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Macromolecular Engineering through Click Chemistry and Other Efficient Transformations

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Abstract

Precision synthesis of advanced polymeric materials requires efficient, robust, and facile chemical reactions. Paradoxically, the synthesis of increasingly intricate macromolecular structures generally benefits from exploitation of the simplest reactions available. This idea, combined with requirements of high efficiency, orthogonality, and simplified purification procedures, has led to the rapid adoption of “click chemistry” strategies in the field of macromolecular engineering. This Perspective provides context as to why these newly developed or recently reinvigorated reactions have been so readily embraced for the preparation of polymers with advanced macromolecular topologies, increased functionality, and unique properties. By highlighting important examples that rely on click chemistry techniques, including copper(I)-catalyzed and strain-promoted azide−alkyne cycloadditions, Diels−Alder cycloadditions, and thiol−ene reactions, among others, we hope to provide a succinct overview of the current state of the art and future impact these strategies will have on polymer chemistry and macromolecular engineering.

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... Their attractive features include very high yields (quantitative), modularity, absence of toxic byproducts. [58][59][60][61] In addition to this, reactions such as Diels-Alder cycloaddition, [62,63] thiol Michael addition, [64,65] or strainpromoted azide-alkyne reaction [66,67] occur in mild biocompatible conditions, [59,[68][69][70] and have already been exploited to obtain molecular probes or therapeutic drug conjugates. ...
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... It brings various advantageous like moderate reaction conditions, high reaction yields, stereospecific reaction types, tolerance to varied functional groups and easily obliterable byproducts [151]. Especially, the effective coupling of functionalized nanofiller and polymer matrix via click reaction results in a remarkable distribution of the nanofillers in polymer matrix [152,153]. ...
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... The significance of the 'click' concept was originally foreseen to synthesize biologically active molecules. Eventually, it gained a remarkable recognition in macromolecular designing platform, which is affiliated with bulk-scale synthesis, lack of byproducts, and facile purification techniques [22][23][24][25] . Furthermore, in 2011, a group of renowned polymer chemists congregated to define criteria for the 'click' designation for a polymer-based reaction [26] . ...
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Controlled/living radical polymerization (CRP) has revolutionized and revitalized the field of synthetic polymer chemistry over the last twenty years as it is now possible to prepare a wide variety of previously inaccessible macromolecules under relatively mild conditions. Fundamentals of Controlled/Living Radical Polymerization provides an in-depth coverage of the essential chemical principles that enable and govern each of the CRP methods. The book starts with a brief historical overview of the major findings in polymer science which eventually led to the development of living ionic and living radical systems. It then goes on to introduce the main CRP techniques including their mechanistic understanding. The book also provides the information needed to select the appropriate reagents and conditions to conduct various CRP methods in a practical setting. Therefore, in addition to a newcomer gaining an appreciation for what has already been accomplished, the reader will be armed with the tools needed to begin independent research. Fundamentals of Controlled/Living Radical Polymerization provides essential insight into a rapidly growing field that goes beyond a simple literature review of the area. Written by leading experts in the field, the book is an indispensible resource for all researchers, instructors, and students in polymer chemistry.
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In the two decades since the introduction of the "click chemistry" concept, the toolbox of "click reactions" has continually expanded, enabling chemists, materials scientists, and biologists to rapidly and selectively build complexity for their applications of interest. Similarly, selective and efficient covalent bond breaking reactions have provided and will continue to provide transformative advances. Here, we review key examples and applications of efficient, selective covalent bond cleavage reactions, which we refer to herein as "clip reactions." The strategic application of clip reactions offers opportunities to tailor the compositions and structures of complex (bio)(macro)molecular systems with exquisite control. Working in concert, click chemistry and clip chemistry offer scientists and engineers powerful methods to address next-generation challenges across the chemical sciences.
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This study describes a one‐step Passerini and esterification reaction strategy for the first time at the macromolecular level in the literature. Polythioether (PT) including di‐tert‐butyl acetylenedicarboxylate (DTBADC) units is synthesized via a previously described rapid double thiol‐Michael addition polymerization method, followed by hydrolysis of tert‐butyl groups to produce dicarboxylic acid pendant polythioether (PH). PH is then utilized for postpolymerization modification via Passerini 3‐component reaction (Passerini‐ 3CR). Interestingly, it is found that on the course of Passerini‐3CR, the use of methanol (CH3OH) as a co‐solvent not only dissolves PH but also leads to the esterification reaction, which thereby further modifies the resultant polymer. This finding encourages the creation of a variety of ester functionality in the final polymer via Passerini‐3CR, by solely varying alcohols. The ratio of both ester and Passerini products in the modified polymers is monitored by 1H NMR analyses and a mechanistic aspect is also presented to product distribution. In addition, a monoacid containing polythioether (PMH) is prepared and used for the modification with Passerini‐3CR under the identical conditions described for PH, only Passerini product is obtained with no sign related to the ester product.
