Angewandte
Chemie
Nanoporous Membranes Very Important Paper
Highly Ordered Nanoporous Films from Supramolecular Diblock
Copolymers with Hydrogen-Bonding Junctions
Damien Montarnal, Nicolas Delbosc, CØcile Chamignon, Marie-Alice Virolleaud,
Yingdong Luo, Craig J. Hawker, Eric Drockenmuller, and Julien Bernard*
Abstract: We designed efficient precursors that combine
complementary associative groups with exceptional binding
affinities and thiocarbonylthio moieties enabling precise
RAFT polymerization. Well defined PS and PMMA supra-
molecular polymers with molecular weights up to 30 kgmolÀ1
are synthesized and shown to form highly stable supramolec-
ular diblock copolymers (BCPs) when mixed, in non-polar
solvents or in the bulk. Hierarchical self-assembly of such
supramolecular BCPs by thermal annealing affords morphol-
ogies with excellent lateral order, comparable to features
expected from covalent diblock copolymer analogues. Simple
washing of the resulting materials with protic solvents disrupts
the supramolecular association and selectively dissolves one
polymer, affording a straightforward process for preparing
well-ordered nanoporous materials without resorting to cross-
linking or invasive chemical degradations.
prepare sensitive materials, such as biopolymers, low bandgap
polymers, or ionic conductors. In contrast to classical methods
requiring the degradation of sacrificial domains by invasive
techniques (e.g. UV irradiation,[8] reactive ion[9] or chemical
etching,[10] ozonolysis,[11] pyrolysis[12]) supramolecular cou-
pling driven by strong H-bonding interactions allows one
phase to be selectively dissolved by a solvent mixture with the
adequate balance of polarity and selectivity.
The design of supramolecular diblock copolymers capable
of assembly and high fidelity nanoscale pattern formation is
a complex challenge with dispersive forces driving the
incompatible homopolymers to phase separate on the macro-
scale. As a result, strong and directional binding interactions
are required to maintain the interfacial junction and confine
the phase separation to the scale of the polymer chains.
Theoretical models describe phase diagrams of such systems
by varying the segregation strength and the bond energy of
the junction.[13,14] Notable achievements have taken place in
this field since 2008[15–21] with strongly associating pairs, such
as ureiodopyrimidinone (Upy) and diamidonaphtyridine
(Napy), or guanosine and Napy groups, shown to promote
compatibilization[22] or nanostructuration[23,24] of immiscible
homopolymers. However, important bottlenecks remain to
extend the scope of supramolecular diblock copolymer
systems. The production of highly ordered morphologies
like those observed for well-defined covalent diblock copoly-
mers is still hampered by the difficulty to obtain quantitative
chain-end functionalization for high molar mass building
blocks (preparation of supramolecular block copolymers with
molecular weights above 20 kgmolÀ1 is indeed preferable to
enforce microphase separation). Also, high thermal stability
of the supramolecular complex is an essential requisite to
achieve long-range ordering by thermal annealing.
S
upramolecular assembly through non-covalent interactions
has become an essential tool in the design of smart[1,2] and
adaptive[3,4] materials, such as stimuli-responsive materials,
gels capable of molecular-recognition,[5] or self-healing net-
works.[6,7] Mimicking the self-assembly of conventional
diblock copolymers by hierarchical assembly of immiscible
homopolymers with reversibly binding chain ends offers
significant flexibility in the design and the processing of
nanostructured materials. The two immiscible components
can be prepared independently and are mixed without
resorting to chemical coupling. Furthermore, the possibility
to tune the strength of the supramolecular bond with various
stimuli (e.g. temperature or solvent) enables dynamic proper-
ties such as micro or macro phase transitions. Supramolecular-
mediated generation of ordered structures, such as nano-
porous materials, could also be simplified and applied to
Classic covalent PS-b-PMMA diblock copolymers (PS =
polystrene; PMMA = poly(methyl methacrylate)) have been
thoroughly studied over the last 20 years[25–27] (their self-
assembly in bulk and in thin films being an excellent model
system) and are still the preferred system for nanolithography
in the microelectronics and data-storage technologies. How-
ever, their relatively low Flory–Huggins parameter (c < 0.03)
requires high molecular weights for the copolymers to self-
assemble into ordered morphologies (Mn > 35 kgmolÀ1).
Precise synthesis and self-assembly of such supramolecular
analogues remain up-to-now untried and thus they constitute
an ideal system to investigate the potential of supramolecular
block copolymers.
[*] Dr. D. Montarnal, Dr. N. Delbosc, C. Chamignon,
Dr. M. A. Virolleaud, Prof. E. Drockenmuller, Dr. J. Bernard
Laboratoire d’IngØnierie des MatØriaux Polymres (UMR CNRS
5223) Institut National des Sciences AppliquØes (INSA-Lyon)—
UniversitØ Lyon 1
17 av. Jean Capelle, 69621 Villeurbanne (France)
E-mail: julien.bernard@insa-lyon.fr
Y. Luo, Prof. C. J. Hawker
Materials Research Laboratory, University of Santa Barbara (USA)
Supporting information for this article (synthesis and character-
ization of supramolecular RAFT agents and polymers by SEC and
1H NMR, study of the self-assembly in dilute solution (SEC, DOSY
NMR, ITC) and in the bulk (SAXS). Preparation of thin films and
porous membranes and their observation with AFM and TEM) is
To ideally mimic the self-assembly behavior of covalent
PS-b-PMMA block copolymers, we took inspiration from
Gong and co-workers (Figure 1),[28–30] who developed a re-
Angew. Chem. Int. Ed. 2015, 54, 11117 –11121
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
11117