Elaboration of well-defined "Rasta" resins and their use as supported catalytic systems for Atom Transfer Radical Polymerization (ATRP)
Résumé
New supported catalytic systems based on the immobilization of a ligand onto supported (co)polymers were prepared, allowing copper immobilization onto a solid support during the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). These supported catalysts were elaborated by the ATRP of 2-vinyl-4,4-dimethyl-5-oxazolone and/or styrene onto a Wang resin initiator. Two different approaches were used, involving well-defined architectures synthesized by ATRP. First, a supported electrophilic homopolymer [Wang-g-poly(2-vinyl-4,4-dimethyl-5-oxazolone)] was synthesized to obtain an azlactone ring at each repetitive unit, and a supported statistical copolymer [Wang-g-poly(2-vinyl-4,4-dimethyl-5-oxazolone-stat-styrene)] was synthesized to introduce a distance between the azlactone rings. The azlactone-based (co)polymers were then modified by a reaction with N,N,N′,N′-tetraethyldiethylenetriamine (TEDETA) to create supported complexing sites for copper bromide. The ATRP of MMA was studied with these supported ligands, and a first-order kinetic plot was obtained, but high polydispersity indices of the obtained poly(methyl methacrylate) were observed (polydispersity index > 2). On the other hand, the supported ATRP of styrene was performed, followed by the nucleophilic substitution of bromine by TEDETA (Wang-g-polystyrene–N,N,N′,N′-tetraethyldiethylenetriamine) at the chain end of the grafted polystyrene chains. This strategy led the ligand away from the core bead, depending on the length of the polystyrene block (number-average molecular weight determined by size exclusion chromatography = 1100–2250 g/mol). These supported complexes mediated a controlled polymerization of MMA, yielding polymers with controlled molar masses and low polydispersity indices. Moreover, after the polymerization, 96% of the initial copper was kept in the beads.