Showing papers on "Polymerization published in 2013"
TL;DR: This work reviews the progress that has been made in making sequence-controlled polymers of increasing length and complexity and proposes some strategies for controlling sequences in chain-growth and step-growth polymerizations.
Abstract: Background During the last few decades, progress has been made in manipulating the architecture of synthetic polymer materials. However, the primary structure—that is, the sequential arrangement of monomer units in a polymer chain—is generally poorly controlled in synthetic macromolecules. Common synthetic polymers are usually homopolymers, made of the same monomer unit, or copolymers with simple chain microstructures, such as random or block copolymers. These polymers are used in many areas but do not have the structural and functional complexity of sequence-defined biopolymers, such as nucleic acids or proteins. Indeed, monomer sequence regulation plays a key role in biology and is a prerequisite for crucial features of life, such as heredity, self-replication, complex self-assembly, and molecular recognition. In this context, developing synthetic polymers containing controlled monomer sequences is an important area for research. Precise molecular encoding of synthetic polymer chains. In most synthetic copolymers, monomer units (represented here as colored square boxes A, B, C, and D) are distributed randomly along the polymer chains (left). In sequence-controlled polymers, they are arranged in a specific order in all of the chains (right). Monomer sequence regularity strongly influences the molecular, supramolecular, andmacroscopic properties of polymer materials. Advances Various synthetic methods for controlling monomer sequences in polymers have been identified, and two major trends in the field of sequence-controlled polymers have emerged. Some approaches use biological concepts that have been optimized by nature for sequence regulation. For instance, DNA templates, enzymes, or even living organisms can be used to prepare sequence-defined polymers. These natural mechanisms can be adapted to tolerate nonnatural monomers. The other trend is the preparation of sequence-controlled polymers by synthetic chemistry. In the most popular approach, monomer units are attached one by one to a support, which is an efficient method but demanding in practice. Recently, some strategies have been proposed for controlling sequences in chain-growth and step-growth polymerizations. These mechanisms usually allow fast and large-scale synthesis of polymers. Specific kinetics and particular catalytic or template conditions allow sequence regulation in these processes. Outlook The possibility of controlling monomer sequences in synthetic macromolecules has many scientific and technological implications. Information can be controlled at the molecular level in synthetic polymer chains. This opens up interesting perspectives for the field of data storage. In addition, having power over monomer sequences could mean structural control of the resulting polymer, as it strongly influences macromolecular folding and self-assembly. For instance, functional synthetic assemblies that mimic the properties of globular proteins, such as enzymes and transporters, can be foreseen. Moreover, monomer sequence control influences some macroscopic properties. For example, bulk properties such as conductivity, rigidity, elasticity, or biodegradability can be finely tuned in sequence-controlled polymers. The behavior of polymers in solution, particularly in water, is also strongly dependent on monomer sequences. Thus, sequence regulation may enable a more effective control of structure-property relations in tomorrow’s polymer materials.
1,008 citations
TL;DR: In this article, a comprehensive review of NMP is presented, from its discovery to 2012, covering all aspects, features and achievements of the NMP, from synthetic approaches to nitroxides and alkoxyamines, kinetic aspects and polymerization features.
1,002 citations
TL;DR: The main achievements in nitroxide-mediated polymerization (NMP) from its discovery to late 2010 are discussed in this paper, where various synthetic approaches to nitroxides and alkoxyamines are first presented.
987 citations
TL;DR: This Review describes successful 2D polymerization strategies, as well as seminal research that inspired their development, and describes the early application targets of 2D polymers, each of which might benefit from predictable long-range molecular organization inherent to this macromolecular architecture.
Abstract: Two-dimensional polymers, which exhibit periodic bonding in two orthogonal directions, offer mechanical, electronic and structural properties distinct from their linear or irregularly crosslinked polymer counterparts. Their potential is largely unexplored because versatile and controlled synthetic strategies are only now emerging. This Review describes recent developments in two-dimensional polymerization methods.
