Formation Of Block Copolymers Research Articles

Switchable Copolymerization of Maleic Anhydride/Epoxides/Lactide Mixtures: A Straightforward Approach to Block Copolymers with Unsaturated Polyester Sequences

AbstractSwitchable copolymerization of oxygenated heterocycle mixtures by a single catalytic system has been proved to be a promising approach to sequence‐controlled block copolymers. However, there are still big challenges in one‐step synthesis of multiblock copolymers containing unsaturated polyester blocks from maleic anhydride, epoxides, and lactone mixtures. Herein, a switchable pathway for polylactide‐b‐poly(MAH‐alt‐epoxide)‐b‐polylactide block copolymers is established. The excellent chemoselectivity in multicomponent copolymerization is achieved by bipyridine bisphenolate aluminum complexes that can induce an obvious kinetic differentiation between ring‐opening copolymerization of maleic anhydride/epoxides and ring‐opening polymerization of lactide. The scope of the epoxide for switchable copolymerization is explored and it is found that the steric hindrance of the substituents on epoxide significantly influences the formation of block copolymers. Block copolymers with various sequential and topological structures can be easily prepared by exquisite selection of different initiators. Furthermore, it is demonstrated that the conversion of cis‐maleate units in the block copolyester could be completely converted to trans‐fumarate units by isomerization without chain degradation, cross‐linking, and chain scrambling.

Separated Micelles Formation of pH-Responsive Random and Block Copolymers Containing Phosphorylcholine Groups.

The self-assembly of pH-responsive random and block copolymers composed of 2-(N,N-diisopropylamino)ethyl methacrylate and 2-methacryloyloxyethyl phosphorylcholine was investigated in aqueous media. Their pH-responsive behaviors were investigated in aqueous media by dynamic light scattering (DLS) and fluorescence measurements using a pyrene hydrophobic fluorescence probe. In an acidic environment, these copolymers existed as single polymer chains that did not interact with each other. In contrast, upon increasing the pH of the solution above the critical value of ~8, separated micelles were formed in the mixture, which was indicated by bimodal distribution in DLS results with radius of 4.5 and 10.4 nm, corresponding to the random and block copolymer micelles, respectively. Fluorescence resonance energy transfer efficiencies were near to zero in the mixture of the donor labeled block and acceptor labeled random copolymers under both acidic and basic pH. These results demonstrated the coexistence of two distinct micelles.

INFLUENCE OF ADDITIONAL INHIBITORS ON CATALYTIC DESTRUCTION REACTION OF POLYISOBUTYLENE

It is impossible to create a scientific basis for the synthesis of polymers without taking into account the destruction process. Under the action of Lewis acids, the destruction of PIB follows a free radical chain mechanism, while the catalytic destruction of PIB leads to the formation of both linear and branched macromolecules. The most wide-spread type of chemical destruction is an oxidative destruction by oxygen and ozone. The oxidative destruction is activated by heat, light rays and mechanical energy, and the types of thermal, photo and mechanical oxidative destruction are known, respectively. As a result of these destructive reactions, both the composition and the structure of polymer change, that is, it “grows old”. The aging of a polymer means a change in its physical-chemical, physical-mechanical properties during exploitation . The fastest oxidative destruction of polymers occurs by a chain mechanism (with free radicals), as in low molecular weight hydrocarbons. The oxidation process of polymers without double bonds in the chains proceeds weakly, and the formation of peroxide groups is not always observed in them. This process consists of three stages: formation of an active center, lengthening and breaking of the chain. It is known that oxidation begins with the formation of peroxides. Active centers are obtained by the decomposition of peroxides. When studying the chemistry of the reaction, it was noticed that there is another mechanism for the destruction of polyisobutylene in the presence of strong Lewis acids, characteristic of cationic processes. One of the interesting aspects of the destruction process is a complete understanding of the "chemistry" of catalytic destruction. For this, various additives must be added to the catalytic reaction. During the experiments it has been found that the reaction does not take place in a completely dried solvent. The reaction proceeds when a significant amount of water is added to the system. The amount of water in the system is [H2O] ≈10-3 mol / l. This can be explained by the fact that the catalyst in dimer form is inactive in the nonpolar helix, but the water plays the role of a polar additive, decomposing the dimer catalyst and converting it into the monomeric form of Brønsted acid. Therefore, the inhibitory effect of 2,6-DTBP and toluene on the reaction has been studied in order to fully elucidate the chemistry of the catalytic destruction of PIB by Lewis acids. Since 2,6-DTBP is a trap for protons, it plays an important role in the detection of the active form of the catalyst. The ineffectiveness of 2,6-DTBP and toluene as an inhibitor led to the existence of a radical reaction mechanism and the discovery of the active form of the catalyst. For better understanding the reaction mechanism, the inhibitory effect of O2, p-benzoquinone and tetracyanethylene on the reverse process has been studied. The formation of block copolymers upon modification of PIB with acrylonitrile and vinyl acetate, polymerized by the radical mechanism, not only confirms the radical mechanism of destruction, but also creates conditions for the production of new copolymers. The formation of active centers has been also confirmed by the EPR method, free macroradicals have been detected and their density has been determined. The formation of free macroradicals as a result of the direct action of strong mechanical energy, direct mechanical cracking or transfer of vibration energy of the initial highly active state of the polymer chain is the initial stage of mechanical and chemical processes. The overall final result of the transformations depends on the direction of the subsequent secondary reactions of free macroradicals. Although these reactions are different, they correspond to typical free radical processes in polymer systems. On the whole, destructive reactions are considered one of the most important reactions for high molecular weight compounds. They are used to study the structure of high molecular weight compounds, as well as to obtain low molecular weight compounds from the natural polymers. All this has been reflected in IR, UV, NMR, EPR spectroscopic studies. A mathematical and kinetic model of the processes has been developed and parameters have been calculated using the experimental indicators of the carried out researches. Keywords: catalyst, 2,6-DTBP, toluene, polyisobutylene, destruction, halide, aikyl halide, inhibitor, deactivation, methano

