Living/controlled anionic polymerization and copolymerization of epichlorohydrin with tetraoctylammonium bromide-Triisobutylaluminum initiating systems

A weakly nucleophilic initiating system obtained by the combination of triisobutylaluminum and tetraoctylammonium bromide has been successfully used to achieve the controlled polymerization of epichlorohydrin (ECH) in hydrocarbon at temperatures ranging from -30 degrees C to room temperature. Besides the formation of a 1:1 aluminate complex of low nucleophilicity between the aluminum derivative and the tetraalkylammonium salt, the strategy consists of the formation of a strongly activating complex between the Lewis acid and the epoxide monomer. To that aim trialkylaluminum is added in slight excess with respect to the tetraalkylammonium salt ([i-BU3Al]/[NOct(4)Br] > 1). In these conditions the reactivity of ECH toward nucleophiles is strongly enhanced and the ring opening polymerization proceeds in the presence of weak nucleophiles leading to nonreacted chloromethyl function of the epichlorohydrin. This contrasts with conventional anionic polymerization, which requires much stronger nucleophiles for the ring opening. Fast and controlled polymerization of ECH up to high molar masses and the synthesis of random and block copolymers with propylene oxide were readily achieved

Blue Phosphorescent Zwitterionic Iridium(III) Complexes Featuring Weakly Coordinating <i>nido</i>-Carborane-Based Ligands

We report the development of a new class of phosphorescent zwitterionic <i>bis</i>(heteroleptic) Ir­(III) compounds containing pyridyl ligands with weakly coordinating <i>nido</i>-carboranyl substituents. Treatment of phenylpyridine-based Ir­(III) precursors with <i>C</i>-substituted <i>ortho</i>-carboranyl­pyridines in 2-ethoxyethanol results in a facile carborane deboronation and the formation of robust and highly luminescent metal complexes. The resulting <i>nido</i>-carboranyl fragments associate with the cationic Ir­(III) center through primarily electrostatic interactions. These compounds phosphoresce at blue wavelengths (450–470 nm) both in a poly­(methyl methacrylate) (PMMA) matrix and in solution at 77 K. These complexes display structural stability at temperatures beyond 300 °C and quantum yields greater than 40%. Importantly, the observed quantum yields correspond to a dramatic 10-fold enhancement over the previously reported Ir­(III) congeners featuring carboranyl-containing ligands in which the boron cluster is covalently attached to the metal. Ultimately, this work suggests that the use of a ligand framework containing a weakly coordinating anionic component can provide a new avenue for designing efficient Ir­(III)-based phosphorescent emitters

Synthesis of Linear High Molar Mass Glycidol-Based Polymers by Monomer-Activated Anionic Polymerization

Linear polyglycidols of high molar masses were prepared by the monomer-activated anionic polymerization of the corresponding protected monomers, ethoxyethyl glycidyl ether and tert-butyl glycidyl ether, using a system composed of tetraoctylammonium bromide as initiator and triisobutylaluminum as monomer activator. The aluminic compound was used in 1.5-5-fold excess compared to the initiator. Linear poly(ethoxyethyl glycidyl ether) and poly(tert-butyl glycidyl ether), with narrow chain dispersity and controlled high molar masses, up to 85000 g/mol, were prepared at 0 degrees C in a few hours. Deprotection of hydroxyl functions by acidic treatment of file polymers was shown to proceed quantitatively and cleanly affording the corresponding linear polyglycerol and validating the use of these protecting groups. The copolymerization of protected glycidols with propylene oxide and butene oxide was also investigated with the goal to broaden the scope of this synthetic approach to various polyethers and copolyethers