800 citations
TL;DR: In this paper, a monomer approach for renewable polymers is presented, which is based on the assumption that natural molecular biomass plays an important role in the field of polymers and can be directly used or derivatized as monomers for controlled polymerization, in a way similar to many petroleum-derived monomers.
Abstract: Natural molecular biomass plays an important role in the field of renewable polymers, as they can be directly used or derivatized as monomers for controlled polymerization, in a way similar to many petroleum-derived monomers. We deliver this perspective primarily based on a monomer approach. Biomass-derived monomers are separated into four major categories according to their natural resource origins: (1) oxygen-rich monomers including carboxylic acids (lactic acid, succinic acid, itaconic acid, and levulinic acid) and furan; (2) hydrocarbon-rich monomers including vegetable oils, fatty acids, terpenes, terpenoids and resin acids; (3) hydrocarbon monomers (bio-olefins); and (4) non-hydrocarbon monomers (carbon dioxide). A variety of emerging synthetic tools (controlled polymerization and click chemistry) are particularly summarized. An overview on future opportunities and challenges, which are critical to promote biorefinery in the production of renewable chemicals and polymers, is given.
421 citations
TL;DR: Antimicrobial polymers grafted or self-assembled to inert or non inert vehicles can yield hybrid antimicrobial nanostructures or films, which can act as antimicrobials by themselves or deliver bioactive molecules for a variety of applications.
Abstract: Cationic compounds are promising candidates for development of antimicrobial agents. Positive charges attached to surfaces, particles, polymers, peptides or bilayers have been used as antimicrobial agents by themselves or in sophisticated formulations. The main positively charged moieties in these natural or synthetic structures are quaternary ammonium groups, resulting in quaternary ammonium compounds (QACs). The advantage of amphiphilic cationic polymers when compared to small amphiphilic molecules is their enhanced microbicidal activity. Besides, many of these polymeric structures also show low toxicity to human cells; a major requirement for biomedical applications. Determination of the specific elements in polymers, which affect their antimicrobial activity, has been previously difficult due to broad molecular weight distributions and random sequences characteristic of radical polymerization. With the advances in polymerization control, selection of well defined polymers and structures are allowing greater insight into their structure-antimicrobial activity relationship. On the other hand, antimicrobial polymers grafted or self-assembled to inert or non inert vehicles can yield hybrid antimicrobial nanostructures or films, which can act as antimicrobials by themselves or deliver bioactive molecules for a variety of applications, such as wound dressing, photodynamic antimicrobial therapy, food packing and preservation and antifouling applications.
400 citations
TL;DR: A simple and scalable method is described that enables the synthesis of sequence-controlled multiblock copolymers with precisely defined high-order structures, covering a wide range of functional groups, and paves the way to the design and synthesis of a new generation of synthetic polymers.
Abstract: A long-standing challenge in polymer chemistry has been to prepare synthetic polymers with not only well-defined molecular weight, but also precisely controlled microstructure in terms of the distribution of monomeric units along the chain. Here we describe a simple and scalable method that enables the synthesis of sequence-controlled multiblock copolymers with precisely defined high-order structures, covering a wide range of functional groups. We develop a one-pot, multistep sequential polymerization process with yields >99%, giving access to a wide range of such multifunctional multiblock copolymers. To illustrate the enormous potential of this approach, we describe the synthesis of a dodecablock copolymer, a functional hexablock copolymer and an icosablock (20 blocks) copolymer, which represents the largest number of blocks seen to date, all of very narrow molecular weight distribution for such complex structures. We believe this approach paves the way to the design and synthesis of a new generation of synthetic polymers.
368 citations
TL;DR: In this article, the synthesis, self-assembly and properties of well-defined polyhedral oligomeric silsequioxane (POSS) based hybrid polymers are reviewed.
328 citations
TL;DR: A broad overview of the development and evolution of post-polymerization modification reactions can be found in this paper, where the authors provide an overview of eight main classes of reactions.
