Homo- and copolymerization of strained cyclic olefins with new palladium(II) complexes bearing ethylene-bridged heterodonor ligands

Amorphous and high molar mass polymers of norbornene and phenylnorbornene (endo/exo ratio of 80/20) were prepared by the use of new dicationic palladium(II) single-component catalyst of the general type [Pd(L∩L)(NCCH₃)₂](BF₄) _2· [(L∩L) = 2-(diphenylarsino)-1-(methylthio)ethane (S∩As, 1) (4), 2-(diphenylphosphino)-1-methylthio)ethane (S∩P, 2) (5), 1, 2-bis(diphenylphosphino)ethane (P∩P, 3) (6). With increasing the trans influence of the donor atom in the ligands (P>As>S) the polymerization activity of the catalysts towards polymerization of norbornene increases instantly. Both the molecular weight and the thermal behavior of the polymer can be tailored using ethene as chain transfer agent. Catalyst 4 is also active towards the alternating copolymerization of carbon monoxide and norbornene. The isolated copolymer is highly soluble in toluene, THF and chlorinated solvents. The DSC measurement of the norbornene-carbon monoxide copolymer showed a melting temperature (T_m) of 241 °C (ΔH_f = 47.3 J/g) and a glass transition temperature (T_g) of 161 °C which is about 170°C lower compared to the homopolynorbornene (T_g ≅ 330°C).