Molecular structure determination of Ni(II) diimine complex and DMA analysis of Ni(II) diimine-based polyethenes

Dynamic mechanical thermoanalysis showed that polyethene, prepared under su itable polymerization conditions with the Brookhart-type catalyst dibromo-N ,N'-1,2-acenaphthylenediylidenebis [2,6-bis(1-methylethyl)benzeneamine]Ni(I I)/methylaluminoxane (MAO), behaved Like an elastomer, even though no comon omer was added. A structural characterization showed that the polymers cont ained methyl to hexyl branches and some longer branches. The effect of the polymerization conditions on branching was investigated through variations in the pressure and temperature of the polymerization. Depending on the deg ree and type of branching, polyethene was either quite amorphous or highly crystalline with a high melting temperature. The solid-state structure of t he catalyst dibromo-N,N'-1,2-acenaphthylenediylidenebis [2,6-bis(1-methylet hyl)benzeneamine]Ni(II) consisted of two centrosymmetrically related monome ric moieties, where Ni atoms mere bridged by two bromide ligands. The Ni at om was five-coordinated, with a square pyramidal coordination polyhedron. T he sixth coordination site of the octahedral geometry was effectively block ed by the isopropyl groups of the 2,6-C6H3(i-Pr) substituents of the diimin e ligand. In solution in the presence of MAO, the longer bridging Ni-Br bon ds broke, and the complex dissociated to a monomeric species. (C) 2001 John Wiley & Sons, Inc. 2001