Polar Vinyl Monomers Research Articles

Highly Tolerant Living/Controlled Anionic Polymerization of Dialkyl Acrylamides Enabled by Zinc Triflate/Phosphine Lewis Pair.

Living polymerizations of polar vinyl monomers have been successful for decades. However, they still suffer the following challenges: fast propagation, air-moisture tolerance, and negligible side reactions even at elevated temperatures. Here, we developed an unprecedented polymerization that overcomes these limitations using a Lewis pair catalyst. The anionic polymerization of dialkyl acrylamides proceeded in a living/controlled matter using Zn(OTf)2/PPh3 within a wide temperature range of 25-100 °C for short times (1-10 min) even under open-air conditions. The recovery and reuse of Zn(OTf)2 without loss of polymerization activity were observed to be possible. The polymerization was retarded by excess Zn(OTf)2, the additive methanol, and water, indicating equilibriums of the propagating species with them. The putative propagating zinc triflate-ate complex was tolerant to the protic additives and significantly selective for the propagation.

Nickel‐ and Palladium‐Catalyzed Copolymerizations of Norbornene with Polar α‐Olefins

AbstractRecent progress regarding the copolymerization of norbornene with various polar α‐olefins catalyzed by nickel and palladium catalysts is reviewed here with special attention paid to the diverse catalyst frameworks, polar monomer scopes as well as polymer microstructures. Both the influences of steric effect and electron property of ligand substituents and the type of polar monomers on the catalytic behaviors (activity, stability, polarity tolerance, etc.) and the polymer microstructures (molecular weight and distribution, comonomer contents, etc.) have been summarized. The introduction of noncyclic‐olefins, such as polar vinyl monomers, polar higher α‐olefins, and polar styrenes, into rigid cyclic‐based polynorbornene chain resulted in significant modifications on the polarity, compatibility, thermostability, processibility, transparency, and many other properties of the material, which has also been discussed in the review. The contents of this review have been classified according to the type of polar monomers involved in the norbornene copolymerization, and each section included nickel and palladium catalysts bearing different ligand structures, which will be meaningful for the development of new types of catalysts and new families of norbornene‐based cyclic olefin copolymer materials in the future.

Theoretical studies on the regioselectivity of polar vinyl monomer insertion catalyzed by an α-diimine Pd(ii) complex

This study uses DFT to investigate the regioselectivity of PVM insertion with the DBB–Ipty α-diimine Pd(ii) complex. It combines DFT with MLR analysis to identify key factors influencing regioselectivity in the reaction.

Inorganic Chemistry in Dalian University of Technology: Fundamental Science and Solution for Renewable Energy, Environment, Health, and Materials

Inorganic Chemistry in Dalian University of Technology: Fundamental Science and Solution for Renewable Energy, Environment, Health, and Materials

Polar Group-Promoted Copolymerization of Ethylene with Polar Olefins

Copolymerization of ethylene (E) and polar vinyl monomers is a great challenge but remains attractive, especially for early transition metal catalysts featuring strong oxophilicity. Herein, we present the copolymerization of E with 6-phenoxy-1-hexene (POH) by scandium precatalysts with different steric hindrances: (FluCH2CH2NHC)Sc(CH2SiMe3)2 (1), (FluCH2C5H4N)Sc(CH2SiMe3)2 (2), (FluCH2Ph)Sc(CH2SiMe3)2(THF) (3), and (C5Me4Ph)Sc(CH2C6H4NMe2-o)2 (4). In comparable conditions, precatalyst 1, activated by [Ph3C][B(C6F5)4] and AliBu3, shows high activity (1.4 × 105 g molSc–1 h–1) but gives a low POH incorporation ratio of 0.7 mol %. Under identical conditions, the activity of 2 drops to 0.1 × 105 g molSc–1 h–1. In contrast, the half-sandwich scandium precatalyst 3 displays a much higher activity (8.1 × 105 g molSc–1 h–1) and affords a copolymer with 7.0 mol % POH. The highest activity (18.0 × 105 g molSc–1 h–1) and incorporation ratio (8.6 mol %) are achieved by 4. After optimization of the reaction conditions, up to 16 mol % of POH could be incorporated into the copolymer produced with 4. The resultant copolymers are readily transformed into brominated products and, subsequently, ethylene-based ionomers featuring excellent mechanical properties. Density functional theory (DFT) simulations are employed to illustrate the mechanisms of polar group incorporation and the control of activity from kinetic, thermodynamic, and geometric viewpoints.

