Free Radical Polymerization Of Vinyl Monomers Research Articles

(Invited) Lithium Battery Interfacial Engineering with Thin Conformal Polymer Coatings

Coupled chemical and mechanical phenomena at electrode interfaces largely govern the reversibility and long term stability of lithium ion and lithium metal batteries. A well-known example in lithium ion batteries is the formation of the electrically insulating, ionically conductive, continuous solid electrolyte interface (SEI) on graphitic anodes, which passivates the electrode against further electrochemical reduction of the electrolyte. Unfortunately, this stable passivation does not occur in Si and Li metal anodes. High voltage cathodes are also prone to detrimental interfacial processes, resulting in electrolyte oxidation, gas formation, and transition metal dissolution. In response, a myriad of coating technologies has been developed to mitigate and control these interfacial phenomena and enable next-generation electrodes. These technologies must provide thin, conformal coatings over the entire electrochemically active surface area of the electrode; the coatings must also possess the requisite mechanical properties to accommodate volume dilation due to lithium insertion/extraction.This presentation will describe the development of conformal, compliant polymer thin film coatings for lithium battery electrodes. The polymer thin films are prepared by initiated chemical vapor deposition (iCVD), which provides exquisite control over film composition and morphology by facilitating heterogeneous free-radical polymerization of vinyl monomers with thickness precision on the order of 1 nm. Poly(1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane) (pV4D4) was deposited onto silicon thin film electrodes using iCVD. 25 nm-thick pV4D4 films on Si electrodes improved initial coulombic efficiency by 12.9% and capacity retention over 100 cycles by 64.9% relative to untreated electrodes. PV4D4 coatings also improved rate capabilities, enabling higher lithiation capacity at all current densities. Post-cycling FTIR and XPS showed that pV4D4 inhibited electrolyte reduction and altered the SEI composition, with enrichment in LiF. In another example, thin conformal coatings of perfluorinated polymer were deposited onto battery-grade Cu current collectors to function as an artificial solid electrolyte interface. The effect of the film thickness on Li cycling reversibility was characterized. By galvanostatically cycling Li in an asymmetric Li||Cu cell using 1M LiFSI in a 1:1 (v/v) mixture of dioxolane:dimethoxyethane at 30°C, it was shown that the average coulombic efficiency averaged over 50 cycles increased from 98.36% for bare, untreated Cu to 99.08% for Cu coated with 25 nm of the fluoropolymer. Moreover, the 25 nm coating suppressed interfacial impedance growth on the current collector; the resistance of the coated Cu was 40% lower than the untreated Cu after 100 cycles. The mechanism by which the polymer coating enhances coulombic efficiency and suppresses side reactions will be discussed, along with discussion of the performance in practical anode-free lithium metal batteries.

Virtual Free-Radical Polymerization of Vinyl Monomers in View of Digital Twins.

The first case of virtual polymerization based on the concept of digital twins (DTs) is presented. The free-radical polymerization of vinyl monomers is considered to be a chain reaction consisting of a set of elementary ones. Those three types, related to the polymerization initiation and propagation as well as to the termination of polymer chain growth, are discussed. Special sets of DTs, whose total number approaches 60, distinguish each reaction type. The calculations are carried out using a semi-empirical version of the unrestricted Hartree-Fock approximation. The main energy and spin-density parameters of the ground state of the DTs are determined. The barrier profiles of two pairs of DTs are calculated, based on which two Evans-Polanyi-Semenov relations, attributed to elementary reactions of type (1) and (2), are constructed. These provide a quite reliable evaluation of the activation energy for the initiation and propagation of the free-radical polymerization of vinyl monomers in all the cases. The decisive role of spins in the formation of the elementary reaction transition states is established.

