Projet ANR-07-BLAN-0169 – CLICKMULTILAYER : layer-by-layer design of new films through click-chemistry
Programme : Blanc (BLANC) 2007
Année de financement : 2007
Coordinateur du projet : Monsieur CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ALSACE  (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ALSACE)
Partenaires : Centre national de la recherche scientifique; Institut national de la santé et de la recherche médicale; Université de Strasbourg
Montant : 385000.0 euros
Date de début : 2007
Durée : 36 mois
Résumé : "The alternate deposition of polyanions and polycations on solid surfaces leads to the formation of thin films called polyelectrolyte multilayers. The driving force of this layer-by-layer film buildup is the charge overcompensation that takes place during each polyelectrolyte deposition step. The cohesion of polyelectrolyte multilayers is usually attributed to electrostatic interactions even if hydrogen bonding and/or hydrophobic interactions can also play a role. In any case, the implied forces are of physical origin and are usually weak compared to covalent bonds. -  This layer-by-layer deposition process is very versatile and allows the functionalization of almost any type of surface, whatever its nature and geometry. Polyelectrolyte multilayers have received considerable attention over the last 10 years due to their widespread potential applications that range from implant coatings to filtration devices or specialized optical coatings. -  One of the weaknesses of such multilayer films built via non covalent interactions is their weak mechanical strength due to reversible nature of the forces involved in their cohesion. To overcome this problem several approaches that use covalent interactions for the layer buildup or to cross-link electrostatically assembled multilayers have already been proposed. The covalent layer-by-layer buildup processes described up to now took only place between polymers bearing a large density of reactive groups. -  In the present project we propose to extend the concept of polyelectrolyte layer-by-layer buildup process to a layer-by-layer buildup by covalent binding between polymers sparsely functionalized with reactive groups. This method should lead to a totally new family of well controlled architectures. To this end we propose to use a recently described very powerful coupling reaction belonging to the so-called ""click chemistry"". We will use here the reaction between an azide and an alkyne group. This reaction, which is Cu(I) catalyzed, proceeds under aqueous conditions, requires no activation step and is one of the most efficient among the click reactions. It should make it possible to dilute the ""click-reactive"" groups along the polymer chains as much as possible, allowing the rest of the monomers to be functionalized by other side-chains and the structure to gain in elasticity. -  The goal of our project is first to prove that our concept works, i.e. that films can effectively be constructed layer-by-layer with polymer chains bearing a small number of chemical groups. This will be investigated with neutral polymers (poly(N-hydroxypropylmethacrylamide)) and with polyelectrolytes (poly(acrylic acid)). For this to work, each deposition step must lead to an overcompensation of the number of active groups. This is an important issue. While it has been shown that an overcompensation of surface functionality of each newly deposited layer is possible in the case of polymers carrying one chemically reactive group at every or every second monomer repeat unit, no one has yet determined the maximum dilution of chemically reactive groups along the polymer backbone that still allows covalent layer-by-layer deposition. -  In the present project, we will, in particular, optimize the conditions for the click-chemistry reaction to take place on the surface of the film between the functional groups borne by the polymers and investigate the main parameters that influence such a buildup process: -  · What is the minimal group density that is required for the process to work? -  · Can the electrostatic repulsion between polyelectrolytes of same charge be overcome and a film be constructed with two polyelectrolytes of same charge? This could lead to films that are highly responsive to pH and/or ionic strength. -  · The azide and alkyne groups will be linked to the main chain through poly(ethylene glycol) linkers. What is the influence of the length of these linkers on the buildup process? -  This novel appro