NAnostructured MAterials from Supramolecular block copolymers- Towards the Easy preparation of ordered nanoporous materials – NAMASTE

Multi-step syntheses afforded heterocomplementary stickers and the incorporation of RAFT chain transfer agents. Polymerizations in the presence of these chain transfer agents allowed for preparing well-defined macromolecules capable to interact strongly and generate supramolecular block copolymers. The interaction of the functionalized PS and PMMA blocks was further explored in solution (DOSY NMR, ITC, SEC) and in bulk (SAXS, AFM, TEM).

The first bottleneck which is the preparation of sticker-end functionalized polymers has been overcome and we have investigated the association of heterocomplementary functionalized PS and PMMA both in solution (NMR, SEC) and in bulk. Investigation on phase behaviour of our supramolecular block copolymers showed that morphologies similar to those expected for covalent analogues can be obtained. A procedure allowing for selective removal of PMMA domains through simple washing in polar conditions has been established leading to the preparation of nanoporous materials

Current efforts focus on the elaboration of rewritable surfaces using similar H-bonding species (collaboration with Pr Barner-Kowollik) and the preparation of hierarchically ordered microporous films using the so-called breath figure approach combined with the self-assembly of PS30k-SOA/PMMA15k-AOA (collaboration with Pr Billon)

Highly ordered nanoporous films from supramolecular diblock copolymers with H-bonding junctions Angew Chem Int Ed 2015. ASAP DOI: 10.1002/anie.201504838
Damien Montarnal, Nicolas Delbosc, Cécile Chamignon, Marie-Alice Virolleaud, Yingdong Luo, Craig J. Hawker, Eric Drockenmuller, Julien Bernard

This project addresses the development of smart nanostructured materials from AB supramolecular block copolymers generated from the H-bonding driven self-assembly of two homopolymers, PS and PMMA, that reversibly interact at terminal binding sites. A rational and optimal choice of elementary building blocks (i.e. homopolymer and H-bonding units chemical natures) and processing methods will allow the elaboration of nanostructured materials and nanoporous thin films, based on the strong, multidisciplinary and complementary expertise of the involved partners.
The generation of nanostructured materials from complementary H-bonded end-functional polymers has been scarcely addressed so far. Hitherto a major bottleneck stems from the fact that for all the associating systems previously explored, the driving force for phase separation is stronger than that for the formation of H-bonding supramolecular diblock copolymers. To overcome this key issue, the first aim of this project will consist in generating a library of well-defined polymers functionalized in a-position with heterocomplementary oligoamide strands (OS) specifically designed to form extremely stable six hydrogen bonds arrays (Kassoc ~ 10E9 M-1 in CDCl3 at 25 °C) that can however be easily disrupted upon addition of competing H-bonding polar solvents. Owing to the extremely high Kassoc exhibited by this pair of recognition units, we believe that under conditions that promote the formation of the H-bonding heteroduplex, the resulting supramolecular diblock copolymers will adopt morphologies observed in bulk or in thin films for traditional covalent block copolymers.
In order to promote the formation of nanostructured materials, the tailor-made preparation of well-defined homopolymers possessing very high degree of oligoamide functionalization will be performed using previously designed OS-functionalized RAFT chain transfer agents. Then, supramolecular diblock copolymers will be generated from well-defined heterocomplementary H-bonding PMMA and PS building blocks to establish reliable comparison with the phase separation of the extensively investigated PMMA-b-PS diblock system. The preparation of a library of oligoamide-based AB supramolecular diblock copolymers will provide a crucial insight into the influence of the blend composition, the molecular weight, and the processing conditions to obtain ordered phases (lamellar, hexagonal, spherical…) with a particular attention to the hexagonal phase.
The identification of the conditions leading to the formation of a long range order of hexagonally packed cylinders will be further exploited to generate H-bonding nanoporous materials with tunable pore size. A prerequisite will consist in applying experimental procedures (substrate surface neutralization) affording the formation of PMMA cylinders perpendicular to the substrate. The PMMA block will act as sacrificial phase to afford ordered nanoporous materials by removing PMMA nanodomains through simple washing in a polar and selective solvent of the PS matrix.
The envisioned results will constitute a major advance in the field of diblock copolymers, nanostructured and nanoporous thin films. Moreover the presence of H-bonding moieties at the surface of the pores would eventually allow for a reversible post-functionalization approach of the pores’ walls. This last aspect would substantially provide a strong interest of the targeted results in the broad community working in the field of nanostructured and nanoporous thin films.