Abstract: With a span as long as the history of polymer science itself, post-polymerization modification represents a versatile platform for the preparation of diversely functionalized polymers from a single precursor. Starting with the initial efforts by Staudinger in the 1920s, many of the early developments in modern polymer science can be attributed to the utilization of post-polymerization modification reactions. The scope of post-polymerization modification has greatly expanded since the 1990s due to the development of functional group tolerant controlled/living polymerization techniques combined with the (re)discovery of highly efficient coupling chemistries that allow quantitative, chemoselective, and orthogonal functionalization of reactive polymer precursors. After some basic mechanistic considerations, this Highlight will provide an overview of the development and evolution of eight main classes of post-polymerization modification reactions. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
325 citations
TL;DR: In this paper, the authors report a novel strategy to improve the interface between the high dielectric constant nanoparticles (i.e., BaTiO3) and ferroelectric polymer.
Abstract: Polymer nanocomposites with high energy density and low dielectric loss are highly desirable in electronic and electric industry. Achieving the ability to tailor the interface between polymer and nanoparticle is the key issue to realize desirable dielectric properties and high energy density in the nanocomposites. However, the understanding of the role of interface on the dielectric properties and energy density of polymer nanocomposites is still very poor. In this work, we report a novel strategy to improve the interface between the high dielectric constant nanoparticles (i.e., BaTiO3) and ferroelectric polymer [i.e., poly(vinylidene fluoride-co-hexafluoro propylene)]. Core–shell structured BaTiO3 nanoparticles either with different shell thickness or with different molecular structure of the shell were prepared by grafting two types of fluoroalkyl acrylate monomers via surface-initiated reversible addition–fragmentation chain transfer (RAFT) polymerization. The dielectric properties and energy storage c...
318 citations
TL;DR: This review focuses on those synthetic pathways that build up a polymer chain from ethene/propene and functionalised polar vinyl monomers, and polymerisation of alternative functionalised monomers is explored.
Abstract: Functional polyolefins (i.e., polyethene or polypropene bearing functional groups) are highly desired materials, due to their beneficial surface properties. Many different pathways exist for the synthesis of these materials, each with its own advantages and drawbacks. This review focuses on those synthetic pathways that build up a polymer chain from ethene/propene and functionalised polar vinyl monomers. Despite many recent advances in the various fields of olefin polymerisation, it still remains a challenge to synthesise high molecular-weight copolymers with tuneable amounts of functional groups, preferably with consecutive insertions of polar monomers occurring in a stereoselective way. To overcome some of these challenges, polymerisation of alternative functionalised monomers is explored as well.
TL;DR: The field of ring opening polymerization (ROP) has been a rapidly growing and industrially important area of research as discussed by the authors, and the literature up to 2012 has been considered but the citations refer to detailed reviews and key papers describing not only the latest developments but also the evolution of the current state of the art.
Abstract: This short, introductory review covers the still rapidly growing and industrially important field of ring opening polymerization (ROP). The review is organized according to mechanism (radical ROP (RROP), cationic ROP (CROP), anionic ROP (AROP) and ring-opening metathesis polymerization (ROMP)) rather than monomer classes. Nevertheless, the different groups of cyclic monomers are considered (olefins, ethers, thioethers, amines, lactones, thiolactones, lactams, disulfides, anhydrides, carbonates, silicones, phosphazenes and phosphonites) and the mechanisms by which they can be polymerized involving a ring-opening polymerization. Literature up to 2012 has been considered but the citations selected refer to detailed reviews and key papers, describing not only the latest developments but also the evolution of the current state of the art.
TL;DR: In this paper, several typical systems for RAFT dispersion polymerization are presented in detail and the factors influencing the polymerization and the in situ self-assembly are also highlighted in a minireview.
TL;DR: The present study demonstrates a novel approach for the fabrication of a highly hydrophilic PVDF UF membrane via postfabrication tethering of superhydrophilic silica nanoparticles (NPs) to the membrane surface and suggests promising applications of the postFabrication surface modification technique in various membrane separation areas.
