Biaxial Chain Growth of Polyolefin and Polystyrene from 1,6-Hexanediylzinc Species for Triblock Copolymers

New Thermoplastic Elastomers based on Ethylene-Butadiene-Rubber (EBR) by Switching from Anionic to Coordinative Chain Transfer Polymerization

Olefin triblock copolymers based on glassy polystyrene (PS), ethylene butadiene rubber (EBR) and highly crystalline polyethylene (PE) segments were prepared for the first time using a switch strategy from anionic polymerization to coordinative chain transfer (co)polymerization (CCT(co)P). PS chains obtained by anionic polymerization were transmetalated with mesitylmagnesium bromide (BrMgMes) to act as macromolecular chain transfer agents (macro-CTA, PS-MgMes) in the CCTcoP of ethylene and butadiene using {Me2Si(C13H8)2Nd(BH4)2Li(THF)}2 complex (1). Further chain extension by CCTP using pure ethylene in the monomer feed afforded well-defined PS-b-EBR-b-PE triblock copolymers. The structural, rheological and mechanical properties of these materials demonstrate excellent balance between properties and easy processability at moderate temperatures (>150 °C). We demonstrate that such triblock copolymers behave effectively as low-viscosity PS-b-EBR diblock copolymers above the melting point of PE domains and high performance thermoplastic elastomers (TPEs) upon crystallization of PE segments.

Synthesis of Telechelic Isotactic Polypropylenes for Circular Polypropylene-like Materials via Chain Transfer Polymerization

While synthesizing circular polymers with telechelic polyolefin building blocks recently emerged as a promising strategy for addressing conventional polyethylenes' sustainability challenges, the lack of telechelic iPP (tPP) with sufficient difunctional purity for polycondensation has been limiting the development of circular polypropylenes with iPP-like structures and properties. Here we described a combined approach of coordinative chain transfer polymerization and transition-metal-catalyzed quenching reaction with various acyl chlorides, affording tPPs with a high difunctional ratio (up to ∼99%) and broad end functional group scope. The steric effect of polymeryl-Zn species and the role of Pd catalyst were revealed by DFT. This method also solved the low difunctional ratio challenge for telechelic polyethylenes. Ester-linked iPPs with iPP-like structure and thermomechanical properties and PE/iPP multiblock copolymers were synthesized by the resulting tPPs.

Accessing Functionalized Ultra-High Molecular Weight Poly(α-olefin)s via Hafnium-Mediated Highly Isospecific Copolymerization

Inspired by the favorable impact of heteroatom-containing groups in phenoxy-imine titanium and late transition metal catalysts, a series of novel pyridylamido hafnium catalysts bearing ─OMe (Cat-OMe), ─CF3 (Cat-CF3), and ─C6F5 (Cat-C6F5) substituents are designed and synthesized. Together with the established hafnium catalysts Cat-H and Cat-iPr by Dow/Symyx, these catalysts are applied in the polymerization of α-olefins, including 1-hexene, 1-octene, and 4M1P, as well as in the copolymerization of these α-olefins with a specifically designed polar monomer. The enhancement of polymer molecular weight derived from catalyst modification and the incorporation of polar monomers is discussed in detail. Notably, the new catalysts are all highly active for α-olefins polymerization, with catalyst Cat-CF3 producing isotactic polymers with the highest molecular weight (Mw = 1649 kg mol-1); in copolymerization with polar monomers, catalyst Cat-OMe yields isotactic copolymer with the highest molecular weight (Mw = 2990 kg mol-1). Interestingly, catalyst Cat-C6F5 bearing a ─C6F5 group in the N-aryl moiety gives rise to poly(α-olefin) with reduced stereoselectivity. The findings of this study underscore the potential of heteroatom-containing groups in the development of early transition metal catalysts and the synthesis of polymer with novel structures.