Stereoselective Polymerization of Aromatic Vinyl Polar Monomers

AbstractPolar vinyl polymers, a class of polymers with polar groups as side chains, have significant advantages over conventional nonpolar polyolefin materials in terms of viscosity, toughness, interfacial properties (dyeability and printability), and compatibility with solvents or other polymers. Among them, aromatic polar vinyl polymers are of interest because of their good heat resistance properties. In addition, stereoselective polymerization of aromatic polar vinyl monomers has been rapidly developed because the steric structure of the polymer has a significant impact on its physical properties. In this paper, we review the research progress of stereoselective polymerization catalysts for aromatic polar vinyl monomers in recent years, discuss in detail the influence of ligand structure, electronic effect of substituents, spatial site resistance effect, central rare earth metal species and polymerization solvents on the activity and stereoselectivity of polymerization reactions, and explore the possible mechanism of polymerization reaction.

Compounded Interplay of Kinetic and Thermodynamic Control over Comonomer Sequences by Lewis Pair Polymerization.

The design of facile synthetic routes to well-defined block copolymers (BCPs) from direct polymerization of one-pot comonomer mixtures, rather than traditional sequential additions, is both fundamentally and technologically important. Such synthetic methodologies often leverage relative monomer reactivity toward propagating species exclusively and therefore are rather limited in monomer scope and control over copolymer structure. The recently developed compounded sequence control (CSC) by Lewis pair polymerization (LPP) utilizes synergistically both thermodynamic (Keq) and kinetic (kp) differentiation to precisely control BCP sequences and suppress tapering and misincorporation errors. Here, we present an in-depth study of CSC by LPP, focusing on the complex interplay of the fundamental Keq and kp parameters, which enable the unique ability of CSC-LPP to precisely control comonomer sequences across a variety of polar vinyl monomer classes. Individual Lewis acid equilibrium and polymerization rate parameters of a range of commercially relevant monomers were experimentally quantified, computationally validated, and rationalized. These values allowed for the judicious design of copolymerizations which probed multiple hypotheses regarding the constructive vs conflicting nature of the relationship between Keq and kp biases, which arise during CSC-LPP of comonomer mixtures. These relationships were thoroughly explored and directly correlated with resultant copolymer microstructures. Several examples of higher-order BCPs are presented, further demonstrating the potential for materials innovation offered by this methodology.

Copolymerization of Ethylene and Methyl Acrylate by Dibenzocycloheptyl-Substituted Aryliminopyridyl Ni(II) Catalysts

Copolymerization of ethylene with polar vinyl monomers to yield functionalized and possibly easier recyclable polyolefins is challenging and it is currently being pursued mainly using expensive Pd-based catalysts. Herein, the copolymerization of ethylene and methyl acrylate (MA) is achieved by the dibenzocycloheptyl-substituted aryliminopyridyl Ni(II) complexes, affording copolymers with selectively in-chain incorporated MA units as well as both in-chain and end-of-chain inserted MA units depending on the catalyst structure and the reaction conditions

Vinyl-addition polymerizations of norbornene and methyl methacrylate by the palladium(II) complexes ligated by 2-iminomethylquinoline and 2-iminomethylpyridine derivatives