Abstract: Polyvinylidene fluoride (PVDF) has drawn much attention as a predominant ultrafiltration (UF) membrane material due to its outstanding mechanical and physicochemical properties. However, current applications suffer from the low fouling resistance of the PVDF membrane due to the intrinsic hydrophobic property of the membrane. The present study demonstrates a novel approach for the fabrication of a highly hydrophilic PVDF UF membrane via postfabrication tethering of superhydrophilic silica nanoparticles (NPs) to the membrane surface. The pristine PVDF membrane was grafted with poly(methacrylic acid) (PMAA) by plasma induced graft copolymerization, providing sufficient carboxyl groups as anchor sites for the binding of silica NPs, which were surface-tailored with amine-terminated cationic ligands. The NP binding was achieved through a remarkably simple and effective dip-coating technique in the presence or absence of the N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide ...
TL;DR: A new approach to perform single-electron transfer living radical polymerization (SET-LRP) in water is described, which provides an extremely powerful tool for the synthesis of functional water-soluble polymers with controlled chain length and narrow molecular weight distributions.
Abstract: A new approach to perform single-electron transfer living radical polymerization (SET-LRP) in water is described. The key step in this process is to allow full disproportionation of CuBr/Me6TREN (TREN = tris(dimethylamino)ethyl amine to Cu(0) powder and CuBr2 in water prior to addition of both monomer and initiator. This provides an extremely powerful tool for the synthesis of functional water-soluble polymers with controlled chain length and narrow molecular weight distributions (polydispersity index approximately 1.10), including poly(N-isopropylacrylamide), N,N-dimethylacrylamide, poly(ethylene glycol) acrylate, 2-hydroxyethyl acrylate (HEA), and an acrylamido glyco monomer. The polymerizations are performed at or below ambient temperature with quantitative conversions attained in minutes. Polymers have high chain end fidelity capable of undergoing chain extensions to full conversion or multiblock copolymerization via iterative monomer addition after full conversion. Activator generated by electron tra...
TL;DR: In this article, a bio-based polymer network was generated by cross-laying soybean oil (ESO) with an aqueous citric acid (CA) solution without the addition of any other catalyst or solvent.
TL;DR: In this review, a general introduction into the categories of precipitation polymerization and their mechanisms is presented and the precise control of particle size, size distribution, pore size, morphology and surface chemistry of micro- and nanoparticles, core-shell hybrids and polymer hollow structures is discussed.
Abstract: Functional polymer micro- and nanoparticles with novel morphology are of great importance because of their wide range of applications in complex biological systems and nanotechnology. Due to the outstanding advantage of the absence of any surfactant, precipitation polymerization as a heterogeneous polymerization technique has been developed to prepare various uniform and clean polymer particles, such as microspheres, nanoparticles, core–shell particles, core–double shell particles, single-shell hollow particles, double-shell hollow particles, and rattle-type hollow nanostructures. In this review, a general introduction into the categories of precipitation polymerization and their mechanisms is presented. The precise control of particle size, size distribution, pore size, morphology and surface chemistry of micro- and nanoparticles, core–shell hybrids and polymer hollow structures is discussed. The development of complex nanostructures and their applications in separation, drug delivery and nano-reactor systems are highlighted as well.
TL;DR: The high surface area graphene nanosheets as dispersed phase in polymeric nanocomposites showed significant improvement in thermal stability and electrical conductivity.
TL;DR: This Focus Review describes how the development of RAFT and RAFT application has been facilitated by the adoption of continuous flow techniques using tubular reactors and through the use of high-throughput methodology.
Abstract: Reversible addition-fragmentation chain transfer (RAFT) is one of the most robust and versatile methods for controlling radical polymerization. With appropriate selection of the RAFT agent for the monomers and reaction conditions, it is applicable to the majority of monomers subject to radical polymerization. The process can be used in the synthesis of well-defined homo-, gradient, diblock, triblock, and star polymers and more complex architectures, which include microgels and polymer brushes. In this Focus Review we describe how the development of RAFT and RAFT application has been facilitated by the adoption of continuous flow techniques using tubular reactors and through the use of high-throughput methodology. Applications described include the use of RAFT in the preparation of polymers for optoelectronics, block copolymer therapeutics, and star polymer rheology control agents.