Coordinative Chain Transfer and Chain Shuttling Polymerization

Coordinative chain transfer polymerization, CCTP, is a degenerative chain transfer polymerization process that has a wide range of applications. It allows a highly controlled synthesis of polyolefins, stereoregular polydienes, and stereoregular polystyrene, including (stereo)block as well as statistical copolymers thereof. It also shows a green character by allowing catalyst economy during the synthesis of such polymers. CCTP notably allows the end functionalization of both the commodity and stereoregular specialty polymers aforementionned, control of the composition of statistical copolymers without adjusting the feed, and quantitative formation of 1-alkenes from ethene. A one-pot one-step synthesis of the original multiblock microstructures and architectures by chain shuttling polymerization (CSP) is also an asset of CCTP. This methodology takes advantage of the simultaneous presence of two catalysts of different selectivity toward comonomers that produce blocks of different composition/microstructure, while still allowing the chain transfer. This affords the production of highly performant functional polymers, such as thermoplastic elastomers and adhesives, among others. This approach has been extended to cyclic esters' and ethers' ring-opening polymerization, providing new types of multiblock microstructure. The present Review provides the state of the art in the field with a focus on the last 10 years.

Multiblock Copolymers Based on Highly Crystalline Polyethylene and Soft Poly(ethylene-co-butadiene) Segments: Towards Polyolefin Thermoplastic Elastomers

Block copolymers based on polyethylene (PE) and ethylene butadiene rubber (EBR) were obtained by successive controlled coordinative chain transfer polymerization (CCTP) of a mixture of ethylene and butadiene (80/20) and pure ethylene. EBR-b-PE diblock copolymers were synthesized using the {Me2 Si(C13 H8 )2 Nd(BH4 )2 Li(THF)}2 complex in combination with n-butyl,n-octyl magnesium (BOMAG) used as both the alkylating and chain transfer agent (CTA). Triblock and multiblock copolymers featuring highly semi-crystalline PE hard segments and soft EBR segments were further obtained by the development of a bimetallic CTA, the pentanediyl-1,5-di(magnesium bromide) (PDMB). These new block copolymers undergo crystallization-driven organization into lamellar structures and exhibit a variety of mechanical properties, including excellent extensibility and elastic recovery in the case of triblock and multiblock copolymers.

Selective deuteration along a polyethylene chain: Differentiating conformation segment by segment

To improve the circularity and performance of polyolefin materials, recent innovations have enabled the synthesis of polyolefins with new structural features such as cleavable breakpoints, functional chain ends, and unique comonomers. As new polyolefin structures become synthetically accessible, fundamental understanding of the effects of structural features on polymer (re)processing and mechanical performance is increasingly important. While bulk material properties are readily measured through conventional thermal or mechanical techniques, selective measurement of local material properties near structural defects is a major characterization challenge. Here, we synthesized a series of polyethylenes with selectively deuterated segments using a polyhomologation approach and employed vibrational spectroscopy to evaluate crystallization and melting of chain segments near features of interest (e.g., end groups, chain centers, and mid-chain structural defects). Chain-end functionality and defects were observed to strongly influence crystallinity of adjacent deuterated chain segments. Additionally, chain-end crystallinity was observed to have different molar mass dependence than mid-chain crystallinity. The synthesis and spectroscopy techniques demonstrated here can be applied to range of previously inaccessible deuterated polyethylene structures to provide direct insight into local crystallization behavior.

Up-Scale Synthesis of p-(CH2=CH)C6H4CH2CH2CH2Cl and p-ClC6H4SiR3 by CuCN-Catalyzed Coupling Reactions of Grignard Reagents with Organic Halides