Porous Polymeric Catalysts Constructed from Vinylated Functionalities

ConspectusPorous organic polymers (POPs) have revolutionized the production of advanced catalytic materials with unique features such as a large surface area, tunable pore structure, ease of functionalization with a wide range of functional groups, and the ability to function as hosts for encapsulation of functional species, making them appealing for task-specific applications. Although numerous POP-based catalysts have been developed, they are rarely used as a common tool for preparatory-scale operations in laboratories. The high costs of these materials, because of the expensive reagents and catalysts often used in coupling reactions during their synthesis, primarily hinder their adoption. Since its discovery, free-radical polymerization of vinyl monomers to yield polymers has continuously attracted scientific and industrial attention and has been extensively adopted as an effective reaction for polymer production. Our group has targeted the synthesis of porous polymers via free-radical solvothermal polymerization of vinylated functionalities owing to the high efficiency, cost-effectiveness, and general applicability. More significantly, because of the flexibility of alkyl chains derived from the polymerized vinyl groups, the resulting frameworks are highly flexible, which is beneficial to facilitating the cooperation of catalytic components therein. Given the high catalytic efficiency of enzymes and amenable synthesis of POPs using vinylated functionalities, we have designed efficient heterogeneous catalysts by targeting the following aspects of enzyme mimicry: control over the second sphere of active sites, design of flexible ligand pockets, and construction of hydrophobic reaction microenvironments in POPs. In terms of control over the second sphere of active sites, we proposed the introduction of auxiliary groups or solvation environments via customized synthesis of POPs to perturb reaction pathways, reduce activation energies, and consequently improve catalytic performance. In terms of the design of flexible ligand pockets, we proposed the design concept of “porous ligand sponges” to fabricate quasi-homogeneous organometallic catalysts. The spatial continuity of the ligands on the flexible polymer chains enables their cooperation during catalysis, addressing the long-term challenges posed by the degradation of the catalytic performance after their heterogeneity, thus providing a possible replacement for homogeneous organometallic catalysts. In terms of adjusting the reaction microenvironments, we proposed the creation of hydrophobic environments to concentrate hydrophobic reagents in the vicinity of active sites and repel hydrophilic products to facilitate catalytic transformation.This Account highlights our ongoing research on the construction of POP-based catalysts. We also discuss the design strategies and principles involved with the aim of underscoring the unique features of POPs fabricated via solvothermal free-radical polymerization of vinylated functionalities in designing catalytic materials. This article summarizes our more than a decade of innovation in this field and is anticipated to advance the development of genuinely competitive artificial enzymes.

Non-Conjugated Polymer as an Efficient Dopant-Free Hole-Transporting Material for Perovskite Solar Cells.

A new non-conjugated polymer (PVCz-OMeDAD) with good solution processability was developed to serve as an efficient dopant-free hole-transporting material (HTM) for perovskite solar cells (PSCs). PVCz-OMeDAD was simply prepared by the free-radical polymerization of vinyl monomers, which were synthesized from low-cost raw materials through three high-yield synthesis steps. The combination of the flexible non-conjugated polyvinyl main chain and hole-transporting methoxydiphenylamine-substituted carbazole side chains endowed PVCz-OMeDAD with excellent film-forming ability, a suitable energy level, and high hole mobility. As a result, by using an ultra-thin (≈30 nm) PVCz-OMeDAD film as cost-effective dopant-free polymer HTM, the conventional n-i-p-type PSCs demonstrated a power conversion efficiency (PCE) up to 16.09 %, suggesting the great potential of the polymer film for future low-cost, large-scale, flexible PSCs applications.

η5-cyclopentadienyl-η2-styrenedicarbonylmanganese for initiation of free-radical polymerization of vinyl monomers

The polymerization of styrene, methyl methacrylate, and vinyl chloride catalyzed by η5-cyclopentadienyl-η2-styrenedicarbonylmanganese is studied. It is shown that the cyclopentadienyl complex of manganese containing the monomer ligand (styrene) in the coordination sphere can initiate the radical polymerization of vinyl monomers in a mild temperature range. On the basis of the experimental data and the quantum-chemical simulation of the initial stages of the process, schemes describing the initiation of polymerization under the action of the complex under study and the binary initiating system containing carbon tetrachloride are advanced. In the latter case, additional acceleration of the reaction is related to the interaction of carbon tetrachloride with the triplet form of the manganese complex that yields trichloromethyl radicals initiating polymerization.

