Polar Monomers Research Articles

Exploring the Relationship between the Polyethylene Microstructure and Spatial Structure of α-Diimine Pd(II) Catalysts via a Hybrid Steric Strategy.

The branching density of polyethylene generated in the α-diimine Pd(II) system is usually very high, largely independent of simple ligand modifications with steric or electronic perturbations, or the polymerization conditions. In this study, we designed and synthesized a class of bulky hybrid α-diimine Pd(II) catalysts combining ortho-diarylmethyl and ortho-phenyl moieties to explore the relationship between the polyethylene microstructure and the spatial structure of catalysts. In ethylene polymerization, the hybrid α-diimine Pd(II) catalysts exhibited high activities (well above 105 g·mol-1·h-1) and yielded highly branched (90-110/1000C) polyethylenes with high molecular weights (up to 278.3 kg/mol). Compared with the two corresponding symmetrical ortho-diarylmethyl-based or ortho-phenyl-based Pd(II) catalysts, the hybrid catalysts generated polyethylene of significantly higher branching densities (92 vs 28-34/1000C) in marked higher activities. Similar phenomena are also observed in the copolymerization of ethylene with polar monomers. Moreover, the hybrid Pd(II) catalysts can more efficiently promote the copolymerization of ethylene with various polar monomers in comparison to the corresponding symmetrical catalysts. The more open spatial environment around the metal center by using a hybrid steric strategy was proposed to be responsible for above advantages.

Fluorine Effect on α-Imino-ketone- and Phenoxyiminato Nickel-Catalyzed Ethylene Homo- and Copolymerization

The synthesis of ultrahigh molecular weight polyethylene (UHMWPE) using late transition metal catalysts is highly challenging. In this work, 3,5-bis(trifluoromethyl)phenyl and m-xylyl groups were selected to introduce at the ortho position of 4-(trifluoromethyl)aniline and 4-methylaniline. These amines were condensed with 2,3-butandione and 3-substituted salicylaldehyde and subsequently with nickel precursors to afford cationic keto-imine-based Ni1 and Ni2, as well as 3-substituted neutral phenoxyiminato Ni3 and Ni4 catalysts. The properties of these nickel complexes in ethylene polymerization and copolymerization were studied in detail. Ni2 with a keto-imine framework was found to be highly active in ethylene polymerization with an activity of up to 6.9 × 106 g·mol–1·h–1, whereas the fluorinated Ni1 generated UHMWPE with Mn of up to 2.79 × 106 g·mol–1, along with very low branch density and high Tm values. These nickel catalysts also showed good activity and incorporation of long-chain special polar monomers. It is believed that the higher steric hindrance of fluorine atoms around the metal center may involve suppressing the chain transfer process.

Phosphinobenzenamine Nickel Catalyzed Efficient Copolymerization of Methyl Acrylate with Ethylene and Norbornene

A series of phosphinobenzenamine-based nickel complexes bearing substituted phenylphosphine ligands were synthesized and characterized. These nickel complexes combined with methylaluminoxane (MAO) exhibited very high activity (∼106 g mol–1 h–1) and good thermal stability for norbornene polymerization. The nickel catalysts were able to conduct copolymerization of norbornene and methyl acrylate (MA) with high activity (3.76 × 105 g mol–1 h–1) to give high-molecular-weight functionalized cyclic olefin copolymer (COC) with reasonable MA incorporation (2.39–6.47 mol %). Moreover, the nickel catalysts also promote the copolymerization of ethylene and MA with moderate activity (∼104 g mol–1 h–1) to produce semicrystalline high-molecular-weight polar functionalized polyethylene (PE). The MA incorporation in the copolymer was controlled in a wide range (up to 15.5 mol %). These complexes without any sterically bulky substituent on the ligand are distinctive examples of earth-abundant nickel complexes toward the direct copolymerization of ethylene or norbornene with the challenging vinyl polar monomer MA.