Grignard reagents featuring carbanion characteristics are mostly unreactive toward alkyl halides and require a catalyst for the coupling reaction. With the need to prepare p-(CH₂=CH)C₆H₄CH₂CH₂CH₂Cl on a large scale, the coupling reaction of p-(CH₂=CH)C₆H₄MgCl with BrCH₂CH₂CH₂Cl was attempted to screen the catalysts, and CuCN was determined to be the best catalyst affording the desired compound in 80% yield with no formation of Wurtz coupling side product CH₂=CHC₆H₄-C₆H₄CH=CH₂. The p-(CH₂=CH)C₆H₄Cu(CN)MgCl species was proposed as an intermediate based on the X-ray structure of PhCu(CN)Mg(THF)₄Cl. p-ClC₆H₄MgCl did not react with sterically encumbered R₃SiCl (R = n-Bu or n-octyl). However, the reaction took place with the addition of 3 mol % CuCN catalyst, affording the desired compound p-ClC₆H₄SiR₃. The structures of p-(CH₂=CH)C₆H₄CH₂CH₂CH₂MgCl and p-ClC₆H₄MgCl were also elucidated, which existed as an aggregate with MgCl₂, suggesting that some portion of the Grignard reagents were possibly lost in the coupling reaction due to coprecipitation with the byproduct MgCl₂. R₃SiCl (R = n-Bu or n-octyl) was also prepared easily and economically with no formation of R₄Si when SiCl₄ was reacted with 4 equiv of RMgCl. Using the developed syntheses, [p-(CH₂=CH)C₆H₄CH₂CH₂CH₂]₂Zn and iPrN[P(C₆H₄-p-SiR₃)₂]₂, which are potentially useful compounds for the production of PS-block-PO-block-PS and 1-octene, respectively, were efficiently synthesized with substantial cost reductions.

Highly Versatile Strategy for the Production of Telechelic Polyolefins

A general and versatile synthetic strategy for producing practical quantities of a wide range of phenyl-group-terminated hetero- and homotelechelic semicrystalline polyethenes and amorphous atactic and semicrystalline isotactic poly(α-olefins) is reported. The phenyl groups serve as synthons for functionalities of additional classes of telechelic polyolefins that can be "unmasked" through simple high yielding postpolymerization reactions. A demonstration of the value of these materials as building blocks for structural classes of polyolefin-based synthetic polymers was provided by syntheses of well-defined polyolefin-polyester di- and triblock copolymers that were shown to adopt microphase-segregated nanostructured mesophases in the condensed phase.

Cyclic olefin copolymers containing both linear polyethylene and poly(ethylene-co-norbornene) segments prepared from chain shuttling copolymerization of ethylene and norbornene

A series of novel HDPE/COC multiblock copolymers have been effectively obtained via chain shuttling copolymerization of ethylene and NBE. These promising copolymers exhibit excellent clarity, high heat resistance and balanced mechanical properties.

Design of selective divalent chain transfer agent for coordinative chain transfer polymerization of ethylene and its copolymerization with butadiene

PhMg(CH2)5MgPh and MesMg(CH2)5MgMes – divalent bis-metalated chain transfer agents (CTA) – were designed, synthesized and implemented in the polymerization of ethylene or the copolymerization of ethylene with butadiene mediated by...

Temporal Control over Two- and Three-State Living Coordinative Chain Transfer Polymerization for Modulating the Molecular Weight Distribution Profile of Polyolefins

A highly versatile new strategy for manipulating the molecular weight profiles, including breadth, asymmetry (skewness) and modal nature (mono-, bi-, and multimodal), of a variety of different polyolefins is reported. It involves temporal control over two- and three-state living coordinative chain transfer polymerization (LCCTP) of olefins in a programmable way. By changing the identity of the R' groups of the chain transfer agent, ER'_n , with time, different populations of chains within a bi- or multimodal polyolefin product can be selectively tagged with different end-groups. By changing the nature of the main-group metal of the CTA, programmed manipulation of the relative magnitudes of the dispersities of the different maxima that make up the final MWD profile can be achieved. This strategy can be implemented with existing LCCTP materials and conventional reactor methods to provide access to scalable and practical quantities of an unlimited array of new polyolefin materials.