Three-dimensional free-radical polymerization of vinyl monomers in the presence of oxygen as a new method of preparing hyperbranched polymers: A theoretical calculation

Hyperbranched macromolecules have been first synthesized by the three-dimensional free-radical polymerization of vinyl monomers in the presence of oxygen, which is known to be a strong inhibitor of freeradical chain processes. The inhibition of free-radical polymerization by molecular oxygen results in the shortening of primary polymer chains with pendant double bonds. As a consequence, the formation of insoluble gel, which develops at conversions of less than 1%, when the crosslinking free-radical polymerization is carried out under ordinary conditions, may be avoided up to a conversion of 100%. In terms of the kinetic scheme, including nearly 100 elementary reactions, the effects of temperature and concentration of reagents on the kinetic parameters of the process and the structural parameters of hyperbranched polymers based on methacrylate and styrene-like monomers have been studied. Optimal conditions that make it possible to synthesize hyperbranched polymers of the desired architecture and functionality at a sufficiently high yield, which are specified by the occurrence of oxygen-containing groups in primary polymer chains and at its ends, have been estimated.

Dicyclopentadienyltitanium chlorides as regulators of free-radical polymerization of vinyl monomers

The free-radical polymerization of styrene and methyl methacrylate in the presence of dicyclopentadienyltitanium chloride and dicyclopentadienyltitanium dichloride has been studied. It has been shown that the process proceeds without autoacceleration up to high conversions and is characterized by a linear increase in molecular mass with conversion. On the basis of quantum chemical calculations and ESR spectroscopic data, a scheme describing the growth of polymer chains with participation of organotitanium compounds is proposed.

Free-radical polymerization of vinyl monomers using hematin as a biomimetic catalyst in place of enzyme

This paper reports the free-radical polymerization of vinyl monomers catalyzed by hematin. The polymerization of methyl methacrylate (MMA) was carried out in the presence of hematin and H2O2, giving polyMMA, quantitatively. In the case of the polymerization of styrene and acrylamide, 2,4-pentanedione as a radical mediator was required in addition to hematin and H2O2. The polymerization of styrene reached an upper limit, whereas that of acrylamide proceeded in an almost quantitative conversion.

60Co γ-Irradiation-Initiated “Living” Free-Radical Polymerization in the Presence of Dibenzyl Trithiocarbonate

The free-radical polymerization of vinyl monomers in the presence of dibenzyl trithiocarbonate (DBTTC) and under 60 Co γ-irradiation is of living character. Under 60 Co irradiation, the bonds between benzyl group and sulfur were cleaved, benzyl radicals initiate the polymerization. The propagating radical together with trithiocarbonate radicals form a dormant polymer chain. The fast equilibrium between propagation radical and dormant polymer chain controls the polymerization.

Catalytic radical polymerization of vinyl monomers by cobalt porphyrin complex and metamorphosis of block-into-block copolymer

This is the first report on the catalytic room temperature free-radical polymerization of vinyl monomers, namely styrene (STY) and methyl methacrylate (MMA) using Co(II)TPP(Py) and aerial oxygen as a catalyst and a co-catalyst, respectively. The mechanism of polymerization has been investigated using 1H NMR, differential scanning calorimeter (DSC), thermogravimetric (TGA) and gel permeation chromatography (GPC) analysis and a radical pathway for the polymer formation is proposed. The rate of polymerization for the synthesis of active polymers of STY is higher than that of MMA, which has also been supported by computational studies. The active polymer, polystyrene (PS)–poly(styrene peroxide) (PSP) was also used for the synthesis of another block copolymer, PS-b-PMMA, by reacting PS–PSP with MMA. The mechanism of block copolymerization is discussed.

Synthesis of Novel Polymer-Silica Colloidal Nanocomposites via Free-Radical Polymerization of Vinyl Monomers

Polymer nanocomposites can exhibit unusual properties, and potential applications include catalyst supports and abrasion-resistant coatings. The copolymerization of 4-vinylpyridine in the presence of ultrafine silica sol is reported here to give rise to stable colloidal dispersions of polymer–silica nanocomposites which display a distinctive “currant bun” morphology (see Figure) in contrast to previously reported “raspberry” morphologies.