Ambient Temperature Polymerization of Methyl Methacrylate Mediated by Ate Complexes

AbstractFinding catalysts that are both robust and highly active at room temperature can often be considered as a daunting challenge. Yet, these features are desirable for polymer synthesis as they allow to produce materials of interest easily and sustainably. Herein, commercial reagents are used to form in situ “ate” complexes which were found to be highly active in the room temperature anionic polymerization of methyl methacrylate. Also of particular interest is their ability to polymerize rac‐lactide, and even form block copolymers of poly(methyl methacrylate) and poly(lactic acid).

Facile one-step fabrication of DMAP-functionalized catalytic nanoreactors by polymerization-induced self-assembly in water

Fabrication of highly efficient and recyclable micellar nanoreactors for green organic transformation via self-assembly of catalyst-containing amphiphilic copolymers in water has made great progress. These methods commonly include synthesis and functionalized amphiphilic copolymers and then self-assembly. In this study, a straightforward, one-step strategy for the construction of DMAP-functionalized nanoreactors was developed via polymerization-induced self-assembly (PISA). Acrylate hydrophilic monomer and DMAP-functionalized monomer in the presence of hydrophilic macromolecular chain transfer reagent was polymerized through reversible addition-fragmentation chain transfer (RAFT) polymerization in situ in water, leading to simultaneous amphiphilic block copolymer formation and self-assembly. The diameters of the resulted micelles ranged from 20 to 100 nm depending on the type and amount of hydrophilic monomer, and solid content is up to 25%. The high catalytic activity of the micelles as homogeneous, also readily recyclable catalysts is demonstrated through acylation of a variety of alcohols and recovery by simple dialysis. The study offers an one-pot tandem RAFT-PISA process in water for fabricating highly efficient catalytic nanoreactor.

Block Copolymers Based on Ethylene and Methacrylates Using a Combination of Catalytic Chain Transfer Polymerisation (CCTP) and Radical Polymerisation.

Two scalable polymerisation methods are used in combination for the synthesis of ethylene and methacrylate block copolymers. ω‐Unsaturated methacrylic oligomers (MMAn) produced by catalytic chain transfer (co)polymerisation (CCTP) of methyl methacrylate (MMA) and methacrylic acid (MAA) are used as reagents in the radical polymerisation of ethylene (E) in dimethyl carbonate solvent under relatively mild conditions (80 bar, 70 °C). Kinetic measurements and analyses of the produced copolymers by size exclusion chromatography (SEC) and a combination of nuclear magnetic resonance (NMR) techniques indicate that MMAn is involved in a degradative chain transfer process resulting in the formation of (MMA)n‐b‐PE block copolymers. Molecular modelling performed by DFT supports the overall reactivity scheme and observed selectivities. The effect of MMAn molar mass and composition is also studied. The block copolymers were characterised by differential scanning calorimetry (DSC) and their bulk behaviour studied by SAXS/WAXS analysis.

