RESUMO
Tandem catalysis in a single medium presents challenges and opportunities for creating novel synthetic protocols. Thus far, only two homogeneous catalysts have been used in tandem. Herein, we report that it is possible to coordinate the action of three well-defined homogeneous catalysts to produce a wide range of branched polyethylenes from a single monomer. Thus, ([(eta(5)-C(5)Me(4))SiMe(2)(eta(1)-NCMe(3))]TiMe)(MeB(C(6)F(5))(3)) (1), [(C(6)H(5))(2)PC(6)H(4)C(OB(C(6)F(5))(3))O-kappa(2)P,O]Ni(eta(3)-CH(2)C(6)H(5)) (2), and ((H(3)C)C[N(C(6)H(5))]C[O-B(C(6)F(5))(3)][N(C(6)H(5))]-kappa(2)N,N)Ni(eta(3)-CH(2)C(6)H(5)) (3) react with ethylene to produce branched polyethylene with structures that cannot be obtained using a single- or a two-component catalyst combination. The properties of the polyethylene depend on the ratio of the three catalysts. High-throughput screening techniques proved essential for optimizing reaction conditions and for probing how the catalyst composition influences the polymer properties.
RESUMO
A small variation in the substituent R' on the metallocene catalyst employed in the copolymerization of ethene and propene leads to a highly alternating (81-83%) structure (1) rather than a statistical copolymer. Such copolymers were until recently only accessible by hydrogenation of polyisoprene or 1,4-poly(pentadiene).
