Development of organotellurium-mediated and organostibine-mediated living radical polymerization reactions

Modern Trends in Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) is a powerful and versatile technique for producing colloidal dispersions of block copolymer particles with desired morphologies. Currently, PISA can be carried out in various media, over a wide range of temperatures, and using different mechanisms. This method enables the production of biodegradable objects and particles with various functionalities and stimuli sensitivity. Consequently, PISA offers a broad spectrum of potential commercial applications. The aim of this review is to provide an overview of the current state of rational synthesis of block copolymer particles with diverse morphologies using various PISA techniques and mechanisms. The discussion begins with an examination of the main thermodynamic, kinetic, and structural aspects of block copolymer micellization, followed by an exploration of the key principles of PISA in the formation of gradient and block copolymers. The review also delves into the main mechanisms of PISA implementation and the principles governing particle morphology. Finally, the potential future developments in PISA are considered.

Photoredox Catalysis in Photocontrolled Cationic Polymerizations of Vinyl Ethers

ConspectusAdvances in photocontrolled polymerizations have expanded the scope of polymer architectures and structures that can be synthesized for various applications. The majority of these polymerizations have been developed for radical processes, which limits the diversity of monomers that can be used in macromolecular design. More recent developments of photocontrolled cationic polymerizations have taken a step toward addressing this limitation and have expanded the palette of monomers that can be used in stimuli-regulated polymerizations, enabling the synthesis of previously inaccessible polymeric structures. This Account will detail our group's studies on cationic polymerization processes where chain growth is regulated by light and highlight how these methods can be combined with other stimuli-controlled polymerizations to precisely dictate macromolecular structure.Photoinitiated cationic polymerizations are well-studied and important processes that have control over initiation. However, we wanted to develop systems where we had spatiotemporal control over both polymer initiation and chain growth. This additional command over the reaction provides the ability to manipulate the growing polymer with an external stimulus during a polymerization, which can be used to control structure. To achieve this goal, we set out to develop a method to photoreversibly generate a cation at a growing chain end that could participate in a controlled polymerization process. We took inspiration from previous work on cationic degenerate chain transfer polymerizations of vinyl ethers that used thiocarbonylthio chain transfer agents. These polymerizations were initiated by a strong acid and gave well-defined poly(vinyl ether)s. We posited that we could remove the acid initiator in these systems and reversibly oxidize the thiocarbonylthio chain ends in these reactions with a photocatalyst to give a photocontrolled cationic polymerization of vinyl ethers. This Account will focus on our journey to discover cationic photocontrolled polymerizations. We will summarize our initial developments and detail our mechanistic understanding of these reactions using both organic and inorganic based photocatalysts, and we will outline more recent efforts to expand cationic degenerate chain transfer polymerizations to other thioacetal initiators. Finally, we will detail how these photocontrolled cationic polymerizations can be used to switch monomer selectivity in situ using light to control polymer structure. At the end of the Account, we will discuss our vision for future potential applications of these photocontrolled cationic polymerizations in the synthesis of novel block copolymers and next generation cross-linked networks.

Reversible chain transfer catalyzed polymerization in miniemulsion systems with tetraiodomethane as a catalyst

Tetraiodomethane (CI4) is an effective catalyst in reversible chain transfer catalyzed polymerization (RTCP) of methacrylate monomers in miniemulsion polymerization systems (miniemulsion RTCP).

Reversible-deactivation radical polymerization of vinyl acetate mediated by tralen, an organomediator

An organic compound, tralen, has been developed as a mediator to control the radical polymerization of vinyl acetate, methyl acrylate, and N-vinyl pyrrolidone via the reversible termination mechanism.

Molecular bismuth(iii) monocations: structure, bonding, reactivity, and catalysis

Structurally defined, molecular bismuth(iii) cations show remarkable properties in coordination chemistry, Lewis acidity, and redox chemistry, allowing for unique applications in synthetic chemistry.

