SYNDIOTACTIC-SPECIFIC POLYMERIZATION OF PROPENE WITH NICKEL-BASED CATALYSTS .2. REGIOCHEMISTRY AND STEREOCHEMISTRY OF THE INITIATION STEPS

A homogeneous catalytic system based on a suitable Ni(II) diimine deri vative and methylaluminoxane affords predominantly syndiotactic polypr opylene at subambient temperatures. The polymer microstructure is that expected for a ''chain-end'' mechanism of steric control. NMR analysi s of polymer samples carrying selectively C-13-enriched end groups ind icates a largely prevailing 1,2 regiochemistry for the insertion of pr opene into Ni-(CH3)-C-13 bonds in the initiation step and a syndiotact ic steric control already effective in the second propagation step.