Novel Pd(II) complexes, namely, [LnPdCl2] (Ln = LA and LB), where LA is (E)-3-methoxy-N-(quinolin-2-ylmethylene)propan-1-amine and LB is (E)-N-(pyridin-2-ylmethylene)hexan-1-amine, were synthesized and characterized. X-ray diffraction studies revealed distorted square planar geometries around the Pd(II) center in [LnPdCl2] (Ln = LA and LB). The catalytic capabilities of the synthesized complexes were tested in vinyl addition polymerization of norbornene (NB) in the presence of the cocatalyst modified methylaluminoxane (MMAO), displaying high activities with conversions ≥ 94% in chlorobenzene at 25 °C. The complex [LBPdCl2] displayed the highest activity of up to 4.40 × 106 gPNBmolPd−1h−1 at 25 °C, generating insoluble polynorbornene (PNB) at an NB/Al/Pd ratio of 8,000:500:1. In addition, preliminary methyl methacrylate (MMA) polymerization studies of the [LnPdCl2]/MMAO system demonstrated that the activities toward polar vinyl monomer production were in the range of 8.00 × 104 to 8.20 × 104gPMMAmolPd−1h−1 at 60 °C, yielding a high-molecular-weight syndiotactic poly(methyl methacrylate) (PMMA, Mw = 1.89 × 106gmol−1).

Copolymerization of ethylene with non-vinyl polar monomers.

Introduction of functional groups on polyethylene endows it with a higher surface property and thus various catalysts have been developed for the copolymerization of ethylene with polar vinyl monomers. Aside from vinyl monomers, however, other classes of polar monomers have not found application in the copolymerization with ethylene. Here, in this short review article, our latest studies on catalyst development aiming at the use of non-vinyl polar monomers and the properties of the resulting copolymers are summarized.

Tunable “In-Chain” and “At the End of the Branches” Methyl Acrylate Incorporation in the Polyolefin Skeleton through Pd(II) Catalysis

The synthesis of functionalized polyolefins through coordination–insertion polymerization is a highly challenging reaction. The ideal catalyst, in addition to showing a high productivity, has to be able to control the copolymer microstructure and, in particular, the way of the polar vinyl monomer incorporation. In this contribution, we modified the typical Brookhart’s catalyst by introducing in the fourth coordination site of palladium a hemilabile, potentially bidentate ligand, such as a thiophenimine (N–S). The obtained cationic Pd(II) complexes, [Pd(Me)(N–N)(N–S)][PF6], generated active catalysts for the ethylene/methyl acrylate (MA) copolymerization leading to the desired copolymer with a different incorporation of the polar monomer depending on both the reaction medium and the N–S ligand. Surprisingly enough, the produced copolymers have the inserted acrylate both at the end of the branches (T(MA)) and in the main chain (M(MA)) in a ratio M(MA)/T(MA) that goes from 9:91 to 45:55 moving from dichloromethane to trifluoroethanol (TFE) as a solvent for the catalysis and varying the N–S ligand. The catalytic behavior of the new complexes was compared to that of the parent compound [Pd(Me)(N–N)(MeCN)][PF6], highlighting the fact that when the copolymerization is carried out in trifluoroethanol, this complex is also able to produce the E/MA copolymer with MA inserted both in the main chain and at the end of the branches. Accurate NMR studies on the reactivity of the precatalyst [Pd(Me)(N–N)(MeCN)][PF6] with the two comonomers allowed us to discover that in the fluorinated solvent, the catalyst resting state is an open-chain intermediate having both the organic fragment, originated from the migratory insertion of MA into the Pd–Me bond, and the acetonitrile coordinated to palladium and not the six-membered palladacycle typically observed for the Pd-α-diimine catalysts. This discovery is also supported by both DFT calculations and in situ NMR studies carried out on [Pd(Me)(N–N)(N–S)][PF6] complexes that point out that N–S remains in the palladium coordination sphere during catalysis. The open-chain intermediate is responsible for the growth of the copolymer chain with the polar monomer inserted into the main chain.

