Coordinative Chain Transfer Polymerization Research Articles

Polymerization via Insertion of Ethylene into Al-C bond under Mild Conditions: Mechanistic Studies on the Promotion Exerted by a Catalytic Amount of Cationic Gadolinium Metallocene.

The cationic gadolinium metallocene [(C5 Me5 )2 Gd][B(C6 F5 )4 ], when combined with an excess amount of Al(i Bu)3 , efficiently produces polyethylene at 80 °C under 0.8 MPa pressure of ethylene. After quenching, the resulting polyethylene has ethyl group at one end and isobutyl group at the other terminal. Because no Gd-alkyl species appears to be involved, a mechanism with conventional coordinative chain transfer polymerization (CCTP) is not feasible. Density functional theory (DFT) analyses indicate a novel mechanism in which the cationic Gd plays a crucial role by coordinating ethylene and assists the insertion of the coordinated ethylene into Al-C bond.

Mechanistic study on the metallocene-based tandem catalytic coordinative chain transfer polymerization for the synthesis of highly branched polyolefins

Creation and control of long-chain branches (LCBs) in coordination polymerization of olefins is an enduring focus of research in both academia and industry. We have recently introduced a tandem catalytic coordinative chain transfer polymerization reaction where upon the concerted function of the polymerization catalyst, the chain transfer agent (CTA), and the displacement catalyst, a highly branched microstructure can be formed. Here we introduce a new tandem catalytic system using Et(Ind)2ZrCl2 as the polymerization catalyst. Despite the optimal reaction temperature for the cooperative function of catalyst components is lower than the ideal temperature for the productivity of the metallocene catalyst, the formation of branches is evident from the decrease and broadening of melting peaks and deviation of rheological properties from characteristic behavior of linear chains in cole–cole plots. Surprisingly, the introduction of the displacement catalyst in CCTP of 1-hexene resulted in low yields and too short polymer chains. Accordingly, we elaborate on the mechanism of this reaction, specifically, we show how the optimal conditions for the (BiPy)2FeEt2 displacement catalyst depend on the monomer type. Namely, the presence of a β–agostic interaction in the bimetallic intermediate formed by the CTA and the displacement catalyst alters the structure of the latter when monomers longer than ethylene are present. This report suggests that our proposed method for the synthesis of branched polyolefins has a great potential for being used in the currently available industrial plants that employ classic metallocene catalysts.

Optical Purity as a Programmable Variable for Controlling Polyolefin Tacticity in Living Coordinative Chain Transfer Polymerization: Application to the Stereomodulated LCCTP of α,ω-Nonconjugated Dienes

Two-state, stereomodulated living coordinative chain transfer polymerization (LCCTP) of 1,6-heptadiene has been achieved to produce a series of cis-poly(methylene-1,3-cyclohexane) (cis-PMCH) with stereochemical microstructures that vary between two limiting forms as a function of the optical purity of the chiral C1-symmetric hafnium preinitiator 1 when activated by the borate co-initiator B1 in the presence of a fixed excess amount of ZnEt2. Optical purity as a programmable variable was demonstrated by premixing the pure homochiral (SC,SHf) and (RC,RHf) enantiomers of 1 in different ratios prior to activation. In contrast, the LCCTP of 1,5-hexadiene using a “racemic” mixture of 1 to produce cis/trans-poly(methylene-1,3-cyclopentane) (cis/trans-PMCP) was less successful due to the loss of stereocontrol for insertion under chain transfer conditions that arises with site epimerization at the transition metal center. A correlation is proposed between the diastereoselectivity and efficiency for the cyclization step in propagation and the magnitude of site epimerization due to reversible chain transfer. These results serve to validate the strategy of using the optical purity of an initiator as a programmable parameter for controlling polyolefin tacticity as well as to better establish the criteria that are required for achieving successful stereomodulated LCCTP for the production of next generation polyolefin materials.

