Copolymerization of styrene with CO catalysed by palladium-substituted 1,10-phenanthroline bis(methoxycarbonyl) complexes [Pd(L-L)(COOMe)(2)]

A new class of highly effective homogeneous palladium bis(methoxycarbonyl) complexes Pd(L-L)(COOMe)(2), where (L-L) are substituted phenanthroline lig ands, has been developed for the production of syndiotactic alternating sty rene-carbon monoxide copolymers. The essential feature of this novel cataly tic system is that it is formed by palladium complex, Pd(L-L)(COOMe)(2), an acid cocatalyst, (L-L)HPF6, bearing a weakly coordinating counter anion, a nd an oxidant, such as 1,4-naphthoquinone (1,4-NQ). The palladium/acid coca talyst molar ratio has been explored. A maximum of copolymerization activit y was obtained at 1/1 molar ratio. For a series of palladium catalysts, Pd( phen)(COOMe)(2) appeared to be the most active one. The effect of substitue nts at the ligand in Pd(L-L)(COOMe)(2) on the copolymerization activity was studied. The tacticity of alternating copolymers obtained with different P d(L-L)(COOMe)(2) catalysts was determined by NMR spectroscopy. The copolyme rs were thermally characterised by TGA and DSC.