Mechanism of Spatial and Temporal Control in Precision Cyclic Vinyl Polymer Synthesis by Lewis Pair Polymerization

In typical cyclic polymer synthesis via ring-closure, chain growth and cyclization events are competing with each other, thus affording cyclic polymers with uncontrolled molecular weight or ring size and high dispersity. Here we uncover a mechanism by which Lewis pair polymerization (LPP) operates on polar vinyl monomers that allows the control of where and when cyclization takes place, thereby achieving spatial and temporal control to afford precision cyclic vinyl polymers or block copolymers with predictable molecular weight and low dispersity (≈1.03). A combined experimental and theoretical study demonstrates that cyclization occurs only after all monomers have been consumed (when) via conjugate addition of the propagating chain end to the specific site of the initiating chain end (where), allowing the cyclic polymer formation steps to be regulated and executed with precision in space and time.

Lewis Pair RAFT Polymerization of Methacrylates on-Water: Evidence of Radical Propagation Mechanism

Abstract The Lewis pair (LP) composed of PPh3 and Cu(OTf)2 on-water is a newly emerging catalytic system for polymerization of polar vinyl monomers. Herein, we report the additive effect of the reversible addition–fragmentation chain transfer (RAFT) agents on the polymerization of six methacrylate monomers with various hydrophilicities. The polymerization control by the RAFT agents proved that this LP polymerization involves a radical propagating mechanism.

Facile Access to Polar-Functionalized Ultrahigh Molecular Weight Polyethylene at Ambient Conditions

Facile Access to Polar-Functionalized Ultrahigh Molecular Weight Polyethylene at Ambient Conditions

Palladium Promoted Copolymerization of Carbon Monoxide with Polar or Non-polar Olefinic Monomers

The copolymers of carbon monoxide (CO) and olefins, namely polyketones, are a family of widely used materials. In the catalytic preparation of these materials, palladium(II) catalysts represent the most successful catalytic systems. The production of both alternating and non-alternating polyketones has been achieved, with a great difference in their physical properties. Herein, a variety of palladium(II) catalysts, employed for the copolymerization of CO with various olefinic monomers, such as ethylene, α -olefins, styrene and polar vinyl monomers, are fully summarized. The influence of important factors, such as solvents and counterions on specific copolymerization, is also discussed. This review aims to enlighten the design of new Pd catalysts with improved properties, as well as the development of new polyketone materials.

Homo- and copolymerization of norbornene using tridentate IzQO palladium catalysts with dimethylaminoethyl as a side arm

Rigid IzQO–Pd catalysts were synthesized by Rh(iii)-catalyzed C–H/alkyne annulation and applied for the homo- and copolymerizations of norbornene with polar vinyl monomers.

Selective, Catalytic Oxidations of C–H Bonds in Polyethylenes Produce Functional Materials with Enhanced Adhesion

Summary The synthesis of functional and processable polyethylenes from simple vinyl monomers with controlled molecular weights and architectures has been a grand challenge of polymer chemistry. Post-polymerization modification of the homopolymers of ethylene is attractive for this purpose but has been hampered by the lack of efficient methods for the selective functionalization of C–H bonds in polyolefins. We report the selective, catalytic oxidation of C–H bonds in commodity polyethylenes with varying molecular weights and architectures. Remarkably, the functionalized materials, even at low levels of functionalization, exhibit physical properties that are absent in unmodified polyolefins, such as strong adhesion and the ability to be painted with common waterborne latex paint. Such observations indicate that selectively modified polyethylenes as described here may help to transform existing commodity plastics into more valuable and potentially more sustainable materials.