Hybridization of Step-/Chain-Growth and Radical/Cationic Polymerizations Using Thioacetals as Key Components for Triblock, Periodic and Random Multiblock Copolymers with Thermoresponsiveness

A novel strategy for synthesizing a series of multiblock copolymers is developed by combining radical/cationic step-growth polymerizations of dithiols and divinyl ethers and chain-growth cationic degenerative chain-transfer (DT) polymerizations of vinyl ethers using thioacetals as key components. The combination of radical step-growth polymerization and a cationic thiol-ene reaction or cationic step-growth polymerization enables the synthesis of a series of macro chain-transfer agents (CTAs) composed of poly(thioether) and thioacetal groups at different positions. The resulting products are 1) bifunctional macro CTAs with thioacetal groups at both chain ends, 2) periodic macro CTAs periodically having thioacetal groups in the main chain, and 3) random macro CTAs randomly having thioacetal groups in the main chain. Subsequently, the obtained macro CTAs are used for chain-growth cationic DT polymerization of methoxyethyl vinyl ether (MOVE) to result in 1) triblock, 2) periodic, and 3) random multiblock copolymers consisting of poly(thioether) and poly(MOVE) segments. All these triblock and multiblock copolymers composed of hydrophobic poly(thioether) and hydrophilic poly(MOVE) segments show an amphiphilic tendency to form characteristic micelles in aqueous solutions. In addition, due to the thermoresponsive poly(MOVE) segments, the obtained copolymers exhibit lower critical solution temperatures that depend on the segment sequences and lengths.

Synthesis of telechelic polyolefins

A comprehensive review of all the methodologies developed for the synthesis of telechelic polyolefins is reported.

Preparation of Pyridylamido Hafnium Complexes for Coordinative Chain Transfer Polymerization

The pyridylamido hafnium complex (I) discovered at Dow is a flagship catalyst among postmetallocenes, which are used in the polyolefin industry for PO-chain growth from a chain transfer agent, dialkylzinc. In the present work, with the aim to block a possible deactivation process in prototype compound I, the corresponding derivatives were prepared. A series of pyridylamido Hf complexes were prepared by replacing the 2,6-diisopropylphenylamido part in I with various 2,6-R2C6H3N-moieties (R = cycloheptyl, cyclohexyl, cyclopentyl, 3-pentyl, ethyl, or Ph) or by replacing 2-iPrC6H4C(H)- in I with the simple PhC(H)-moiety. The isopropyl substituent in the 2-iPrC6H4C(H)-moiety influences not only the geometry of the structures (revealed by X-ray crystallography), but also catalytic performance. In the complexes bearing the 2-iPrC6H4C(H)-moiety, the chelation framework forms a plane; however, this framework is distorted in the complexes containing the PhC(H)-moiety. The ability to incorporate α-olefin decreased upon replacing 2-iPrC6H4C(H)-with the PhC(H)-moiety. The complexes carrying the 2,6-di(cycloheptyl)phenylamido or 2,6-di(cyclohexyl)phenylamido moiety (replacing the 2,6-diisopropylphenylamido part in I) showed somewhat higher activity with greater longevity than did prototype catalyst I.

Polystyrene Chain Growth Initiated from Dialkylzinc for Synthesis of Polyolefin-Polystyrene Block Copolymers

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.

One-pot syntheses of heterotelechelic α-vinyl,ω-methoxysilane polyethylenes and condensation into comb-like and star-like polymers with high chain end functionality

Crystalline and functional comb-like and star-like polyethylene architectures.

Effect of boundary chain folding on thermal conductivity of lamellar amorphous polyethylene

Thermal transport properties of amorphous polymers depend significantly on the chain morphology, and boundary chain folding is a common phenomenon in bulk or lamellar polymer materials. In this work, by using molecular dynamics simulations, we study thermal conductivity of lamellar amorphous polyethylene (LAPE) with varying chain length (L 0). For a short L 0 without boundary chain folding, thermal conductivity of LAPE is homogeneous along the chain length direction. In contrast, boundary chain folding takes place for large L 0, and the local thermal conductivity at the boundary is notably lower than that of the central region, indicating inhomogeneous thermal transport in LAPE. By analysing the chain morphology, we reveal that the boundary chain folding causes the reduction of both the orientation order parameter along the heat flow direction and the radius of gyration, leading to the reduced local thermal conductivity at the boundary. Further vibrational spectrum analysis reveals that the boundary chain folding shifts the vibrational spectrum to the lower frequency, and suppresses the transmission coefficient for both C-C vibration and C-H vibration. Our study suggests that the boundary chain folding is an important factor for polymers to achieve desirable thermal conductivity for plastic heat exchangers and electronic packaging applications.

