Steric and electronic effects of R in (2-(4-R-C 6H 4)indenyl) 2ZrCl 2 catalysts on the synthesis of elastomeric polypropylene

Abstract

Metallocene catalysts derived from bis(2-arylindenyl)zirconium dichloride catalysts yield elastomeric stereoblock polypropylene. A study of the steric and electronic effects of varying the 4-substituent of bis(2-(4-R-C 6H 4)indenyl)zirconium dichloride [( 1 RH, 2 RMe, 3 REt, 4 R nBu, 5 R tBu, 6 RSiMe 3, 7 RCF 3, 8 RCl)] on propylene polymerization at 25, 50, 75 psig and bulk propylene revealed that the polymerization behavior of these catalysts is not strongly influenced by the nature of the substituent in the 4-position of the 2-aryl substituent. Examinations of the microstructure of the elastomeric polypropylenes produced showed that for catalysts 2– 8 the isotacticities varied over a small range and were similar to those produced by catalyst 1 (20%≤[mmmm]≤44%). The catalyst productivities and molecular weights also showed the same trend. Complex 3 was crystallographically characterized and was found to crystallize in exclusively the meso conformation.