Synthesis and characterization of benzodioxinone mono-telechelics and their use in block copolymerization.

Poly(methyl methacrylate) (PMMA) and poly(ethylene glycol) methyl ether (mPEG)-based monotelechelics were quantitatively prepared by copper (I)-catalyzed azide/alkyne cycloaddition (CuAAC) click reactions using azido-terminated polymers and alkyne functional benzodioxinones. The monotelechelic containing dimethyl moities (2,2-dimethyl-5-(prop-2-yn-1-yloxy)-4H-benzo[d][1,3]dioxin-4-one) was heat-sensitive, whereas the monotelechelic containing diphenyl moieties (2,2-diphenyl-5-(prop-2-yn-1-yloxy)-4H-benzo[d][1,3]dioxin-4-one) was UV light sensitive. Based on the FT-IR, 1H-NMR, and GPC investigations, the CuAAC click reactions enable the quantitative syntheses of monotelechelics under mild conditions. Moreover, the photosensitive mPEG-based monotelechelic was further utilized for the block copolymer synthesis upon UV-light irradiation. The photoinduced acylation of mPEG monotelechelic consist of (2,2-diphenyl-5-(prop-2-yn-1-yloxy)-4H-benzo[d][1,3]dioxin-4-one) in the presence of hydroxy-terminated poly(epsilon caprolactone) enabled the successful block copolymer formation.

Aldehyde-Functionalized Polymers from the Reverse Iodine Transfer Polymerization of Lignin-Derivable Compounds

Renewable polymers with reactive functionalities become increasingly attractive as they address some critical global concerns related to sustainability. In this work, vanillin methacrylate (VM), an aldehyde-functionalized monomer synthesized by the methacrylation of vanillin (a possible lignin derivative), was polymerized for the first time via reverse iodine transfer polymerization. The influence of various reaction parameters including the polymerization solvent, the initiator-to-iodine ratio, and the polymerization temperature on the induction (or inhibition) period and the molar mass was investigated by 1H NMR spectroscopy and size exclusion chromatography. The lack of a clear and consistent discoloration of the reaction mixture to indicate the end of the induction period in the solvents investigated, i.e., toluene, methyl ethyl ketone (MEK), and N,N-dimethylformamide (DMF), was an indication that iodine was taking part in a side (complexation) reaction with the solvent. When the monomer conversions were followed by 1H NMR spectroscopy, it was found that the induction periods for the reactions carried out in MEK and DMF were significantly shorter due to the consumption of iodine by VM, leading to the formation of a chain transfer agent (CTA), 4-formyl-2-methoxyphenyl-2-iodo-2-methylpropanoate. The formation of polymer chains derived from this CTA was confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. To demonstrate the “livingness” of the polymerization process, PVM was chain-extended with methyl methacrylate, and the formation of block copolymers was confirmed by high-performance liquid chromatography. The application toolbox of these polymers was expanded by the formation of various poly(vanillin methacrylate) Schiff base polymers endowed with additional functional groups.

How the Reactive End Group of Macro-RAFT Agent Affects RAFT-Mediated Emulsion Polymerization-Induced Self-Assembly.

Polymerization-induced self-assembly via reversible addition-fragmentation chain transfer (RAFT)-mediated emulsion polymerization is an emerging method in which macro-RAFT agents are chain extended with hydrophobic monomers in water to form block copolymer nano-objects. However, almost all RAFT-mediated emulsion polymerizations are limited to AB diblock copolymers by using monofunctional macro-RAFT agents with non-reactive end groups. In this study, the first investigation on how the reactive end group of macro-RAFT agent affects RAFT-mediated emulsion polymerization is reported. Three macro-RAFT agents with different end groups are synthesized and employed in RAFT-mediated emulsion polymerization. Effects of end groups on morphologies of block copolymer nano-objects and polymerization process are studied. Block copolymer nano-objects prepared by using an asymmetric difunctional macro-RAFT agent can be functionalized by further chain extension on the surface. It is expected that the current study will not only expand the scope of RAFT-mediated emulsion polymerization, but also provide a novel strategy to prepare functional polymer nanoparticles.

