Quantitative 13C NMR Analysis of Isotactic Ethylene–Propylene Copolymers Prepared with Metallocene Catalyst: Effect of Ethylene on Polymerization Mechanisms

Low molecular weight homopolypropylene and ethylene–propylene copolymers with low ethylene content have been produced with a highly stereoselective metallocene catalyst in the presence of dihydrogen. Quantitative 13C NMR analysis allowed the detection of regioirregular (2,1-insertions) propylene units both in propylene homosequences and in ethylene–propylene sequences, and of different types of end groups. The microstructure of the polymers has been correlated with polymerization mechanisms, and the effect of ethylene on polymer regioregularity, termination and initiation steps has been investigated. The amount of 2,1-misinserted propylene units followed by one ethylene unit increases with increasing ethylene content in the polymer, which confirms that ethylene insertion after a 2,1-misinsertion is favored over propylene 1,2-insertion. Additionally, addition of ethylene reduces the frequency of secondary insertions. Under the investigated polymerization conditions, the dominating termination route was cha...