Based on the successful isolation of polynuclear Nd-Al bimetallic complex which alone can initiate diene polymerization without the presence of the co-catalyst trialkyl aluminium

the effects of active speecies

additional trialkyl aluminium

and monomer concentrations as well as temperature on butadiene polymerization were studied in detail. The results indicate that there is a relationship between the molecular weight and the microstructure of obtained polybutadiene

that is

the lower the molecular weight and the microstructure of obtained polybutadiene

that is

the lower the molecular weight

the lower the cis-1

4 content and the higher the trans-1

4 content. To explain the experimental results

a new view which involves the reaction of the propagating polymer chain on polymerization process was put forward and some explanation according to syn-anti isomerization of π-allyl mechanism was given.