
polyPDMS, 3, and polyMePEG, 4, macromonomers.
dynamic covalent polymers. We report in this communication
such association between bisureido-dialdehyde supramolecular
polymers and dynamic covalent macromonomers, incorporating
both non-covalent H-bonds and reversible imino-covalent
connections (Fig. 1). The dialdehyde supramolecular connector A
and di(tri)amino-terminated macromonomeric building blocks
(i.e. bis(3-aminopropyl)-polytetrahydrofuran (Mn B 1100 g molÀ1),
tris[poly(propyleneglycol), amine-terminated] ether (Mn
B
3000 g molÀ1), polyMePEG 4) have been used to conceive
double dynameric membranes for gas separation. The dynameric
networks might be considered to contain linear (P1–P3) or
cross-linked star-type (P4) soft permeable domains combined
with hard supramolecular segments based on five structural
features:
polyTHF 1, bis(3-aminopropyl)-polyethyleneglycol (Mn
molÀ1), polyPEG 2, bis(3-aminopropyl)-poly-
B
1500
g
dimethyl-siloxane (Mn B 2500 g molÀ1), polyPDMS 3, and
Adaptive Supramolecular Nanosystems Group, Institut Europe´en des
`
Membranes – ENSCM-UMII-CNRS 5635, Place Eugene Bataillon,
CC 047, F-34095 Montpellier, Cedex 5, France.
E-mail: mihai.barboiu@iemm.univ-montp2.fr
w Electronic supplementary information (ESI) available: Experimental
details and characterisation data: NMR, XPRD, SEM, permeation
experiments. See DOI: 10.1039/c2cc33603k
(1) The bisureido-compound A forms supramolecular ribbons
in which the neighbouring ureas lie in the same plane with respect
to one another.6 Accordingly, arrays of layered stacks of A can be
generated, such that the bis-aldehyde moieties are disposed at the
extremities of each ribbon. Of particular interest is their potential
c
7398 Chem. Commun., 2012, 48, 7398–7400
This journal is The Royal Society of Chemistry 2012

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ability to generate hard uniform segments as directional fillers
in the membranes.12
(2) The hydrophobic polyTHF and the hydrophilic poly-
PEG linear macromonomers have been used to generate the
soft phases considered as permeables for the CO2 transport.
(3) The polyPDMS is among the most permeable polymers
known and present high permeability for gases.9
(4) The polyMe(PEG) star-type macromonomers allow a high
CO2 solubility and contribute to the cross-linking behaviour,
controlling the free volume of the dynameric network.13
(5) The polymeric environment might have a stabilizing
effect on the hydrolysis of the imine bond and the amine
exchanges during the membrane preparation.10
The 1H and 13C NMR, ESI-MS spectra of A are in agreement
with the proposed formulas.w The formation of the imine bonds
in P1–P4 is supported by the presence in the FTIR spectra of the
imine vibration shift at nCQN = 1605 cmÀ1 inside the aldehyde
vibration shift at nCQO = 1710 cmÀ1 initially observed for A.
The urea vibration band nCQO = 1700 cmÀ1 was downshifted to
1690 cmÀ1 in P1–P4 indicating the ureido ribbons formation.
Further insight into structural behaviours of P1–P4 is obtained
from the X-ray powder diffraction (XPRD). The XRPD patterns
of the polyTHF 1 and polyPEG 2, precursors and related
materials P1 and P2 present well-resolved peaks at 2y =
20–251 (d = 4.0–4.8 A), indicative of the close packing of the
crystallized PEG and THF chains with an ordered lamellar
morphology of periodic layers (Fig. S1, ESIw). Moreover, the
P2 dynamer displays a broad Bragg diffraction peak at 2y =
1.101 (d = 60 A), corresponding to the signature of long-range
crystalline architectures of 2. These domains appear only after
reaction with A, exhibiting dominant self-organization behaviour
and fixing the directional order over nanoscopic distances. Then,
supported thin-layer films were obtained by coating solutions
of P1 to P4 onto a planar polyacrylonitrile (PAN) support by
using the tape casting method. Scanning electron microscopy
(SEM) confirmed that the active layers (thickness of about
400 nm–2 mm) were dense without micropinholes with a
homogeneous structure at the nanometric scale (Fig. S2, ESIw).