Polyolefin chain shuttling at ansa-metallocene catalysts: legend and reality

Several papers have claimed the amenability for binary metallocene systems to undergo coordinative chain transfer polymerization (CCTP) to produce stereoblock isotactic/syndiotactic polypropylene materials. In this work, we explored through high throughput experimentation (HTE) tools and methods the propensity of the isotactic-selective rac-Me2Si(2-Me-4-Ph-1-Ind)2ZrCl2 (2) catalyst to mediate propene CCTP, individually or in tandem with the syndiotactic-selective ansa-zirconocene Ph2C(Cp)(2,7-di-tBu-9-Flu)ZrCl2 (3), using ZnEt2 and methylalumoxane (MAO) as chain shuttling agents. The results demonstrated that 2 is not prone to propene CCTP, and therefore does not yield stereoblock PP materials when used in racemic form or in tandem with other metallocenes. An unambiguous method to demonstrate the occurrence of CCTP in isotactic propene polymerization, based on the microstructural characterization of the sample by 13CNMR spectroscopy, is also proposed.

In-situ block copolymerization of 1,3-butadiene with cyclohexene oxide and trimethylene carbonate via combination of coordinative chain transfer polymerization and ring opening polymerization by neodymium-based catalyst system

Incorporating polar segment or polar block to non-polar polybutadiene is eye-catching as they can modify the interfacial energy and adhesion between polybutadiene matrix and polar materials. Herein, we report the in-situ preparation of well-defined polybutadiene-based block copolymers (poly(1,3-butadiene)-b-poly(cyclohexene oxide) and poly(1,3-butadiene)-b-poly(trimethylene carbonate)) using a commercially available neodymium-based catalytic system Nd(vers)3/AliBu2H/Me2SiCl2. First, the polybutadiene block was conveniently and highly efficiently synthesized via Coordinative Chain Transfer Polymerization (CCTP), yielding 5–11 polymer chains per catalyst molecule. This system revealed a high catalytic efficiency and well-controlled fashion, narrowly distributed together with well-regulated molecular weights were also resulted. Then, taking advantage of the living metal-capped polybutadienyl chain that were produced during the CCTP reaction in the first step, in-situ Ring Opening Polymerization of cyclohexene oxide, trimethylene carbonate were assessed. All the products were carefully characterized by combination of GPC, FTIR, 1H NMR, 2D DOSY NMR and DSC analysis, providing advantages and limitations for this method to prepare nonpolar-polar block copolymers.

Evidence of coordinative chain transfer polymerization of isoprene using iron iminopyridine/ZnEt2 catalytic systems

Herein, the first example of a reversible iron-mediated chain transfer polymerisation of isoprene with ZnEt2 as the chain transfer agent is reported.

Synthesis of Chain Shuttling Organometallic Compounds Capable of Producing Triblock Polyolefins

Organometallic oligomeric compounds with dual-headed structure R’-(M-R-)nM-R’ were developed enabling the synthesis of triblock polyolefins. The compounds comprise divalent linkers (R) derived from trivinylcyclohexane between two main group metals and norbornyl capping groups (R’). Due to the difference in steric hindrance, the chain transfer reaction in polymerization selectively involves the less hindered M–R bond, resulting in growth of polymer chains only from the R linker group with metals on both ends. The metal-terminated polymer can be further functionalized to form telechelic polymers or used in coordinative chain transfer polymerization to produce various triblock polyolefins. This paper presents the synthetic strategy and demonstrates the production of triblock polymers using the compounds in a scalable continuous solution polymerization process.

Crystal Structure of Decakis(μ-chloro)-tetrakis(1,2,4-triphenylcyclopentadienyl)-hexakis(tetrahydrofuran)-di-potassium-tetra-neodymium(III) Tetrahydrofuran Trisolvate

The crystal structure of decakis(μ-chloro)-tetrakis(1,2,4-triphenylcyclopentadienyl)-hexakis(tetrahydrofuran)-di-potassium-tetra-neodymium(III) tetrahydrofuran trisolvate, 1, is reported. The centrosymmetric complex 1 has a rare tetranuclear core [Ln4K2Cl10] and crystalizes in triclinic space group (P $$\bar{1}$$ ) with unit cell parameters: a = 11.9858(3) A, b = 14.0698(3) A, c = 19.8129(4) A, α = 74.1120(4)°, β = 81.2073(4)°, γ = 83.9521(4)° and Z = 1. The catalytic system based on 1 and nBuMg(O-2,6-tBu2-4-MeC6H2) exhibits moderate activity in coordinative chain transfer polymerization of ethylene. In case of the system 1/nBu2Mg, oligomerisation of ethylene was not detected. The mono(cyclopentadienyl) complex {[1,2-Ph2-4-(2-MeOC6H4)C5H2]NdCl5K(THF)2}2(THF)3 has been obtained from NdCl3(THF)2.5 and K[1,2-Ph2-4-(2-MeOC6H4)C5H2] (1:1) in THF, crystallized from a THF/hexane mixture, and structurally characterized.

