Polymerization of Methyl Methacrylate with Chloro Zirconocene Enolates

Abstract

Summary: The polymerization of methyl methacrylate (MMA) in the presence of the neutral chloro zirconocene enolates, Cp2ZrCl[OC(OMe)CMe2] (1), Me4C2(Cp)2ZrCl[OC(OMe)CMe2] (2), and Me2C(Cp)2ZrCl[OC(OMe)CMe2] (3), was investigated. None of these compounds is catalytically active on its own. They could be activated by adding Ph3CB(C6F5)4 (4); however, only if the initial concentration of enolate is higher than that of the perfluorated phenyl borate. Polymers were produced with a number average molar mass of up to 100 000 g/mol and a dispersion index of 1.1–1.3 with mixtures comprising 1 and 4 or 2 and 4. The degree of polymerization depends only on the quantity of excess enolate and not on the absolute concentration of the initiator components. In contrast, a mixture of 3 and 4 was not very active. Kinetic modeling of the systems as well as NMR spectroscopic investigations indicate that a bimetallic mechanism can describe chain growth. The activity of these catalytic systems depends on the structure of the ligand. The two zirconocenes with bridged cyclopentadienyl ligands, (2) and (3), convert MMA considerably slower. In addition to the methyl zirconocene enolates with unbridged cyclopentadienyl ligands, the corresponding chloro zirconocene enolates are also suitable for the polymerization of MMA. The latter compounds offer the advantage that preparations for the production of the initiators are comparatively simple.Structures of investigated initiators.magnified imageStructures of investigated initiators.

Coordination Polymerization of Polar Vinyl Monomers by Single-Site Metal Catalysts

“…This mechanistic insight brought about an efficient and living polymerization system at or below 0 °C by simply substituting the slow initiating Cp 2 ZrMe 2 with the preformed neutral zirconocene enolate Cp 2 ZrMe[OC(O t Bu)CMe 2 ]: namely the [Cp 2 ZrMe(THF)] + [BPh 4 ] − /Cp 2 ZrMe[OC(O t Bu)CMe 2 ] pair . Further studies by the groups of Collins and Bandermann showed that neutral ester enolate Cp 2 ZrMe[OC(OR)CMe 2 ] (R = Me, t Bu) is inactive by itself, but its combination with the metallocenium cation Cp 2 ZrMe + as catalyst is highly active and of living characteristics in a bimolecular MMA polymerization process. , Other analogous catalyst/initiator pairs, such as the [Cp 2 ZrCl] + [B(C 6 F 5 ) 4 ] − /Cp 2 ZrCl[OC(OMe)CMe 2 ] pair derived from the proposed complex reaction sequence starting with Cp 2 ZrCl[OC(OMe)CMe 2 ] and [Ph 3 C][B(C 6 F 5 ) 4 ], have also been reported …”

“…161,164 Other analogous catalyst/initiator , have also been reported. 165 The initiator/catalyst components have been covalently linked via a robust µ-oxo linkage into a dinuclear enolate zirconocene complex (Scheme 8). 166 The corresponding cationic enolate complex, which consists of both the ester enolate initiator and the cationic zirconocene catalyst sites, can be generated upon treatment with [PhNMe 2 H][B(C 6 F 5 ) 4 ], affording a highly active, controlled polymerization system producing st-PMMA (g80% rr) with high I* (g78%) and TOF (>380 h -1 ) at T p e -20 °C.…”

Coordination−Addition Polymerization and Kinetic Resolution of Methacrylamides by Chiral Metallocene Catalysts

“…There is increasing interest in the utilization of technologically important, single-site cationic group 4 metallocene catalysts, which have been extensively investigated and successfully employed for the (co)polymerization of nonpolar vinyl monomers (α-olefins in particular), for polymerizations of polar, functionalized vinyl monomers including methacrylates, − acrylates, ,− acrylamides, − and methyl vinyl ketone . The polymerization of (meth)acrylates has also been studied computationally. − Certain catalyst structures exhibit a high degree of control over polymerization characteristics (activity and efficiency; polymer molecular weight, MW; MW distribution, MWD; livingness) and stereochemistry (polymer tacticity and stereocontrol mechanism), enabling the ambient-temperature synthesis of highly isotactic poly(methacrylate)s (≥95% mm ) ,,,, and poly(acrylamide)s (>99% mm ) − using chiral C 2 -ligated zirconocenium complexes as well as highly syndiotactic poly(methacrylate)s (≥94% rr ) using chiral C s -ligated zirconocenium complexes.…”

Syndioselective MMA Polymerization by Group 4 Constrained Geometry Catalysts: A Combined Experimental and Theoretical Study

“…In comparison, the polymerization of polar vinyl monomers with such highly electron-deficient group 4 metallocene and related complexes has been investigated to a much lesser extent . Nonetheless, there is increasing interest in the latter area, with several types of group 4 metallocene complexes being examined for polymerizations of methacrylates, − acrylates, ,− acrylamides, − and methyl vinyl ketone . The polymerization of (meth)acrylates has also been studied computationally. − Overall, these studies have been focused on the following four major aspects of polymerization: activity/efficiency (catalyst turnover frequency and initiator efficiency), stereospecificity (polymer tacticity and stereocontrol mechanism), control (polymer molecular weight, MW, and molecular weight distribution, MWD, as well as livingness and block copolymer production), and mechanism (kinetics and elementary reactions).…”