Aluminum Tralen Complex Meditated Reversible-Deactivation Radical Polymerization of Vinyl Acetate

The Al^III(tralen)Cl complex (tralenH₂ = N,N'-di(cyclohepta-2,4,6-trien-1-one-2-yl)-1,2-diaminobenzene) has been synthesized and applied to mediate the reversible-deactivation radical polymerization (RDRP) of vinyl monomers. The polymerization of unconjugated monomers such as vinyl acetate (VAc) and N-vinylpyrrolidone (NVP) with Al^III(tralen)Cl showed the living characters of linearly increased molecular weight with conversion and formation of block copolymer. However, the control manners in the polymerization of conjugated monomers like acrylates and styrene were limited. The electron paramagnetic resonance (EPR) spectrum indicated that Al^III(tralen)BArF (BArF = tetrakis(3,5-trifluormethylphenyl)borate) and propagating radicals formed a paramagnetic dormant species, possibly PVAc-Al^III(tralen)BArF, via the single-electron transfer to the tralen ligand.

Generation of Alkyl Radicals: From the Tyranny of Tin to the Photon Democracy

Alkyl radicals are key intermediates in organic synthesis. Their classic generation from alkyl halides has a severe drawback due to the employment of toxic tin hydrides to the point that "flight from the tyranny of tin" in radical processes was considered for a long time an unavoidable issue. This review summarizes the main alternative approaches for the generation of unstabilized alkyl radicals, using photons as traceless promoters. The recent development in photochemical and photocatalyzed processes enabled the discovery of a plethora of new alkyl radical precursors, opening the world of radical chemistry to a broader community, thus allowing a new era of photon democracy.

Main-Group Metal Complexes in Selective Bond Formations Through Radical Pathways

Recent years have witnessed remarkable advances in radical reactions involving main-group metal complexes. This includes the isolation and detailed characterization of main-group metal radical compounds, but also the generation of highly reactive persistent or transient radical species. A rich arsenal of methods has been established that allows control over and exploitation of their unusual reactivity patterns. Thus, main-group metal compounds have entered the field of selective bond formations in controlled radical reactions. Transformations that used to be the domain of late transition-metal compounds have been realized, and unusual selectivities, high activities, as well as remarkable functional-group tolerances have been reported. Recent findings demonstrate the potential of main-group metal compounds to become standard tools of synthetic chemistry, catalysis, and materials science, when operating through radical pathways.

New Aspects on the Modeling of Dithiolactone-Mediated Radical Polymerization of Vinyl Monomers

A kinetic model for the dithiolactone-mediated radical polymerization of vinyl monomers based on the persistent radical effect and reversible addition (negligible fragmentation) was used to calculate the polymerization rate and describe molar mass development in the polymerization of methyl methacrylate at 60 °C, using 2,2-azobisisobutyronitrile (AIBN) as an initiator, as well as dihydro-5-phenyl-2(3H)-thiophenethione (DTL1) and dihydro-2(3H)-thiophenethione (DTL2) as controllers. The model was implemented in the PREDICI commercial software. A good agreement between experimental data and model predictions was obtained.

Polymer grafting on graphene layers by controlled radical polymerization

In situ controlled radical polymerization (CRP) is considered as an important approach to graft polymer brushes with controlled grafting density, functionality, and thickness on graphene layers. Polymers are tethered with chain end or through its backbone to the surface or edge of graphene layers with two in situ polymerization methods of "grafting from" and "grafting through" and also a method based on coupling reactions known as "grafting to". The "grafting from" method relies on the propagation of polymer chains from the surface- or edge-attached initiators. The "grafting through" method is based on incorporation of double bond-modified graphene layers into polymer chains through the propagation reaction. The "grafting to" technique involves attachment of pre-fabricated polymer chains to the graphene substrate. Here, physical and chemical attachment approaches are also considered in polymer-modification of graphene layers. Combination of CRP mechanisms of reversible activation, degenerative (exchange) chain transfer, atom transfer, and reversible chain transfer with various kinds of grafting reactions makes it possible to selectively functionalize graphene layers. The main aim of this review is assessment of the recent advances in the field of preparation of polymer-grafted graphene substrates with well-defined polymers of controlled molecular weight, thickness, and polydispersity index. Study of the opportunities and challenges for the future works in controlling of grafting density, site-selectivity in grafting, and various topologies of the brushes with potential applications in stimuli-responsive surfaces, polymer composites, Pickering emulsions, coating technologies, and sensors is also considered.