TL;DR: In this paper, a thin-film selective layer of the composite hollow fiber was formed through interfacial polymerization on the inner surface of a polyethersulfone (PES) ultrafiltration (UF) membrane substrate with branched polyethyleneimine (PEI) and trymesoyl chloride (TMC) employed as the monomers in aqueous and organic phases, respectively.
TL;DR: In this article, a more asymmetric diblock copolymer formulation is presented, which is the first time that higher order morphologies (e.g. worms and vesicles) have been accessed in non-polar solvents and is expected to have potential boundary lubrication applications for engine oils.
Abstract: Well-defined poly(lauryl methacrylate-benzyl methacrylate) (PLMA-PBzMA) diblock copolymer nanoparticles are prepared in n-heptane at 90 °C via reversible addition–fragmentation chain transfer (RAFT) polymerization. Under these conditions, the PLMA macromolecular chain transfer agent (macro-CTA) is soluble in n-heptane, whereas the growing PBzMA block quickly becomes insoluble. Thus this dispersion polymerization formulation leads to polymerization-induced self-assembly (PISA). Using a relatively long PLMA macro-CTA with a mean degree of polymerization (DP) of 37 or higher leads to the formation of well-defined spherical nanoparticles of 41 to 139 nm diameter, depending on the DP targeted for the PBzMA block. In contrast, TEM studies confirm that using a relatively short PLMA macro-CTA (DP = 17) enables both worm-like and vesicular morphologies to be produced, in addition to the spherical phase. A detailed phase diagram has been elucidated for this more asymmetric diblock copolymer formulation, which ensures that each pure phase can be targeted reproducibly. 1H NMR spectroscopy confirmed that high BzMA monomer conversions (>97%) were achieved within 5 h, while GPC studies indicated that reasonably good blocking efficiencies and relatively low diblock copolymer polydispersities (Mw/Mn < 1.30) were obtained in most cases. Compared to prior literature reports, this all-methacrylic PISA formulation is particularly novel because: (i) it is the first time that higher order morphologies (e.g. worms and vesicles) have been accessed in non-polar solvents and (ii) such diblock copolymer nano-objects are expected to have potential boundary lubrication applications for engine oils.
TL;DR: In this article, the synthesis, crystal structure, and physicomechanical properties of a biobased polyester prepared from 2,5-furandicarboxylic acid (FDCA) and 1,4-butanediol were described.
Abstract: This paper describes the synthesis, crystal structure, and physicomechanical properties of a biobased polyester prepared from 2,5-furandicarboxylic acid (FDCA) and 1,4-butanediol. Melt-polycondensation experiments were conducted by a two-stage polymerization using titanium tetraisopropoxide (Ti[OiPr]4) as a catalyst. Polymerization conditions (catalyst concentration, reaction time and second stage reaction temperature) were varied to optimize poly(butylene-FDCA), PBF, and molecular weight. A series of PBFs with different Mw were characterized by DSC, TGA, DMTA, X-ray diffraction and tensile testing. Influence of molecular weight and melting/crystallization enthalpy on PBF material tensile properties was explored. Cold-drawing tensile tests at room temperature for PBF with Mw 16K to 27K showed a brittle-to-ductile transition. When Mw reaches 38K, the Young modulus of PBF remains above 900 MPa, and the elongation at break increases to above 1000%. The mechanical properties, thermal properties and crystal st...
TL;DR: The observation of considerably lengthy individual supramolescular polymer molecules indicates that the molecular self-assembly in water by non-covalent host-guest molecular recognition is sufficiently strong to form the supramolecular polymer.
Abstract: A light-driven, linear, chiral supramolecular polymer was constructed in water by host–guest molecular recognition between bis(p-sulfonatocalix[4]arene) and the α-cyclodextrin-based pseudo[3]rotaxane containing axially chiral 1,1′-binaphthyl and photoresponsive azobenzene moieties. The successful supramolecular polymerization by non-covalent host–guest molecular recognition was confirmed by 1H NMR spectroscopy and dynamic light scattering (DLS) measurements, and its photoresponsive behavior was investigated by UV–vis absorption spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The chirality of this supramolecular polymer was confirmed by circular dichroism spectroscopy. The dramatic morphology change of this chiral polymer driven by light was observed in SEM, AFM and TEM images. More interestingly, dynamically self-assembled, light-driven, single-helical linear supramolecular polymer molecules with lengths of hundreds of nanometers...
