Design your own elastomeric or stereoregular polymer

This study reports the synthesis and activity as precatalysts for the polymerization of propylene of five racemic group 4 complexes, cis‐[p‐R′C 6 H 4 C(NR) 2 ] 2 MX 2 (R′ = CH 3 , R = SiMe 3 , M = Ti, X = Cl ( 1 ); R′ = CH 3 , R = SiMe 3 , M = Zr, X = Cl ( 2 ); R′ = H, R = i‐pr, M = Zr, X = Cl ( 3 ); R′ = CH 3 , R = SiMe 3 , M = Zr, X = CH 3 ( 4 )) and (acac) 2 MCl 2 (M = Ti ( 5 ), M = Zr ( 6 )) (acac = acetylacetone). The hydrocarbyl complex 4 was prepared by the alkylation of the corresponding complex 2 with MeLi·LiBr. Reaction of complex 4 with B(C 6 F 5 ) 3 or all complexes with MAO (MAO = methylalumoxane) results in the formation of a “cationic” intermediate complex which rapidly reacts with the incoming monomer. Some of the complexes catalyze the stereoregular polymerization of propylene only under pressure in either toluene or CH 2 Cl 2 , producing polypropylene with very large isotacticities (mmmm % = ∼95–98), high melting points (140–154 °C) and similar molecular weights as compared with cyclopentadienyl complexes, whereas complex 5 is active for the polymerization of elastomeric polypropylene. Copyright © 2003 John Wiley & Sons, Ltd.