Synthesis and Nano-object Assembly of Biomimetic Block Copolymers for Catalytic Silver Nanoparticles

Biomimetic ABC triblock copolymers of poly[2-(methacryloyloxy)ethyl phosphorylcholine]- b-poly[2-(dimethylamino)ethyl methacrylate]- b-poly(2-hydroxypropyl methacrylate) (PMPC- b-PDMA- b-PHPMA) were synthesized by RAFT aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) in the presence of a PMPC- b-PDMA macromolecular chain transfer agent (macro-CTA). This ABC triblock copolymer deploys well-known biocompatible PMPC and PDMA for the coordination of Ag⁺ ions to form silver nanoparticles in situ on reduction, and PHPMA for assembling (core) in water. The synthesis of PMPC- b-PDMA- b-PHPMA starts when both the reactive steric stabilizer of PMPC₂₅- b-PDMA₄ macro-CTA and HPMA monomer are dissolved in water. The growing PHPMA is not soluble in water and begins to assemble based on three-layer onion micelles, in which the outer and inner shells are PMPC and PDMA, respectively. In the synthesis of PMPC₂₅- b-PDMA₄- b-PHPMA _z at a constant 25% (w/w) solids concentration, the resultant assemblies change from spheres to worms to jellyfishes to vesicles when the targeted PHPMA chain length increases from 100mer to 400mer at full monomer conversion. Furthermore, in the synthesis of identical PMPC₂₅- b-PDMA₄- b-PHPMA₄₀₀ copolymers, the assembly morphology can be controlled from vesicles to spheres through worms by varying the solids concentration in the polymerization mixture, decreasing from 25% (w/w) to 15% (w/w) at full monomer conversion. Thus, the final morphology can be tuned by the degree of polymerization of HPMA and the solids concentration in the polymerization mixture. Using the resultant three PMPC₂₅- b-PDMA₄- b-PHPMA₄₀₀ assemblies as scaffolds, Ag(0) nanoparticles (Ag-NPs) are obtained through in situ reduction of AgNO₃ facilitated by electrostatic interactions between the Ag⁺ ions and PDMA moieties. The resultant Ag-NPs loaded in the assemblies exhibit excellent stability, dispersibility, and activity of catalyst for the reduction of p-nitrophenol. The order of rate constants for the reduction using Ag-NPs loaded in the assemblies is worms > vesicles > spheres, which corresponds to the order of the surface areas of the assemblies of PMPC₂₅- b-PDMA₄- b-PHPMA₄₀₀. These results can be achieved thanks to the kinetically frozen PMPC₂₅- b-PDMA₄- b-PHPMA₄₀₀ assemblies with identical compositions.

Photoinduced Miniemulsion Atom Transfer Radical Polymerization

Photomediated atom transfer radical polymerization (photoATRP) of (meth)acrylic monomers was conducted in miniemulsion media. The polymerization procedures took advantage of an ion-pair catalyst formed by interaction of Cu/TPMA² (TPMA = tris(2-pyridylmethyl)amine) and an anionic surfactant, sodium dodecyl sulfate (SDS). The ion-pair catalyst was efficient in controlling ATRP reactions with catalyst loadings as low as 100 ppm. The effect of different polymerization parameters, such as the size of the reaction vial, amount of surfactant, and solids content influencing the photoATRP in miniemulsion, was studied. The polymerization was conducted with solids content ranging from 5 to 50 vol % under a moderate surfactant loading (<5 wt % relative to monomer). Excellent temporal control was achieved upon switching the UV light on and off multiple times, and the polymer was successfully chain extended, indicating high retention of chain-end fidelity.

