Allyl ansa‐Lanthanidocenes: Single‐Component, Single‐Site Catalysts for Controlled Syndiospecific Styrene and Styrene–Ethylene (Co)Polymerization

Abstract

A series of new neutral allyl Group 3 metal complexes bearing ansa-bridged fluorenyl/cyclopentadienyl ligands [[Flu-EMe(2)-(3-R-Cp)]Ln(eta(3)-C(3)H(5))(THF)] (E=C, R=H, Ln=Y (2), La (3), Nd (4), Sm (5); R=tBu, Ln=Y (8), Nd (9); E=Si, R=H, Ln=Y (12), Nd (13)) were synthesized in good yields via salt metathesis protocols. The complexes were characterized by elemental analysis, NMR spectroscopy for diamagnetic complexes, and single-crystal X-ray diffraction studies for 2, 4, 9 and 12. Some of the allyl ansa-lanthanidocenes, especially 4, are effective single-component catalysts for the polymerization of styrene, giving pure syndiotactic polystyrenes (rrrr > 99 %) with low to high molecular weights (M(n)=6000-135,000 g mol(-1)) and narrow polydispersities (M(w)/M(n)=1.2-2.6). The catalyst systems are remarkably stable, capable of polymerizing styrene up to 120 degrees C with high activities, while maintaining high syndiotacticity via chain-end control as established by a Bernoullian analysis. Highly effective copolymerization of styrene with ethylene was achieved using neodymium complex 4 (activity up to 2530 kg PS-PE mol(-1) h(-1)) to give true copolymers void of homopolymers with M(n)=9000-152,000 g mol(-1) and narrow polydispersities (M(w)/M(n)=1.2-2.5). The nature of the resultant P(S-co-E) copolymers was ascertained by NMR, size-exclusion chromatography/refractive index/UV, temperature rising elusion fractionation, and differential scanning calorimetry. It is shown that, regardless the amount of ethylene incorporated (1-50 mol %), P(S-co-E) copolymers have a microstructure predominantly made of long highly syndiotactic PS sequences separated by single or few ethylene units. Co-monomers feed and polymerization temperature can be used straightforwardly to manipulate with the physical and mechanical characteristics of the P(S-co-E) copolymers (molecular weights and distributions, co-monomer content, microstructure, T(m), T(g), T(c)).

Recent Advances in Rare Earth Complexes Bearing Allyl Ligands and Their Reactivity towards Conjugated Dienes and Styrene Polymerization

“…As for the ansa derivative 11 Nd , it was synthesized by ionic metathesis between K[1,3-(SiMe3)2C3H3] and [{Me 2 C(Cp)(Flu)}Nd(µ-Cl)] 2 and was found unsolvated. It was shown that 11 Nd acts as a single-component catalyst for the polymerization of styrene, and produces sPS albeit at a much lower rate (TOF = 20-60 h −1 ) than the regular allyl compounds {Me 2 C(Cp)(Flu)}RE(η 3 -C 3 H 5 )(THF) (RE = Y, La, Nd, 1000-17,000 h −1 ) [40]. Using DFT (Density Functional Theory) studies, the origin of the syndiospecificity control, due to a chain-end control mechanism (CEM), was proposed to result from the conjunction of the minimization of two repulsion effects: the classical phenyl (incoming monomer)-phenyl (last unit inserted) one during the growing of the polymer chain, and also of the repulsion between the fluorenyl ligand and the incoming styrene unit [41].…”

Synthesis of ethylene–styrene copolymer containing syndiotactic polystyrene sequence by trivalent titanium catalyst

“…Hou and co-workers 18 have reported that rare-earth metal-based catalyst systems promote not only the syndiotactic homopolymerization of styrene, but also copolymerization with ethylene, in which the Cp¢Sc(CH 2 SiTMS) 2 /Ph 3 CÁB(C 6 F 5 ) 4 [Cp¢¼C 5 Me 4 (CH 2 TMS)] catalyst system produces a multi-block copolymer consisting of a crystalline SPS part and an ethylene-rich part. Carpentier and co-workers 19 have also reported an ansa-lanthanidocene catalyst that can synthesize a copolymer containing long syndiotactic styrene-styrene sequences separated by a single or a few ethylene units. Meanwhile, it has been previously reported that the copolymeric fraction separated from the mixture obtained by the CpTiCl 3 /MAO system contains a similar long syndiotactic styrene-styrene sequence.…”

Groups 3 and 4 single-site catalysts for styrene–ethylene and styrene–α-olefin copolymerization

“…The copolymers composition could be easily controlled by the monomer feeds over a wide range of composition, playing either with ethylene pressure and/or styrene concentration. The unusual higher affinity of those complexes towards styrene compared to ethylene was illustrated by the fact that no polymerization activity was detected at low styrene concentration (<1.2 mol/L) [95].…”

“…The effect of bulky substituents on the Cp moiety as well as the influence of the bridge atom were also investigated and revealed that this system is very sensitive to an increase in the steric bulkiness and that a non-hindered environment is crucial to achieve good catalytic performances [95].…”

“…This system yields poly(styrene-co-ethylene) composed of long syndiotactic polystyrene sequences connected by isolated ethylene units [95].…”