Allylthioketone mediating radical polymerization of butyl acrylate

By combination of high trapping radical efficiency of thioketone with resonance of allylic radicals, a novel mediated agent, 1, 3, 3-triphenylprop-2-ene-1-thione (TPPT) has been successfully synthesized. 1H NMR method was used to trace the TPPT-mediated radical polymerization of butyl acrylate (BA) at 50 °C, we observed that the disappearance rates of BA, TPPT and initiator, dimethyl 2,2′-azobis (2-methylpropionate) (AIBME) have the following order: BA > AIBME > TPPT, monomer conversion increases gradually with proceeding of the polymerization and approximately 84% of conversion was obtained within 24 h of the polymerization. The molecular weights of the obtained PBA are not varied obviously with the conversion, but the molecular weight distributions are narrow. The matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) studies reveal three polymerization mechanisms. The TPPT can efficiently capture the growing PBA radicals to form PBA-TPPT• radicals, and this highly stable radicals are able to be cross-terminated by the growing PBA• radicals or primary radicals to form the dormant chains. Although the reversed reaction of reaction 1 is very slow, the extension polymerization of the PBA can undergo to form block copolymers. The molecular weight of the formed PBA is influenced by the feed molar ratio of BA/TPPT and TPPT/AIBME.

Synthesis of poly (n-butyl acrylate) with tempo by nitroxide mediated polymerization method

It has been observed that acrylate monomers are very difficult to polymerize with the low cost nitroxide catalyst 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO). Therefore, costly acyclic nitroxides such as N-tert-butyl-N-(1-diethylphosphono-2,2-dimethyl)-N-oxyl, (SG1), 2,2,5-Trimethyl-4-phenyl-3-azahexane-3-nitroxide (TIPNO) and TIPNO derivatives have to be used for the polymerization of the acrylic acid derivatives. There are very few reports on the use of TEMPO-derivatives toward the polymerization of n-butyl acrylate. Generally different reducing agents viz. glucose, ascorbic acid, hydroxyacetone etc. have been used to destroy excess TEMPO during the polymerization reaction. The acrylate polymerizations fail in the presence of TEMPO due to the strong C–O bond formed between the acrylate chain end and nitroxide. To the best of our knowledge, no literature report is available on the use of TEMPO without reducing agent or high temperature initiators, toward the polymerization of n-butyl acrylate. The present study has been carried out with a view to re-examine the application of low cost nitroxide TEMPO, so that it can be utilized towards the polymerization of acrylate monomers (e.g. n-butyl acrylate). We have been able to polymerize n-butyl acrylate using the nitroxide TEMPO as initiator (via a macroinitiator). In this synthesis, a polystyrene macroinitiator was synthesized in the first step from TEMPO, after this TEMPO end-capped styrene macroinitiator (PSt-TEMPO) is used to polymerize n-butyl acrylate monomer. The amount of macroinitiator taken was varied from 0.05% to 50% by weight of n-butyl acrylate monomer. The polymerization was carried out at 120°C by bulk polymerization method. The experimental findings showed a gradual increase in molecular weight of the polymer formed and decrease in the polydispersity index (PDI) with increase in amount of PSt-TEMPO macroinitiator taken. In all experiments conversion was more than 80%. These results indicate that the polymerization takes place through controlled polymerization process. Effect of different solvents on polymerization has also been investigated. In the following experiments TEMPO capped styrene has been used as macroinitiator leading to the successful synthesis of poly n-Butyl acrylate. It has been found that styrene macroinitiator is highly efficient for the nitroxide mediated polymerization, even in very small concentration for the synthesis of poly n-butyl acrylate. High concentration of macroinitiator results in the formation of block copolymers of polystyrene and poly ( n-butyl acrylate) viz. polystyrene-block-poly-( n-butyl acrylate). The use of TEMPO toward controlled polymerization is of much importance, because it is the nitroxide commercially available at the lowest cost.

Light-controlled, living radical polymerisation mediated by fluorophore-conjugated RAFT agents

Photoinduced electron transfer-reversible addition−fragmentation chain-transfer (PET-RAFT) polymerisation allows the controlled synthesis of polymers and provides an alternative to transition metal-based photoinitiators. Here, fluorophore-conjugated RAFT agents, containing either 5-carboxyfluorescein or a “boron-dipyrromethene” (BODIPY) moiety attached to a thiocarbonylthio group, were synthesised. Both agents enabled light-controlled (470 nm, 0.4 mW/cm2) “on/off” polymerisation yielding polymers with a Mw/Mn < 1.50. The BODIPY-based RAFT agent showed excellent photostability and gave polymers that contained a single fluorophore per polymer chain, providing an expedient route to homogeneous fluorescently labelled polymers. This agent was compatible with multiple acrylamide/acrylate monomers with a range of functional groups, with the thiocarbonylthio terminating group enabling further polymer chain extension and the formation of fluorescent block copolymers, as demonstrated by the synthesis of BODIPY-labelled poly(N,N-dimethylacrylamide)-block-poly (3-acrylamidophenyl)boronic acid).