Quantitative Validation of the Living Coordinative Chain-Transfer Polymerization of 1-Hexene Using Chromophore Quench Labeling

In this report, we apply the chromophore quench-labeling (CQL) technique to living, homogeneous polymerization catalysts and living coordinative chain-transfer polymerization (LCCTP) conditions. We...

Control over Branching Topology by Introducing a Dual Catalytic System in Coordinative Chain Transfer Polymerization of Olefins

Coordinative polymerization brings opportunities for producing well-defined long-chain branched polyolefins specifically by using homogeneous single-site catalysts. Herein, we report a new dual cat...

Polystyrene Chain Growth Initiated from Dialkylzinc for Synthesis of Polyolefin-Polystyrene BlockCopolymers.

Polyolefins (POs) are the most abundant polymers. However, synthesis of PO-based block copolymers has only rarely been achieved. We aimed to synthesize various PO-based block copolymers by coordinative chain transfer polymerization (CCTP) followed by anionic polymerization in one-pot via conversion of the CCTP product (polyolefinyl)2Zn to polyolefinyl-Li. The addition of 2 equiv t-BuLi to (1-octyl)2Zn (a model compound of (polyolefinyl)2Zn) and selective removal or decomposition of (tBu)2Zn by evacuation or heating at 130 °C afforded 1-octyl-Li. Attempts to convert (polyolefinyl)2Zn to polyolefinyl-Li were unsuccessful. However, polystyrene (PS) chains were efficiently grown from (polyolefinyl)2Zn; the addition of styrene monomers after treatment with t-BuLi and pentamethyldiethylenetriamine (PMDTA) in the presence of residual olefin monomers afforded PO-block-PSs. Organolithium species that might be generated in the pot of t-BuLi, PMDTA, and olefin monomers, i.e., [Me2NCH2CH2N(Me)CH2CH2N(Me)CH2Li, Me2NCH2CH2N(Me)Li·(PMDTA), pentylallyl-Li⋅(PMDTA)], as well as PhLi⋅(PMDTA), were screened as initiators to grow PS chains from (1-hexyl)2Zn, as well as from (polyolefinyl)2Zn. Pentylallyl-Li⋅(PMDTA) was the best initiator. The Mn values increased substantially after the styrene polymerization with some generation of homo-PSs (27–29%). The Mn values of the extracted homo-PS suggested that PS chains were grown mainly from polyolefinyl groups in [(polyolefinyl)2(pentylallyl)Zn]−[Li⋅(PMDTA)]+ formed by pentylallyl-Li⋅(PMDTA) acting onto (polyolefinyl)2Zn.

Coordinative chain transfer polymerization of 1-decene in the presence of a Ti-based diamine bis(phenolate) catalyst: a sustainable approach to produce low viscosity PAOs

A Ti-based diamine bis(phenolate) catalyst, [Ti{2,2′-(OC6H2-4,6-tBu2)2NHMePhMeNH}Cl2], was synthesized and fully characterized by elemental analysis and NMR spectroscopy.

Synthesis of Long-Chain Branched Polyolefins by Coordinative Chain Transfer Polymerization

Synthesis of long-chain branched polymers has been a crucial concern in the polyolefin industry. In this study, a method to produce long-chain branches (LCBs) in coordinative chain transfer copolymerization (CCTcoP) is suggested. A dialkylzinc compound bearing vinyl groups ((9-decenyl)2Zn) is prepared, which works well not only as a chain transfer agent but also as a comonomer in CCTcoP, resulting in the generation of LCBs. The generation of LCBs is confirmed by gel permeation chromatography studies and through the analysis of rheology data. The formation of LCBs by connecting the two growing polyolefin chains can facilitate the generation of polymers with molecular weights higher than that expected. Owing to the presence of LCBs, considerable shear thinning behavior is observed. Ethylene/1-octene copolymers can be prepared facilely to show almost the same shear thinning behavior with the commercial grade of low-density polyethylene, which is known to have a substantial amount of LCBs.