Neutral Nickel(II) Catalysts: From Hyperbranched Oligomers to Nanocrystal-Based Materials

ConspectusPlastics materials are a vital component of modern technologies. They are applied, e.g., in construction, transportation, communication, water supply, or health care. Consequently, polyolefins-the most important plastics by scale-are produced in vast amounts by catalytic polymerization. Effective and selective as the catalysts used may be, their high sensitivity toward any polar compounds limits these methods to hydrocarbon reaction media and monomers like ethylene and propylene, respectively. This can be overcome by less oxophilic late transition metal catalysts, and here particularly neutral nickel(II) catalysts have seen major advances in the past few years. They stand out due to being capable of aqueous catalytic polymerizations. Aqueous polymerizations are benign processes that advantageously yield polymers in the form of particles. Moreover, these catalysts can incorporate polar monomers like acrylates, a realm previously restricted to noble metal catalysts. The introduction of polar moieties can induce properties like compatibility with metals or fibers in high performance composite materials or a desirable degradability.This Account provides a personal account of developments in the past decade. Prior findings are outlined briefly as a background. Aqueous polymerizations afford unique polyethylene morphologies as a result of the unusual underlying particle growth mechanism. Polymer single crystals are formed, which can be composed of a single ultrahigh molecular weight chain. This represents a completely disentangled state of such extremely long polymer chains, which has been long sought-after in order to overcome the difficult processing of high performance ultrahigh molecular weight materials. A key prerequisite for this approach and utilization of these catalysts, in general, is control of polymer branching and molecular weight. This is achieved via remote substituents on the Ni(II)-chelating ligand. Despite their distal position to the active site, weak secondary interactions control whether branching and chain transfer pathways compete very effectively with chain growth or are suppressed entirely. This provides access to hyperbranched oligomers, on the one hand, and enables living polymerizations to strictly linear high molecular weight polymer, on the other hand. Other advanced catalysts provide linear copolymers with in-chain polar monomer repeat units for the first time with non-noble metal active sites. Mechanistic studies further revealed that for copolymerizations with polar vinyl monomers the decisive limiting factor is irreversible termination reactions with neutral Ni(II) catalysts, rather than the well-recognized reversible blocking of coordination sites by the polar functional groups found for other types of catalysts. The mechanistic picture also implies the possibility of free-radical pathways, and their role in the formation of desirable polymer end groups and polymer blends is now being recognized. The area of neutral Ni(II) catalysts has progressed significantly in the entire range from fundamental mechanistic understanding, catalyst performance, and previously inaccessible polymer microstructures, and it is moving forward to materials through unique concepts. The unprecedented ability to incorporate functional groups into linear crystalline polyethylene also provides perspectives for much needed polyolefin materials that will not persist in the natural environment for several decades but that can be degraded by virtue of low levels of functional groups.

Rare-Earth Metal Complexes-Mediated Stereoselective Polymerization of Aromatic Polar Vinyl Monomers

Rare-Earth Metal Complexes-Mediated Stereoselective Polymerization of Aromatic Polar Vinyl Monomers

Mechanistic Insight into the Stereoselective Cationic Polymerization of Vinyl Ethers.

The control of the tacticity of synthetic polymers enables the realization of emergent physical properties from readily available starting materials. While stereodefined polymers derived from nonpolar vinyl monomers can be efficiently prepared using early transition metal catalysts, general methods for the stereoselective polymerization of polar vinyl monomers remain underdeveloped. We recently demonstrated asymmetric ion pairing catalysis as an effective approach to achieve stereoselective cationic polymerization of vinyl ethers. Herein, we provide a deeper understanding of stereoselective ion-pairing polymerization through comprehensive experimental and computational studies. These findings demonstrate the importance of ligand deceleration effects for the identification of reaction conditions that enhance stereoselectivity, which was supported by computational studies that identified the solution-state catalyst structure. An evaluation of monomer substrates with systematic variations in steric parameters and functional group identities established key structure-reactivity relationships for stereoselective homo- and copolymerization. Expansion of the monomer scope to include enantioenriched vinyl ethers enabled the preparation of an isotactic poly(vinyl ether) with the highest stereoselectivity (95.1% ± 0.1 meso diads) reported to date, which occurred when monomer and catalyst stereochemistry were fully matched under a triple diastereocontrol model. The more complete understanding of stereoselective cationic polymerization reported herein offers a foundation for the design of improved catalytic systems and for the translation of isotactic poly(vinyl ether)s to applied areas.