Free radical solution copolymerization of monomers of dissimilar reactivity - influencing chemical composition distribution and properties of copolymers of methyl methacrylate and N-vinyl imidazole by varying monomer feeding profiles

Copolymerization is one way of influencing the properties of polymers and the outcome of copolymerization between vinyl monomers is dependent on the reactivity ratios between the monomers. Incorporation of polar monomers into copolymers offer many benefits. In this regard, N-Vinyl imidazole (NVI) carries much significance as a comonomer. NVI is a specialty monomer. The high polarity and planarity of NVI can impart many beneficial characteristics upon copolymerization with other vinyl monomers. However, its unfavourable reactivity ratios with other vinyl monomers prevent the facile incorporation of NVI in the copolymers. In this work, a semi-continuous solution polymerization is employed with the help of software called Monomer Addition Profile (MAP) to predict the optimal addition profile of the more reactive monomer (methyl methacrylate) through an iterative approach in order to achieve uniform incorporation of less reactive comonomer in the copolymer chain. The predicted chemical composition distribution (CCD) of the copolymerization is used to determine the homogeneity of copolymers which is well supported by the glass transition temperature (Tg) of copolymers. Apart from the workflow of MAP, solubility characteristics of copolymers, microstructure and sequence length are also discussed in this article.

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.

Material Properties of Functional Polyethylenes from Transition-Metal-Catalyzed Ethylene–Polar Monomer Copolymerization

Material Properties of Functional Polyethylenes from Transition-Metal-Catalyzed Ethylene–Polar Monomer Copolymerization

Mitigating Early Phase Separation of Aliphatic Random Ionomers by the Hydrophobic H-Bond Acceptor Addition

This study reports a new phenomenon whereby the ionic content of a random ionomer was increased by the introduction of a hydrophobic modifier. In the current study, the ionomer synthesized from the solution polymerization of the three vinyl monomers, which are polar hydrophobic monomers acrylonitrile (AN), glycidyl methacrylate (GMA), and ionic monomer potassium 3-sulfopropyl methacrylate (SPM), encountered an early phase separation problem when the ionic content exceeded a certain threshold value. However, the addition of a strongly hydrophobic monomer, 2,2,3,3-tetrafluoropropyl methacrylate (TFPM), during the copolymerization is able to restrain this phase separation trend, consequently allowing 50% more of SPM units to be incorporated and uniformly distributed in the ionomer and achieving a random copolymer chain. The ionic clustering of the SPM units, which is the cause for the phase separation, was reduced as a result. The resulting random ionomer was demonstrated to be a superior proton conducting material over its ternary originator. This is due to the fact that TFPM possesses acidic protons, which brings about an association of TFPM with SPM and GMA via hydrogen bonding. This study could impact the synthesis of random ionomers by free radical polymerization since monitoring ionic content and improving ionic unit distribution in ionomers are issues encountered in several industries (e.g., the healthcare industry).

Multivariate Linear Regression Models to Predict Monomer Poisoning Effect in Ethylene/Polar Monomer Copolymerization Catalyzed by Late Transition Metals

This study combined density functional theory (DFT) calculations and multivariate linear regression (MLR) to analyze the monomer poisoning effect in ethylene/polar monomer copolymerization catalyzed by the Brookhart-type catalysts. The calculation results showed that the poisoning effect of polar monomers with relatively electron-deficient functional groups is weaker, such as ethers, and halogens. On the contrary, polar monomers with electron-rich functional groups (carbonyl, carboxyl, and acyl groups) exert a stronger poisoning effect. In addition, three descriptors that significantly affect the poisoning effect have been proposed on the basis of the multiple linear regression model, viz., the chemical shift of the vinyl carbon atom and heteroatom of polar monomer as well as the metal-X distance in the σ-coordination structure. It is expected that these models could guide the development of efficient catalytic copolymerization system in this field.

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.

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.

An Ionic Cluster Strategy for Performance Improvements and Product Morphology Control in Metal-Catalyzed Olefin-Polar Monomer Copolymerization.

Product morphology control represents a critical challenge for polyolefin production, but it has remained largely unexplored in the field of ethylene-polar monomer copolymerization. Herein, an ionic cluster strategy was designed to control the product morphology during the synthesis of polar-functionalized polyolefins via precipitation polymerization. In addition to product morphology control, simultaneous improvements in the catalytic copolymerization performance (activities, copolymer molecular weights, and comonomer incorporation ratios) were achieved. These results were due to less poisoning of the metal-salt-based comonomers compared with their ester counterparts and the high local concentration of the alkene comonomers induced by ionic cluster formation. Moreover, the ionic cluster strategy is generally applicable to various comonomers and catalytic systems, greatly enhances the catalyst's thermal stability at high temperatures (90-150 °C), and enables the homopolymerization of both terminal and internal polar-functionalized olefins. Finally, polar-functionalized polyolefins and polyolefin composites (generated from a tandem process combining a prepolymerization step and subsequent polymerization) were developed, which showed tunable mechanical properties and great potential as compatibilizing agents for mixtures of polyolefins and other types of polymers.