TL;DR: The high anticoagulant ability of Hep-g-pRGO indicates that the grafted biopolymer could maintain its biological activity after immobilization onto the surface of pRGO, suggesting that the biopolymers functionalized RGO has good cytocompatibility for HUVEC cells.
Abstract: A green and facile method for preparing biopolymer functionalized reduced graphene oxide (RGO) by using mussel inspired dopamine (DA) as the reducing reagent and the functionalized molecule is proposed. In the study, GO is reduced by DA and DA is adhered to RGO by one-step pH-induced polymerization of DA (polydopamine, PDA), and then heparin or protein is grafted onto the PDA adhered RGO (pRGO) through catechol chemistry. The obtained pRGO, heparin grafted pRGO (Hep-g-pRGO), and BSA grafted pRGO (BSA-g-pRGO) exhibit fine 2D morphology and excellent stability in water and PBS solution. Furthermore, the biocompatibility of the biopolymer functionalized RGO are investigated using human blood cells and human umbilical vein endothelial cells (HUVECs). The biopolymer functionalized RGO exhibits an ultralow hemolysis ratio (lower than 1.8%), and the cellular toxicity assay suggests that the biopolymer functionalized RGO has good cytocompatibility for HUVEC cells, even at a high concentration of 100 μg mL−1. Moreover, the high anticoagulant ability of Hep-g-pRGO indicates that the grafted biopolymer could maintain its biological activity after immobilization onto the surface of pRGO. Therefore, the proposed safe and green biomimetic method confers the biopolymer functionalized RGO with great potential for various biological and biomedical applications.
TL;DR: The tetrazine–norbornene inverse electron demand Diels–Alder reaction is introduced as a new cross-linking chemistry for the formation of cell laden hydrogels for tissue engineering applications.
TL;DR: Investigation of Initiated-CVD shows successful results in terms of rationally designed micro- and nanoengineered materials to control molecular interactions at material surfaces for organic conducting and semiconducting polymers.
Abstract: Well-adhered, conformal, thin (<100 nm) coatings can easily be obtained by chemical vapor deposition (CVD) for a variety of technological applications. Room temperature modification with functional polymers can be achieved on virtually any substrate: organic, inorganic, rigid, flexible, planar, three-dimensional, dense, or porous. In CVD polymerization, the monomer(s) are delivered to the surface through the vapor phase and then undergo simultaneous polymerization and thin film formation. By eliminating the need to dissolve macromolecules, CVD enables insoluble polymers to be coated and prevents solvent damage to the substrate. CVD film growth proceeds from the substrate up, allowing for interfacial engineering, real-time monitoring, and thickness control. Initiated-CVD shows successful results in terms of rationally designed micro- and nanoengineered materials to control molecular interactions at material surfaces. The success of oxidative-CVD is mainly demonstrated for the deposition of organic conducting and semiconducting polymers.
TL;DR: This is the first report where some control over the relative position of the sugars is exhibited and their binding to the human lectin DC-SIGN is demonstrated, which has implications for the controlled folding of synthetic macromolecules.