Gas transport performances (i.e. permeability and selectivity)
through membranes are generally controlled by the gas-diffusivity
and by solubility-selective behaviours of materials. The pure gas
permeabilities for the P1–P4 membranes are shown in Table 1
and Fig. 2. As a general trend the dynameric membranes allow
high permeabilities for the CO2 and interesting CO2/light gas
selectivities. As expected, the most permeable membrane is P3,
with permeability and selectivity values in the range of those
previously reported for PDMS blends.7a In contrast, for the
crystalline polyPEG-based P2 membranes the CO2 permeability
and the CO2/N2 selectivity are strongly much lower than the
Fig. 2 (a) Pure gas permeabilities; (b) pure CO2/N2 selectivities at 30 1C
and 300–400 mbar, as a function of molar ratio %P4 = [P3]/[P4], mol/mol,
of macromolecular components.
estimated P = 143 Barrer and SCO /N = 48 performances of
2
2
amorphous PEG.9a The effect of structuration of the material is
clearly not beneficial for the diffusion of gas through the compact
low free volume P2 membrane. Despite the very low permeabilities
of both gases, the nice SO /N = 14.9 may be retained. In order
2
2
to compare the effect of self-organization induced via the
supramolecular bis-urea motif we prepared the dynameric films
P5 and P6 built from the macromonomers 1 and 4 connected via
isophthalaldehyde non-structuring cores. The effect of using soft
supramolecular fillers (A)n as directional components in dynameric
mixtures is related to the increased CO2 permeabilities and the
CO2/N2 selectivities (Table 1, compare P1 with P5 and P4 with P6).
This emphasizes the major advantage of using such soft segments
(A)n for tuning the diffusive domain morphology with enhanced
mass transport functions of gases by increasing the free volume of
the matrix, controlled mostly at the molecular scale.
Moreover, there are other opportunities toward this objective
and an increased free volume can also be obtained by the
incorporation of star-like macromonomers, 4 acting as a separator
of linear macromonomers 1–3. Generally, dynameric systems
are undergoing exchange, incorporation or decorporation of
their macromonomeric subunits linked together by reversible
interactions. This might play an important role in the ability to
more finely mutate their functional domains.10,11 Within this
context, we next considered that a combination of the beneficial
CO2 diffusive properties of P3 and the cross-linking properties and
the CO2/N2 selectivity of P4 would be interesting. These
experiments confirm that the CO2 transport through mixed
and dynamically exchanged polymeric blends P3/P4w is related
to two opposite effects: with increasing concentration of P3,
the rivalry between an increasing diffusivity of CO2 over the
polar polyPDMS chains of P3 versus the high cross-linking
Table 1 Pure gas permeabilities and selectivities of the P1–P6
dynameric membranes
Membrane PO , Barrer PN , Barrer PCO , Barrer SCO /N SO /N
2
2
2
2
2
2
2
P1
P2
P3
P4
P5
P6
6.2
2.2
0.2
204.8
1.6
3.0
80.2
3.00
2685.3
43.0
9.0
36.7
2.8
0.33
474.7
3.5
3.0
6.0
1.7
13.1
28
3
14
14.9
2.2
2.3
1
2.0
25.0
3
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 7398–7400 7399

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Fig. 3 Schematic representation of morphology of (a) block-copolymer
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in the initial permeability of P4 (Fig. 2a), while its selectivity is
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In conclusion, double dynameric membranes taking advantage
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domains can be rationally designed and synthesized for selective
separation of the CO2. The CO2 permeability and the selectivity
strongly increase when supramolecular bisureido-hard segments
(A)n such as reversible ribbon-type connectors are used instead of
isophthalaldehyde non-structuring core connectors. These ribbons
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2
2
are required.14
This work was conducted as part of DYNANO, PITN-
GA-2011-289033 (www.dynano.eu) and ANR 2010 BLAN
717 2 projects. We thank Wilfredo Yave for gas permeation
measurements.
Notes and references
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13 PEO-type rubbery materials exhibit very low permeability B12
Barrers due to their high crystallinity. PEG crystallinity can be
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3 M. Barboiu, Chem. Commun., 2010, 46, 7466–7476.
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7400 Chem. Commun., 2012, 48, 7398–7400
This journal is The Royal Society of Chemistry 2012