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 [N^amido,N,C^aryl]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.

Preparation of Pincer Hafnium Complexes for Olefin Polymerization

Pincer-type [Cnaphthyl, Npyridine, Namido]HfMe2 complex is a flagship among the post-metallocene catalysts. In this work, various pincer-type Hf-complexes were prepared for olefin polymerization. Pincer-type [Namido, Npyridine, Namido]HfMe2 complexes were prepared by reacting in situ generated HfMe4 with the corresponding ligand precursors, and the structure of a complex bearing 2,6-Et2C6H3Namido moieties was confirmed by X-ray crystallography. When the ligand precursors of [(CH3)R2Si-C5H3N-C(H)PhN(H)Ar (R = Me or Ph, Ar = 2,6-diisopropylphenyl) were treated with in situ generated HfMe4, pincer-type [Csilylmethyl, Npyridine, Namido]HfMe2 complexes were afforded by formation of Hf-CH2Si bond. Pincer-type [Cnaphthyl, Sthiophene, Namido]HfMe2 complex, where the pyridine moiety in the flagship catalyst was replaced with a thiophene unit, was not generated when the corresponding ligand precursor was treated with HfMe4. Instead, the [Sthiophene, Namido]HfMe3-type complex was obtained with no formation of the Hf-Cnaphthyl bond. A series of pincer-type [Cnaphthyl, Npyridine, Nalkylamido]HfMe2 complexes was prepared where the arylamido moiety in the flagship catalyst was replaced with alkylamido moieties (alkyl = iPr, cyclohexyl, tBu, adamantyl). Structures of the complexes bearing isopropylamido and adamantylamido moieties were confirmed by X-ray crystallography. Most of the complexes cleanly generated the desired ion-pair complexes when treated with an equivalent amount of [(C18H37)2N(H)Me]+[B(C6F5)4]-, which showed negligible activity in olefin polymerization. Some complexes bearing bulky substituents showed moderate activities, even though the desired ion-pair complexes were not cleanly afforded.

Polystyrene Chain Growth from Di-End-Functional Polyolefins for Polystyrene-Polyolefin-Polystyrene Block Copolymers

Triblock copolymers of polystyrene (PS) and a polyolefin (PO), e.g., PS-block-poly(ethylene-co-1-butene)-block-PS (SEBS), are attractive materials for use as thermoplastic elastomers and are produced commercially by a two-step process that involves the costly hydrogenation of PS-block-polybutadiene-block-PS. We herein report a one-pot strategy for attaching PS chains to both ends of PO chains to construct PS-block-PO-block-PS directly from olefin and styrene monomers. Dialkylzinc compound containing styrene moieties ((CH₂=CHC₆H₄CH₂CH₂)₂Zn) was prepared, from which poly(ethylene-co-propylene) chains were grown via "coordinative chain transfer polymerization" using the pyridylaminohafnium catalyst to afford di-end functional PO chains functionalized with styrene and Zn moieties. Subsequently, PS chains were attached at both ends of the PO chains by introduction of styrene monomers in addition to the anionic initiator Me₃SiCH₂Li·(pmdeta) (pmdeta = pentamethyldiethylenetriamine). We found that the fraction of the extracted PS homopolymer was low (~20%) and that molecular weights were evidently increased after the styrene polymerization (ΔM_n = 27⁻54 kDa). Transmission electron microscopy showed spherical and wormlike PS domains measuring several tens of nm segregated within the PO matrix. Optimal tensile properties were observed for the sample containing a propylene mole fraction of 0.25 and a styrene content of 33%. Finally, in the cyclic tensile test, the prepared copolymers exhibited thermoplastic elastomeric properties with no breakage up over 10 cycles, which is comparable to the behavior of commercial-grade SEBS.