Abstract: Glycan–protein interactions are essential for many physiological processes including cell–cell recognition, cell adhesion, cell signalling, pathogen identification, and differentiation. Dendritic cell-specific intercellular adhesion molecule3-grabbing non-integrin (DC-SIGN; CD209) is a C-type lectin (carbohydrate-binding protein) present on both macrophages and dendritic cell subpopulations and plays a critical role in many cell interactions. DC-SIGN binds to microorganisms and host molecules by recognizing surface-rich mannose-containing glycans through multivalent glycan– protein interactions and serves as a target for several viruses, such as human immunodeficiency virus (HIV) and hepatitis C virus (HCV). Carbohydrate-binding proteins (CBP) have been suggested as potential microbicides for the prevention of HIV infection. However, the isolation of natural CBPs is relatively difficult because of their hydrophilic nature and low affinity for the virus. 4] Thus, synthetic lectins are of interest for carbohydrate recognition studies. Alternatively, noncarbohydrate inhibitors of mammalian lectins can be used to prevent the interaction between DC-SIGN and gp120. The structures of these multivalent ligands have a great effect on carbohydrate binding to lectins, and the use of linear polymers to effectively inhibit lectin binding has been demonstrated by several research groups. Synthetic polymer chemistry has developed rapidly in recent years. Currently, polymerization of functional monomers with the desired chain length, structure, and composition is straightforward; whereas producing polymers with monomer sequence control remains challenging, which has implications for the controlled folding of synthetic macromolecules. There are a few recent reports where sufficient control has been achieved in controlling the monomer sequence along the polymer chain. To the best of our knowledge, this is the first report where some control over the relative position of the sugars is exhibited and their binding to the human lectin DC-SIGN is demonstrated. We have used a controlled polymerization technique, single-electron transfer living radical polymerization (SET-LRP), to polymerize glycomonomers, which are prepared by copper catalyzed azide–alkyne click (CuAAC) reaction prior to polymerization. A series of glycomonomers were prepared by reaction of 3-azidopropylacrylate (APA) and alkylated mannose, glucose, and fucose using a Fischer–Helferich glycosylation. This was performed using CuSO4 and sodium ascorbate in a methanol/water mixture (see the Supporting Information). SET-LRP of the glucose monomer (GluA) was performed in dimethylsulfoxide (DMSO) using a copper(0)/copper(II) and tris[2-(dimethylamino)ethyl]amine (Me6TREN)-derived catalyst. Polymerization reached over 90 % monomer conversion in six hours whilst maintaining a narrow molecular weight distribution with increasing molecular weight. (Supporting Information, Figure S4). The obtained polymers were characterized by size exclusion chromatography (SEC) and MALDI-TOF mass spectroscopy (MS) or high-resolution electrospray ionization mass spectroscopy (HR-ESI MS), which indicated very high chain-end fidelity allowing for sequential monomer addition. We designed a polymerization reaction starting with one equivalent of initiator (I) and two equivalents of mannose glycomonomer (ManA; Figure 1a). ManA was fully consumed after 12 hours; then two equivalents of GluA in DMSO were added to the reaction mixture and GluA was consumed in 16 hours. Two equivalents of ManA in DMSO were subsequently added to the reaction mixture, and this cycle was continued until six short blocks of glycopolymers were produced (the degree of polymerization (DP) = 2 for each block, (mannose)2-(glucose)2-(mannose)2-(glucose)2(mannose)2-(glucose)2). No purification steps were required prior to addition of the subsequent monomer. The conversion of the first four blocks, as analyzed by H NMR spectroscopy, reached 100 %, shown by the complete disappearance of vinyl groups at 5.7–6.5 ppm. The glycomonomers were dissolved in purged DMSO prior to their addition and this resulted in further dilution of the reaction mixture upon each monomer addition. Traces of vinyl groups could still be detected after [*] Q. Zhang, J. Collins, A. Anastasaki, Dr. C. R. Becer, Prof. D. M. Haddleton Department of Chemistry, University of Warwick Gibbet Hill Road, Coventry, CV4 7AL (UK) E-mail: d.m.haddleton@warwick.ac.uk Homepage: http://www.warwick.ac.uk/go/polymers Dr. R. Wallis Department of Biochemistry, University of Leicester Leicester, LE1 9HN (UK) Dr. D. A. Mitchell Clinical Sciences Research Institute, Warwick Medical School, University of Warwick Coventry, CV2 2DX (UK) [**] We acknowledge financial support from the University of Warwick and the China Scholarship Council. Equipment used in this research was funded by the Innovative Uses for Advanced Materials in the Modern World (AM2) with support from AWM and ERDF. D.M.H. is a Royal Society/Wolfson Fellow and C.R.B. is a Science City Senior Research Fellow. Dr. Christopher N. Scanlan has provided the gp120. Supporting information for this article (syntheses of all materials and details of the characterization methods) is available on the WWW under http://dx.doi.org/10.1002/anie.201300068. Angewandte Chemie
TL;DR: N nanoporous polymers based on the vinylbenzyl chloride (VBC) monomer and the DVB cross-linking agent are reported, which are the first examples of ATRP initiators in which the initiator species is located within the framework of the mesoporous support.