Reactivity of Phosphino‐naphtholate Nickel Complexes and Their Catalysis of Copolymerization with Polar Monomers

AbstractCoordination‐insertion copolymerization of ethylene with polar monomers can directly provide value‐added functionalized polyolefins. Studies on the reactivity of catalysts toward polar monomers can help understand the copolymerization process and then tune the polymerization strategically. In this contribution, the reactivity picture of 2‐diphenylphosphonyl‐8‐phenylnaphthol nickel complex toward fundamental polar monomers was explored by stoichiometric reactions. The insertion rates are in the order of methyl acrylate (MA)>n‐butyl acrylate (BA)>N, N‐dimethylacrylamide (DMAA)>methyl methacrylate (MMA)>vinyl triethoxysilane (VTEoS)>N‐vinyl‐pyrrolidinone (NVP). Acrylic derivatives of MA, BA and DMAA with electron‐withdrawing group favor 2,1‐fashion while non‐acrylic NVP with electron‐donating group prefers 1,2‐fashion. Notably, the 1,1‐disubstituted MMA and bulky VTEoS perform a preferential 1,2‐insertion accompanying by 2,1‐insertion in the percentage of 82 : 18 and 62 : 38, respectively, because of the stronger steric effect. These insights correlate to the copolymerization of polar monomers with ethylene. Linear functional polyethylene with in‐chain and terminal incorporation of BA, DMAA or VTEoS is afforded at a high activity.

Enhancement on Hemilabile Phosphine-Amide Palladium and Nickel Catalysts for Ethylene (Co)Polymerization with Polar Monomers Using a Cyclizing Strategy

Enhancement on Hemilabile Phosphine-Amide Palladium and Nickel Catalysts for Ethylene (Co)Polymerization with Polar Monomers Using a Cyclizing Strategy

Isospecific (Co)polymerization of Unmasked Polar Styrenes by Neutral Rare-Earth Metal Catalysts.

Syndioselective polymerization of unprotected polar styrenes has achieved great success via specially designed catalysts and the establishment of "self-assisted" theory. In contrast, isospecific polymerization of polar styrenes has remained less explored. Herein, we present new racemic ansa-bis(benz[e]indenyl) rare-earth metal complexes and their high activity and perfect isoselectivity (mmmm>99 %) for the polymerization of unmasked polar styrenes without any activators. Moreover, the copolymerizations of para- and meta-methoxystyrenes with styrene give gradient and random copolymers, respectively. The insertion rate of polar monomers could be readily tuned in the range of 0-100 mol % by changing their loading ratios. The resultant isotactic polar polystyrenes are quantitatively transformed into hydroxyl or methylsulfonyl polystyrenes with high Tg s. DFT calculations reveal the isospecific mechanism.

Isospecific (Co)polymerization of Unmasked Polar Styrenes by Neutral Rare‐Earth Metal Catalysts

AbstractSyndioselective polymerization of unprotected polar styrenes has achieved great success via specially designed catalysts and the establishment of “self‐assisted” theory. In contrast, isospecific polymerization of polar styrenes has remained less explored. Herein, we present new racemic ansa‐bis(benz[e]indenyl) rare‐earth metal complexes and their high activity and perfect isoselectivity (mmmm>99 %) for the polymerization of unmasked polar styrenes without any activators. Moreover, the copolymerizations of para‐ and meta‐methoxystyrenes with styrene give gradient and random copolymers, respectively. The insertion rate of polar monomers could be readily tuned in the range of 0–100 mol % by changing their loading ratios. The resultant isotactic polar polystyrenes are quantitatively transformed into hydroxyl or methylsulfonyl polystyrenes with high Tgs. DFT calculations reveal the isospecific mechanism.

Fouling Prevention in Polymeric Membranes by Radiation Induced Graft Copolymerization.