Coordinative Chain Transfer Polymerization of Butadiene with Functionalized Aluminum Reagents.

Functionalized aluminum alkyls enable effective coordinative chain transfer polymerization with selective chain initiation by the functionalized alkyl. (ω‐Aminoalkyl)diisobutylaluminum reagents (12 examples studied) obtained by hydroalumination of α‐amino‐ω‐enes with diisobutylaluminum hydride promote the stereoselective catalytic chain growth of butadiene on aluminum in the presence of Nd(versatate)3, Cp*2Nd(allyl), or Cp*2Gd(allyl) precatalysts and [PhNMe2H+]/[B(C6F5)4 −]. Carbazolyl‐ and indolylaluminum reagents result in efficient molecular weight control and chain initiation by the aminoalkyl rather than the isobutyl substituent bound to aluminum. As confirmed for (3‐(9H‐carbazol‐9‐yl)propyl)‐initiated polybutadiene (PBD), for example, by deuterium quenching studies, polymer chain transfer by β‐hydride transfer is negligible in comparison to back‐transfer to aluminum.

Coordinative Chain Transfer Polymerization of Butadiene with Functionalized Aluminum Reagents

AbstractFunctionalized aluminum alkyls enable effective coordinative chain transfer polymerization with selective chain initiation by the functionalized alkyl. (ω‐Aminoalkyl)diisobutylaluminum reagents (12 examples studied) obtained by hydroalumination of α‐amino‐ω‐enes with diisobutylaluminum hydride promote the stereoselective catalytic chain growth of butadiene on aluminum in the presence of Nd(versatate)3, Cp*2Nd(allyl), or Cp*2Gd(allyl) precatalysts and [PhNMe2H+]/[B(C6F5)4−]. Carbazolyl‐ and indolylaluminum reagents result in efficient molecular weight control and chain initiation by the aminoalkyl rather than the isobutyl substituent bound to aluminum. As confirmed for (3‐(9H‐carbazol‐9‐yl)propyl)‐initiated polybutadiene (PBD), for example, by deuterium quenching studies, polymer chain transfer by β‐hydride transfer is negligible in comparison to back‐transfer to aluminum.

Preparation of Half- and Post-Metallocene Hafnium Complexes with Tetrahydroquinoline and Tetrahydrophenanthroline Frameworks for Olefin Polymerization.

Hafnium complexes have drawn attention for their application as post-metallocene catalysts with unique performance in olefin polymerization. In this work, a series of half-metallocene HfMe2 complexes, bearing a tetrahydroquinoline framework, as well as a series of [Namido,N,Caryl]HfMe2-type post-metallocene complexes, bearing a tetrahydrophenanthroline framework, were prepared; the structures of the prepared Hf complexes were unambiguously confirmed by X-ray crystallography. When the prepared complexes were reacted with anhydrous [(C18H37)2N(H)Me]+[B(C6F5)4]−, desired ion-pair complexes, in which (C18H37)2NMe coordinated to the Hf center, were cleanly afforded. The activated complexes generated from the half-metallocene complexes were inactive for the copolymerization of ethylene/propylene, while those generated from post-metallocene complexes were active. Complex bearing bulky isopropyl substituents (12) exhibited the highest activity. However, the activity was approximately half that of the prototype pyridylamido-Hf Dow catalyst. The comonomer incorporation capability was also inferior to that of the pyridylamido-Hf Dow catalyst. However, 12 performed well in the coordinative chain transfer polymerization performed in the presence of (octyl)2Zn, converting all the fed (octyl)2Zn to (polyolefinyl)2Zn with controlled lengths of the polyolefinyl chain.