Abstract: The world s oceans, where uranium is found quite uniformly at a concentration of 3.3 mgL , present an alternative source of uranium to terrestrial mining for nuclear fuel. Environmental concerns associated with mining will undoubtedly increase as reserves are depleted, thus increasing the utility of more environmentally friendly feedstocks. Hence, before terrestrial resources become scarce, the development of sorbents designed for seawater extraction is of strategic importance to guarantee future uranium resources. From the first inorganic adsorbents, which showed poor selectivity and mechanical resistance, to the most recent polyethylene-fiberbased sorbents containing amidoxime–carboxylic acid copolymers, and more recently layered metal sulfides and metal– organic frameworks, interest in uranium seawater extractions has continuously increased among governments worldwide. Because the concentration of uranium in the oceans is relatively low, maximization of the adsorption properties of sorbents, for example, through changes in their surface area and pore structure, can greatly improve the kinetics of uranium extraction and the adsorption capacity simultaneously. To facilitate the uptake of uranyl ions with fast kinetics, various sorbents containing the amidoxime group, such as hydrogels, particles and beads, membranes, macroporous fibers, and composites, have been prepared by suspension polymerization, radiation-induced grafting, and even sonochemical functionalization. However, silica beads and most carbon materials have a relatively small accessible surface area for the growth of large polymers or a low number of surface sites available for the grafting of functional groups. Thus, the design of substrates with large numbers of accessible reactive sites for the grafting of polymeric surface groups is necessary for the development of materials with improved uranium-adsorption capacity. Recently, porous polymers based on divinylbenzene (DVB) have been developed for applications in separations and catalysis. For example, the copolymerization of p-styrene sulfonate with divinylbenzene led to a catalytically active porous polymer. This method has the additional advantage that polymers can be obtained with controlled porosity and high surface areas without porogens. It is thus timeand cost-effective, as well as more environmentally friendly than the templated synthesis of carbonaceous materials. Motivated by these findings, we report herein nanoporous polymers based on the vinylbenzyl chloride (VBC) monomer and the DVB cross-linking agent. As well as a well-developed nanoporous structure of microand mesopores, the obtained polymers contain large numbers of accessible chlorine species, which can be used as initiators for atom-transfer radical polymerization (ATRP). These materials are the first examples of ATRP initiators in which the initiator species is located within the framework of the mesoporous support. The accessible framework and surface chlorine species were used to grow polyacrylonitrile chains, which were then converted into polyamidoxime for uranium adsorption from seawater with tailorable adsorption and surface properties. Three copolymer monoliths were synthesized by freeradical polymerization; that is, the monomer 4-vinylbenzyl chloride was cross-linked by divinylbenzene with 2,2’-azobisisobutyronitrile (AIBN, 98%) as the initiator to give copolymers hereafter referred to as p(xDVB-VBC) (in which x stands for the molar ratio of DVB to VBC). By varying the ratio of the monomer and the cross-linking reactant, it was possible to adjust the pore structure, that is, the surface area and pore volume (Figure 1). Since these adjustments arose from changes in the DVB to VBC ratio, the initiator concentration (i.e. the amount of chloride substituents present) was also varied. The nitrogen isotherms measured at 196 8C for the samples show that nonporous materials as well as materials with tailorable mesopore volumes can be [*] Dr. Y. Yue, Dr. R. T. Mayes, Dr. P. F. Fulvio, Dr. X.-G. Sun, Prof. Dr. S. Dai Chemical Sciences Division, Oak Ridge National Laboratory Oak Ridge, TN 37831 (USA) E-mail: dais@ornl.gov