MorphologicAl Control of self-Assembled amphiphilic block cOpolymers through Stimuli – MACAOS

MACAOs is a fundamental research project of PRC type that gathers three teams with complementary research skills in the fields of amphiphilic block copolymer synthesis and the use of their self-assemblies in aqueous solution and at liquid-liquid interfaces. The goal of MACAOs is to synthesize and investigate a series of amphiphilic block copolymers with bottlebrush hydrophobic blocks and an over whole tadpole structure. Such a bottlebrush structure is required for constraining the packing parameter of the self-assemblies and having a flat curvature as a result to induce anisotropic structures. Hydrophobic blocks will be also tempered by incorporating hydrophilic pH-sensitive units in order to decrease their surface tension in order obtaining self-assemblies at equilibrium that can commute reversibly upon applying external trigger. The same pH-sensitive units will also be constitutive of the hydrophilic block linked to a single or two bottle brush tempered hydrophobic blocks for obtaining a series of amphiphilic di and triblock copolymers. The synthesis of copolymers will proceed through a combination of controlled radical polymerization techniques (nitroxide and Copper(0)-metal mediated ones) varying several structural parameters (sizes of the blocks and size of the polymer chain of the bottle brush block). The targets in terms of chemistry will rely on results obtained within the consortium on homologous linear di and triblock amphiphilic copolymers. Once dispersed in water, the bottlebrush tadpole polymers are expected to self-assemble within polymeric worm-like micelles at thermodynamic equilibrium which will constitute a major step forward the state of the art which most often reports the formation of anisotropic frozen nanoparticles when processing block copolymers. Upon ionization of pH-sensitive units, a reversible tuning of both the structure (length and aggregation number) and dynamics (scission/recombination and reptation times as well as the exchange time of single polymer chains between the micelle and the solution) of the self-assemblies will occur. We will valorize the properties of such smart self-assemblies by achieving smart hydrogels at relatively low concentration through the entanglement of the polymeric worm-like micelles. Such hydrogels will display self-healing properties that will be investigated and the dynamics of the self-assemblies is expected to progressively fasten with the ionization degrre until the occurrence of a “degelation” transition at high ionization degree due to a reversible disrupt of the self-assemblies. Owing to their amphiphilic nature, the bottlebrush tadpole block copolymers will adsorb at liquid interfaces and will have the ability to stabilize emulsions. Their pH-sensitive character will also confer pH-sensitivity to the prepared emulsions. Moreover, the systems synthesized in the frame of MACAOs will offer a unique opportunity to easily tune the adsorption kinetics and the stabilizer size by varying the ionization and thus to tune the adsorption/desorption energy. Such a possibility makes it possible to progressively evolve from surfactant-like stabilizers to particle-stabilizers leading to so called Pickering emulsions. In the latter case, 2D elasticity of the interface is likely to occur with a low amount of stabilizers thanks to an easy percolation of anisotropic self-assemblies. The challenging objective of MACAOs can be summarized as driving amphiphilic block copolymers to self-assemble into smart anisotropic nanostructures at equilibrium that can commute reversibly into isotropic ones through an external trigger and taking benefit of it in terms for interfacial and aqueous bulk properties. It should be added that MACAOs will focus on pH as a trigger but we are pretty confident in the fact that our concept can be transposed to other types of triggers.