Lanthanide complexes mediated coordinative chain transfer polymerization of conjugated dienes

Tremendous advances has been witnessed in the past few years in the lanthanide complexes mediated coordinative chain transfer polymerization (CCTP) of conjugated dienes. CCTP features catalyst economy, well-controlling over both microstructure and architecture of the resulting polymers, and accessibility for novel (co)polymers. This review highlights the recent progresses made in the field of CCTP of dienes. After a brief introduction, the body of this review is divided into three parts: (1) principle of CCTP; (2) coordinative chain transfer homopolymerization of dienes; (3) coordinative chain transfer copolymerization of dienes. At the end, we present some challenges remaining in this area and our personal opinion regarding where this field should continue to develop. CCTP represents a novel strategy to prepare polydiene synthetic rubbers with controlled high molecular weight and narrow molecular weight distribution, which has reached the practical industrial application level, demonstrating a great potential in industrialization.

Synthesis of Linear α-Olefin Distributions with Flexible Mean Molecular Weight by a Ti-Al-Ni Catalyst System

The catalytic synthesis of linear α-olefins from ethylene is a key reaction in the chemical industry and one of the most important applications of homogeneous catalysis. Thus, novel protocols or concepts for the synthesis of linear α-olefins are highly desirable. Herein, we describe a trimetallic catalyst system (Ti-Al-Ni) consisting completely of earth-abundant metals. The titanium catalyst mediates coordinative chain transfer polymerization to the chain transfer agent triethylaluminum with multiple ethylene insertions prior to chain transfer. This Ti catalyst is combined with a simultaneously operating nickel catalyst. The nickel catalyst also undergoes chain transfer, displaces the grown alkyl chains via β-hydride elimination/transfer forming linear α-olefins, and recycles the chain transfer agent. The catalyst combination permits the highly efficient synthesis of various linear α-olefin distributions with flexible mean molecular weight with one catalyst system. Activities of more than 10000 kgeth mol–...

Peroxide-Mediated Alkyl–Alkyl Coupling of Dialkylzinc: A Useful Tool for Synthesis of ABA-Type Olefin Triblock Copolymers

A practical and simple method for the preparation of ABA-type olefin triblock copolymers, e.g., PE-b-poly(ethylene-co-propylene)-b-PE, has been described. The performance of the so-called “coordinative chain transfer polymerization” (CCTP) by sequential feed of ethylene and ethylene/propylene mixed gas generated a Zn-bound diblock copolymer (i.e., (PE-b-poly(ethylene-co-propylene)yl)2Zn). Treatment of the Zn-bound diblock copolymer with lauroyl peroxide (CH3(CH2)10C(O)O-OC(O)(CH2)10CH3) led to a C(sp3)–C(sp3) coupling reaction between the two diblock chains bound on the zinc site and an ABA-type olefin triblock copolymer, PE-b-poly(ethylene-co-propylene)-b-PE, was formed. Upon the treatment with lauroyl peroxide, the number-average molecular weight increased by 1.5–1.7 times. The occurrence of the coupling reaction was verified using a model compound, (Oct)2Zn. The ABA-type triblock copolymer exhibited thermoplastic elastomeric properties and dramatically improved mechanical properties (twice the tensile ...

Dialkenylmagnesium Compounds in Coordinative Chain Transfer Polymerization of Ethylene. Reversible Chain Transfer Agents and Tools To Probe Catalyst Selectivities toward Ring Formation

A range of dialkenylmagnesium compounds ([CH2═CH(CH2)n]2Mg; n = 1–6) were synthesized and used as chain transfer agents (CTA) with either (C5Me5)2NdCl2Li(OEt2)2 (1) or [Me2Si(C13H8)2Nd(BH4)2Li(thf)]2 (2) neodymium precursors for the polymerization of ethylene. In all cases, the systems followed a controlled coordinative chain transfer polymerization mechanism. The intramolecular insertion of the vinyl group on the CTA in growing chains is possible and led to the formation of cyclopentyl, cyclohexyl, and possibly cycloheptyl chain ends. While the production of cyclopentyl- or cyclohexyl-capped polyethylene chains can be quantitative (n = 2–5), the integrity of this double bond can also be kept if n is higher than 6. In comparison to 1/CTA catalytic systems, 2/CTA catalytic systems showed a higher propensity to produce cycloalkyl chain ends. This was ascribed to the lower steric demand around the active site, as shown by DFT calculations. In addition, the formation of bis(cyclopentylmethyl)magnesium from di...