Visible Light Induced Step-Growth Polymerization by Substitution Reactions.

A new visible light induced step-growth polymerization of dibromoxylene, and diols using dimanganese decacarbonyl and diphenyliodonium salt is described. The polymerization is suggested to proceed by substitution reaction between dixylenium cations formed upon visible light irradiation in the presence of dimanganese decacarbonyl and diphenyl iodonium salt. For the described substitution reaction with diols as nucleophilic component, the scope of the process is studied. Furthermore, the presence of halide groups at chain ends of the resulting polymers provided the possibility of initiating subsequent free radical and free radical promoted cationic resulting in the formation of polyether-based block copolymers.

Probing Thermoresponsive Polymerization-Induced Self-Assembly with Variable-Temperature Liquid-Cell Transmission Electron Microscopy

Summary We directly initiate and visualize the formation of polymeric nanomaterials via variable-temperature liquid-cell transmission electron microscopy (VT-LCTEM). With temperature control in the liquid cell, reversible addition-fragmentation chain transfer polymerization was thermally initiated, leading to the formation of amphiphilic block copolymers that assemble upon dispersion polymerization-induced self-assembly (PISA). In combination with traditional ex situ analyses, VT-LCTEM enabled not only the characterization of the nanoparticles in situ but also the observation of a thermal phase transition. Critically, because these assemblies form from thermoresponsive components, any temperature changes during sample preparation and analysis can alter morphologies, necessitating direct in situ characterization of reaction progression. We believe that the findings and the technique described herein will lead to unprecedented possibilities for the development and characterization of self-organizing soft matter.

Selenonium Polyelectrolyte Synthesis through Post-Polymerization Modifications of Poly (Glycidyl Methacrylate) Scaffolds.

Atom transfer radical polymerization of glycidyl methacrylate monomer with poly(ethylene glycol)-based macroinitiators leads to the formation of reactive block copolymers. The epoxide side-chains of these polymers can be subjected to a regiospecific base-catalyzed nucleophilic ring-opening reaction with benzeneselenol under ambient conditions. The ß-hydroxy selenide linkages thus formed can be alkylated to access polyselenonium salts. 77Se-NMR indicates the formation of diastereomers upon alkylation. In such a manner, sequential post-polymerization modifications of poly(glycidyl methacrylate) scaffolds via selenium-epoxy and selenoether alkylation reactions furnish practical access to poly(ethylene glycol)-based cationic organoselenium copolymers.

Consequences of Molecular Architecture on the Supramolecular Assembly of Discrete Block Co-oligomers.

Supramolecular block copolymers composed of discrete blocks have promising properties for nanotechnology resulting from their ability to combine well-defined morphologies with good bulk material properties. Here, we present the impact of a well-defined siloxane block in either the main-chain or present as pendant grafts on the properties of supramolecular block copolymers that form ordered nanostructures with sub-5 nm domains. For this, two types of supramolecular block copolymers were synthesized based on the ureidopyrimidinone–urethane (UPy-UT) motif. In the first, oligodimethylsiloxanes (oDMS) of discrete length were end-capped with the UPy-UT motif, affording main-chain UPy-UT-Sin. In the second, the UPy-UT motif was grafted with discrete oDMS affording grafted UPy-UT-g-Si7. For the two systems, the compositions are similar; only the molecular architecture differs. In both cases, crystallization of the UPy-UT block is in synergy with phase segregation of the oDMS, resulting in the formation of lamellar morphologies. The grafted UPy-UT-g-Si7 can form long-range ordered lamellae, resulting in the formation of micrometer-sized 2D sheets of supramolecular polymers which show brittle properties. In contrast, UPy-UT-Sin forms a ductile material. As the compositions of both BCOs are similar, the differences in morphology and mechanical properties are a direct consequence of the molecular architecture. These results showcase how molecular design of the building block capable of forming block copolymers translates into controlled nanostructures and material properties as a result of the supramolecular nature of the interactions.

