Oligomeric And Polymeric Bibenzimidazole Based Metal Complexes And Crosslinked Polyethylenimine Based Flame Retardants
In Part I, a simple and mild condensation route for the synthesis of novel bibenzimidazole oligomers and polymers is described using methyl 2,2,2-trichloroacetimidate as a key starting material. The dimer, trimer, tetramer, and polymers of bibenzimidazole were synthesized as a new series of potential conjugated chelating ligands for the metallopolymer studies. The polymers show the maximum absorption at around 400 nm. The optical band gap of the polymer is estimated to be 2.68 eV.
In Part II, a series of multinuclear Ru complexes containing di-, tetra-, and octa-RuII centers based on the oligomeric bibenzimidazoles were synthesized and characterized. The species with high nuclearity exhibit extended, one-dimensional structures. They show very intense ligand-centered (LC) absorptions (ε up to 3.6 × 105
M–1·cm–1) and moderately intense metal-to-ligand charge transfer bands in the visible region (ε up to 6.6 × 104 M–1·cm–1). The interactions between the Ru metal centers across the bidentate bibenzimidazole ligands, and along the oligomeric bibenzimidazole ligands are relatively weak, which is not expected. In Part III, the homochiral multinuclear Ru complexes of the oligomeric bibenzimidazoles were synthesized stereospecifically using Λ-[Ru(bpy)2(py)2][(−)- O,O'-dibenzoyl-L-tartrate]⋅12H2O as the enantiomerically pure chiral building block. The complexation of bibenzimidazole and the chiral building block proceeds with the complete retention of configuration. The tetra-Ru complex has an estimate size of 2.1 × 1.1 × 1.0 nm3. They were characterized by means of circular dichroism, NMR spectroscopy, and mass spectrometry. In Part IV, a new intumescent flame retardant system for use in olefinic polymers was discovered by crosslinking polyethylenimine ("Lupasol") with pyromellitic dianhydride, and then further treating with phosphoric acid to make the phosphate salts. The LOI of the phosphate salts can be greater than 70.0, and the char yield at 800 °C reaches 37.6%, which indicates that they could be non-halogenated, enviromental friendly, low smoke level, and cost effective intumescent flame retardants for polyolefins.