Synthesis of Novel Polymer–Silica Colloidal Nanocomposites via Free-Radical Polymerization of Vinyl Monomers

Polymer nanocomposites can exhibit unusual properties, and potential applications include catalyst supports and abrasion-resistant coatings. The copolymerization of 4-vinylpyridine in the presence of ultrafine silica sol is reported here to give rise to stable colloidal dispersions of polymer–silica nanocomposites which display a distinctive “currant bun” morphology (see Figure) in contrast to previously reported “raspberry” morphologies.

Highly Efficient Ruthenium-Based Catalytic Systems for the Controlled Free-Radical Polymerization of Vinyl Monomers.

A new set of ruthenium complexes such as 1 and 2 (the Grubbs ruthenium-carbene complex) has been shown to mediate the controlled atom-transfer radical polymerization (ATRP) of vinyl monomers with exceptional efficiency. Furthermore, there is a striking parallelism between the catalytic activity of these compounds in olefin metathesis and in ATRP.

Fotoiniciação de polimerização vinílica

The initiation step of the light-induced polymerization kinetics of vinyl monomers using dye-sensitized photoinitiators to generate active radicals is discussed. The photoredox processes of basic dyes with amines and sulfinates are described as photochemical systems capable of starting free-radical polymerization of vinyl monomers in homogeneous and microheterogeneous media. Photophysical techniques like laser flash photolysis and time-correlated single photon counting are used to investigate the excited-state kinetics of the dyes.

Effects of initiator loss by chain transfer in free-radical polymerization using batch operations

In the free-radical polymerization of vinyl monomers, initiator can be lost by chain transfer. This loss affects the monomer conversion with time in a batch reactor and can influence the expected molecular mass of the polymer as the reaction proceeds. Expressions are developed which allow these effects to be quantified. Examples indicate when these effects are important. The instantaneous number-average degree of polymerization passes through a minimum as the initiator concentration is increased. The location of this minimum depends on the importance of initiator loss by chain transfer. Initial monomer concentration affects the absolute value of molecular mass but has little influence on the relative effects of initiator loss by chain transfer.

Polymerization with organoboron compounds

AbstractIn the presence of organoboron compounds, free‐radical polymerization of vinyl monomers can proceed in spite of the presence of excess of typical radical inhibitors. The concept of free radical–organoboron complex formation is introduced to explain the unique role of organoboron compounds in such a polymerization system.

Effect of Zinc Chloride on the Velocity Coefficients in the Polymerization of Methyl Methacrylate

IT is well known that the reactivity of the propagating species in ionic polymerization is greatly influenced by the proximity and character of the gegenions and by complex formation. As a rule, free radical reactions are comparatively insensitive to the nature of their environment, although there are references in the literature to changes in the rate of free-radical polymerizations, and the nature of the polymers formed, which have been attributed to the participation of radicals in complexed forms. The investigation of the structure and reactivity of radical complexes in polymerization is a field which has not been surveyed systematically, but which, nevertheless, may contain interesting features. We have embarked on an investigation of the absolute rate coefficients in the free-radical polymerization of vinyl monomers in the presence of possible complexing agents and report here some results for the methyl methacrylate–zinc chloride system. The only measurements of a similar type recorded in the literature appear to be those of Bamford, Jenkins and Johnston1, on acrylonitrile in NN-dimethylformamide solution in the presence of lithium salts. Kargin, Kabanov and Zubov2 considered that the presence of zinc chloride during the polymerization of methyl methacrylate affects the microstructure of the polymer, but this finding was not confirmed by Bovey3. More recently, Imoto, Otsu and Harada4 have investigated the steady-state polymerization of methyl methacrylate in the presence of zinc chloride and have shown that at 60° C the rate of the reaction initiated by azo-bis-isobutyronitrile is increased by addition of zinc chloride, the ratio kp/√(kt) also being increased (kp, kt are the velocity coefficients for propagation and total bimolecular termination, respectively).