1075682-66-4Relevant articles and documents
Neutral metallocene ester enolate and non-metallocene alkoxy complexes of zirconium for catalytic ring-opening polymerization of cyclic esters
Ning, Yalan,Zhang, Yuetao,Rodriguez-Delgado, Antonio,Chen, Eugene Y.-X.
, p. 5632 - 5640 (2008)
Four neutral zirconocene bis(ester enolate) and non-zirconocene bis(alkoxy) complexes have been employed for ring-opening polymerizations and chain transfer polymerizations of L-lactide (L-LA) and e-caprolactone (ε-CL). All C2v-, C2-, and Cs-ligated neutral zirconocene bis(ester enolate) complexes effectively polymerize ε-CL at 80°C with high (>90%) initiator efficiencies. The Cs-ligated complex Ph 2C(Cp)(Flu)Zr[OC(OiPr)=CMe2]2 (1) also promotes highly efficient polymerization of L-LA and is at least 100 times more reactive than the C2v.,- and C2-ligated analogues. The L-LA polymerization by 1 exhibits living characteristics, producing PLA with quantitative isotacticity (no sign of monomer epimerization) and controlled molecular weight. This polymerization follows firstorder kinetics with respect to both [L-LA] and [1], consistent with a monometallic, coordinationanionic propagation mechanism. The structurally characterized non-zirconocene bis(alkoxy) complex [(2,6-iPr2C6H 4)N(CH2)3N(2,6-iPr2C 6H4)]Zr(OiPr)2[O=C(NMe 2)CHMe2] (2) has been synthesized in quantitative yield from the reaction of the zirconium bis(amido) precursor with isopropyl isobutyrate. Complex 2 behaves as a single-site catalyst for polymerizations of both ε-CL and L-LA, unlike the comparative homoleptic zirconium tetraisopropoxy complex, which shows multisite behavior for the same processes. Both the zirconocene 1 and the non-zirconocene 2 catalyze efficient chain transfer polymerization in the presence of iPrOH as a chain transfer reagent (CTR) for the catalytic production of PLA and PCL, respectively; however, the metallocene system is more robust (in terms of ligand stability and maintaining the polymerization rate) toward an excess of a protic CTR than the present non-metallocene system.