EFFECT OF AZOINITIATORS OF METHYL METHACRYLATE POLYMERIZATION ON THE FORMATION PROCESS AND MORFOLOGY OF POLYURETHANE /POLYMETHYL METHACRYLATE INTERPENETRATING POLYMER NETWORKS

Interpenetrating polymer networks (IPN) are mixtures of two cross-linked polymers formed as a result of chemical reactions of in situ synthesis of components from single-phase initial mixtures. As a rule, due to the incompatibility of the components, a physical process of phase separation takes place with the formation of heterogeneous systems with insignificant interphase adhesion, which can have a negative effect on the physicochemical properties. To increase the compatibility of the components and to stabilize the systems, compatibilizers are introduced into the reaction mixtures. In this work the kinetics of the in situ formation of the components of polyurethane/poly(methyl methacrylate) interpenetrating polymer networks and the phase separation induced by chemical reactions in the presence of methyl methacrylate polymerization oligoazoinitiators in the reaction mixture were studied. Oligoazoinitiators contained fragments of a polyurethane chain also. It has been shown that the introduction of oligoazoinitiators of various chemical natures can control the process of IPN formation due to the formation of block copolymers during synthesis, which are compatibilizers of the mixture. They slow down the phase separation process and favor the formation of a finer IPN structure.

Multifactor Control of Vinyl Monomer Sequence, Molecular Weight, and Tacticity via Iterative Radical Additions and Olefin Metathesis Reactions.

Monomer sequence control in terms of a single monomer unit, particularly in vinyl polymers, is one of the largest challenges in polymer chemistry. Furthermore, multifactor control of monomer sequence, molecular weight, and stereoregularity is an ultimate goal. In this work, we propose a strategy to prepare C-C main-chain sequence-regulated polymers with controlled molecular weights from vinyl monomers via a combination of iterative atom transfer radical additions and olefin metathesis reactions. This strategy enabled the synthesis of sequence-regulated polymers with exact styrene-acrylate-styrene sequences in the C-C main chains, controlled molecular weights of up to 104, and stereoregularities varying with syndiotacticity, isotacticity, and heterotacticity. The utility of this strategy is further demonstrated by formation of block copolymers consisting of sequence-regulated vinyl polymer segments by combining living ROMP of norbornene derivatives.

Temperature Variation Enables the Design of Biobased Block Copolymers via One-Step Anionic Copolymerization.

A one-pot approach for the preparation of diblock copolymers consisting of polystyrene and polymyrcene blocks is described via a temperature-induced block copolymer (BCP) formation strategy. A monomer mixture of styrene and myrcene is employed. The unreactive nature of myrcene in a polar solvent (tetrahydrofuran) at -78°C enables the sole formation of active polystyrene macroinitiators, while an increase of the temperature (-38°C to room temperature) leads to poly(styrene-block-myrcene) formation due to polymerization of myrcene. Well-defined BCPs featuring molar masses in the range of 44-117.2kgmol-1 with dispersities, Ð, of 1.09-1.21, and polymyrcene volume fractions of 30-64% are accessible. Matrix assisted laser desorption ionization-time of flight mass spectrometry measurements reveal the temperature-controlled polymyrcene block formation, while both transmission electron microscopy and small-angle X-ray scattering measurements prove the presence of clearly microphase-separated, long range-ordered domains in the block copolymers. The temperature-controlled one-pot anionic block copolymerization approach may be general for other terpene-diene monomers.

Grafting of Lanthanum Complexes on a Functionalized Graphene Surface: Theoretical Investigation on Ethylene and 1,3-Butadiene Homo- and Co-Polymerization.

In this contribution, we describe the use of graphene as an efficient catalyst support and the role it plays in increasing the Lewis acidity of the supported metal complexes. By a density functional theory study, we show that the [La(N(SiMe3 )2 )3 ] complex can be easily grafted on graphene-OH and -COOH functionalized surfaces. Two stable mono-grafted compounds, (gO)-[La(N(SiMe3 )2 )2 ] and (gOO)-[La(N(SiMe3 )2 )2 ], are formed, behaving as stronger Lewis acids than the previously reported silica grafted analogues. To study the role of the graphene support in catalysis, we also computed the catalytic activity of the alkylated (gO)-[La(CH3 )2 ] and (gOO)-[La(CH3 )2 ] complexes in the ethylene and 1,3-butadiene homo- and co-polymerization reactions. Both compounds are efficient catalysts for the homo-polymerization of the ethylene and 1,3-butadiene. For the 1,3-butadiene homo-polymerization, the stereoselectivity outcome of the reaction differs according to the grafting site. The results computed for the co-polymerization reaction, finally, show that the high stability of the allylic products leads to the formation of block copolymers.