Polymerization of 1,3-butadiene with VO(P204)2 and VO(P507)2 activated by alkylaluminum

The oxovanadium phosphonates (VO(P204)2 and VO(P507)2) activated by various alkylaluminums (AlR3, R = Et, i-Bu, n-Oct; HAlR2, R = Et, i-Bu) were examined in butadiene (Bd) polymerization. Both VO(P204)2 and VO(P507)2 showed higher activity than those of classical vanadium-based catalysts (e.g. VOCl3, V(acac)3). Among the examined catalysts, the VO(P204)2/Al(Oct)3 system (I) revealed the highest catalytic activity, giving the poly(Bd) bearing Mn of 3.76 × 104 g/mol, and Mw/Mn ratio of 2.9, when the [Al]/[V] molar ratio was 4.0 at 40 °C. The polymerization rate for I is of the first order with respect to the concentration of monomer. High thermal stability of I was found, since a fairly good catalytic activity was achieved even at 70 °C (polymer yield > 33%); the Mn value and Mw/Mn ratio were independent of polymerization temperature in the range of 40-70 °C. By IR and DSC, the poly(Bd)s obtained had high 1,2-unit content (>65%) with atactic configuration. The 1,2-unit content of the polymers obtained by I was nearly unchanged, regardless of variation of reaction conditions, i.e. [Al]/[V], ageing time, and reaction temperature, indicating the high stability of stereospecificity of the active sites.