Visible light-induced free radical promoted cationic polymerization using organotellurium compounds

In the present study, visible light and sunlight-induced cationic polymerization of vinyl and cyclic ethers using organotellurium compounds is demonstrated.

Improvement in Liquid Chromatographic Performance of Organic Polymer Monolithic Capillary Columns with Controlled Free-Radical Polymerization

Capillary columns containing butyl or lauryl methacrylate monoliths were prepared using two different free-radical polymerization methods: conventional free-radical polymerization and controlled/living free-radical polymerization, both initiated thermally, and these methods were compared for the first time. Both monolith morphology and chromatographic efficiency were compared for the synthesized stationary phases using scanning electronic microscopy (SEM) and capillary liquid chromatography, respectively. Columns prepared using controlled method gave better chromatographic performance for both monomers tested. The lauryl-based monolith showed 7-fold improvement in chromatographic efficiency with a plate count of 42,000 plates/m (corrected for dead volume) for a non-retained compound. Columns fabricated using controlled polymerization appeared more homogenous radially with fused small globular morphologies, evaluated by SEM, and lower column permeability. The columns were compared with respect to resolving power of a series of alkylbenzenes under isocratic and gradient elution conditions.

Efficient Pathway for Preparing Hollow Particles: Site-Specific Crosslinking of Spherical Polymer Particles with Photoresponsive Groups That Play a Dual Role in Shell Crosslinking and Core Shielding

Site-specific a posteriori photocrosslinking of homogeneous spherical polymer particles and subsequent removal of the particle core-the self-templating strategy-has been developed as an efficient pathway for hollow particle formation. In this approach, homogeneous polymer particles containing linear polymers bearing post-crosslinkable side-chain groups are first synthesized, and the photoinduced crosslinking occurred only at the shell region in the homogeneous polymer particles. Our fundamental studies clarified that the remaining non-crosslinked photoresponsive groups in the shell region played a crucial role in shielding the core region from photoirradiation. The shell-selective crosslinking was successfully applied to hollow polymer particle formation by core removal. This facile route to polymeric hollow particle formation via a self-templating strategy has great potential to be used as an alternative because the route has high mass productivity and high simplicity as a result of the non-use of additional sacrificial template particles and highly toxic solvents.

Redox Active Compounds in Controlled Radical Polymerization and Dye-Sensitized Solar Cells: Mutual Solutions to Disparate Problems

Controlled radical polymerization (CRP) and dye-sensitized solar cells (DSSCs) are two fields of research that at an initial glance appear to have little in common. However, despite their obvious differences, both in application and in scientific nature, a closer look reveals a striking similarity between many of the compounds widely used as control agents in radical polymerization and as redox couples in dye-sensitized solar cells. Herein, we review the various redox active compounds used and examine the characteristics that give them the ability to perform this dual function. In addition we explore the advances in the understanding of the structural features that enhance their activity in both CRP and DSSCs. It is hoped that such a comparison will be conducive to improving process performance in both fields.

Reversible chain transfer catalyzed polymerization (RTCP) in nitrogen-based solvents without additional catalysts

N,N-Dimethylformamide (DMF) andN-methyl-2-pyrrolidone (NMP) as typical nitrogen-based solvents were used as the catalyst for RTCP without additional catalyst, which could also be carried out in the presence of a limited amount of air.

High-molecular-weight polar acrylate block copolymers as high-performance dismantlable adhesive materials in response to photoirradiation and postbaking

Controlled synthesis of block copolymers as dismantlable adhesives using an organotellurium-mediated living radical polymerization (TERP) for discussion of adhesion strength and failure mode.