The application of membrane processes in various fields has now undergone accelerated developments, despite the presence of some hurdles impacting the process efficiency. Fouling is arguably the main hindrance for a wider implementation of polymeric membranes, particularly in pressure-driven membrane processes, causing higher costs of energy, operation, and maintenance. Radiation induced graft copolymerization (RIGC) is a powerful versatile technique for covalently imparting selected chemical functionalities to membranes’ surfaces, providing a potential solution to fouling problems. This article aims to systematically review the progress in modifications of polymeric membranes by RIGC of polar monomers onto membranes using various low- and high-energy radiation sources (UV, plasma, γ-rays, and electron beam) for fouling prevention. The feasibility of the modification method with respect to physico-chemical and antifouling properties of the membrane is discussed. Furthermore, the major challenges to the modified membranes in terms of sustainability are outlined and the future research directions are also highlighted. It is expected that this review would attract the attention of membrane developers, users, researchers, and scientists to appreciate the merits of using RIGC for modifying polymeric membranes to mitigate the fouling issue, increase membrane lifespan, and enhance the membrane system efficiency.

Relative effects of polymer composition and sample preparation on glass dynamics

Modern design of common adhesives, composites and polymeric parts makes use of polymer glasses that are stiff enough to maintain their shape under a high stress while still having a ductile behavior after the yield point. Typically, material compositions are tuned with co-monomers, polymer blends, plasticizers, or other additives to arrive at a tradeoff between the elastic modulus and toughness. In contrast, strong changes to the mechanics of a glass are possible by changing only the molecular packing during vitrification or even deep in the glassy state. For example, physical aging or processing techniques such as physical vapor deposition increase the density, embrittle the material, and increase elastic modulus. Here, we use molecular simulations, validated by positron annihilation lifetime spectroscopy (PALS) and quasi-elastic neutron scattering, to understand the free volume distribution and the resulting dynamics of glassy co-polymers where the composition is systemically varied between polar 5-norbornene-2-methanol (NBOH) and non-polar ethylidene norbornene (ENB) monomers. In these polymer glasses, we analyze the structural features of the unoccupied volume using clustering analysis, where the clustering is parameterized to reproduce experimental measurements of the same features from PALS. Further, we analyze the dynamics, quantified by the Debye-Waller factor, and compare the results with softer, lower density states. Our findings indicate that faster structural relaxations and potentially improved ductility are possible through changes to the geometric structure and fraction of the free volume, and that the resulting changes to the glass dynamics are comparable to large changes in the monomer composition.

Design and synthesis of binuclear vanadium catalysts for copolymerization of ethylene and polar monomers

Binuclear vanadium complexes exhibited higher activity than monometallic complexes in ethylene polymerization and afforded UHMWPE. The binuclear catalysts also showed moderate activity in copolymerization with 10-undecen-1-ol and methyl 10-undecenoate.

Sterically rigid bismuth pincer complexes; observation of the growing polymer chain in polar monomer polymerisation.

A family of pyridine dipyrrolide bismuth complexes (Mes,PhL)MX (1-6) (M = Bi, X = O-2,6-Me-C6H3 = OXyl (1); M = Sb, X = OXyl (2); M = Bi, X = O-2,6-iPr-C6H3 = ODipp (3), O-2,6-tBu-C6H3 = OArtBu (4), OtBu (5) and OCMe2Et = OAm (6), N(SiMe3)2 = N'' (7) and CH2Ph (8)) have been prepared and investigated as initiators for the ring-opening polymerisation of lactide monomers. Bismuth lactate complexes (Mes,PhL)Bi{OC(H)(Me)C(O)OR} were prepared as models for the propagating species (R = tBu (9), Me (10), iPr (11)). The first insertion of the lactide monomer is rate limiting and the second and subsequent insertions are more rapid (kinit ≪ kLA2 < kprop), leading to a significant induction period. The sterically demanding, rigid pincer ligand affords a well-defined coordination environment at the metal centre and allows for the enchainment of two lactide monomers to be differentiated spectroscopically ((Mes,PhL)Bi{OC(H)(Me)C(O)}4OX (12-X)), with this species also implied to be the true initiator for the regime of propagation with first order kinetics. Well-controlled first order kinetic data for the polymerisation of L-, D-, rac- and meso-lactide are observed.

Polar additive triggered chain walking copolymerization of ethylene and fundamental polar monomers

The use of a polar additive efficiently triggers chain walking copolymerization of ethylene with a broad scope of fundamental polar monomers, which is long-sought in an α-diimine Pd(ii) system.