Highly Regioselective Transition-Metal-Catalyzed 1-Alkene Polymerizations: A Simple Method for the Detection and Precise Determination of Regioirregular Monomer Enchainments

The potentialities of this approach are illustrated for propene polymn. promoted by two well-known ansa-metallocene catalysts (cocatalyst: methylaluminoxane, MAO): the isotactic-specific rac-Me2Si(1-indenyl)2ZrCl2 (I), and the syndiotactic-specific (Me)(Ph)C(cyclopentadienyl)(9-fluorenyl)ZrCl2 (II). A series of copolymn. expts. at variable ethene-1-13C-propene feeding ratios in the presence of I/MAO or II/MAO was carried out to locate the value of ethene incorporation above which "all" 2,1-propene units are followed by an ethene one. The higher regioselectivity and regioirregular sequences of the copolymers were clearly detected by 13C NMR. The 13C NMR spectra of an isotactic polypropylene prepd. with I/MAO at 10°, a copolymer of propene contg. 2.9 mol% of ethene-1-13C prepd. with I/MAO, and an ethene-1-13C-propene copolymer (ethene content 2.5 mol%) prepd. with II/MAO, were presented