Article
Topologically unique polymers made of the cyclic chain such as tadpole and figure-eight polymers were synthesized via ring-expansion cationic polymerization (RECP) of vinyl ether with a functionalized-cyclic initiator, followed by...
Chapter
Thiol-X chemistries are already well established techniques, but it is only recently that they have been exploited for the functionalization and synthesis of polymers and other materials. As such, information on these techniques is scattered across the literature and Thiol-X Chemistries in Polymer and Materials Science is the first book to compile work specifically focussing on the application of thiol-based chemistries in materials design and synthesis. The book introduces the various thiol-X chemistries currently available and applications where they have been successfully used, including examples of 'click' processes, in polymerizations, polymer synthesis, and polymer modification. Short 'how to' sections within the chapters also provide general experimental techniques to employ the various chemistries described. Written by leading experts in the field, this book is a comprehensive resource for postgraduates, academics and industrial practitioners interested in polymer and materials applications.
Article
The use of ‘Click Reaction’ for Cu(I) catalyzed azide–alkyne cycloaddition (CuAAC) has emerged as one of the most powerful tools for the synthesis of library of organic molecules having a wide range of applications. The approach is highly stereoselective that involves the formation of 1,4–disubstituted 1,2,3–triazole derivatives by the combination of diverse structural entities in the presence of Cu(I) as catalyst. There are numerous synthetic Cu (I) complexes with different ligands bound in diverse molecular framework with potential to act as catalyst to stitch organic azide to alkyne producing 1,4-di-substituted products. This review emphasizes on those versatile Cu (I) complexes having tailoring capability similar to those available commercially.
Chapter
Thiol-X chemistries are already well established techniques, but it is only recently that they have been exploited for the functionalization and synthesis of polymers and other materials. As such, information on these techniques is scattered across the literature and Thiol-X Chemistries in Polymer and Materials Science is the first book to compile work specifically focussing on the application of thiol-based chemistries in materials design and synthesis. The book introduces the various thiol-X chemistries currently available and applications where they have been successfully used, including examples of 'click' processes, in polymerizations, polymer synthesis, and polymer modification. Short 'how to' sections within the chapters also provide general experimental techniques to employ the various chemistries described. Written by leading experts in the field, this book is a comprehensive resource for postgraduates, academics and industrial practitioners interested in polymer and materials applications.
Chapter
Thiol-X chemistries are already well established techniques, but it is only recently that they have been exploited for the functionalization and synthesis of polymers and other materials. As such, information on these techniques is scattered across the literature and Thiol-X Chemistries in Polymer and Materials Science is the first book to compile work specifically focussing on the application of thiol-based chemistries in materials design and synthesis. The book introduces the various thiol-X chemistries currently available and applications where they have been successfully used, including examples of 'click' processes, in polymerizations, polymer synthesis, and polymer modification. Short 'how to' sections within the chapters also provide general experimental techniques to employ the various chemistries described. Written by leading experts in the field, this book is a comprehensive resource for postgraduates, academics and industrial practitioners interested in polymer and materials applications.
Chapter
This article outlines the development of inorganic click (iClick) for metallopolymer synthesis. Included is a discussion relating traditional azide/alkyne cycloaddition reactions (CuAAC) and iClick, where the focus is on linking multiple metal ions to synthesize metallopolymers. Multiple synthetic approaches to metallopolymers are proposed to motivate the subject. An overview of the proposed iClick mechanism between a Au-acetylide and Au-azide is presented and compared to the currently accepted CuAAC version. Important milestone discoveries are discussed and include: linking metal ions through aurophilic bonds, the synthesis of heterobimetallic complexes via iClick, double iClick reactions at a single metal center and steric limitations, and the ultimate synthesis of the first metallopolymers using this methodology.
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With the help of amphiphilic homopolymers, this work explores the ‘click’ nature of the selenium-epoxy reaction, alkylation of the seleno-ethers as a means to prepare cationic polymers, and the antibacterial activity of polyselenonium salts.
Article
The inverse Electron Demand Diels-Alder (IEDDA) reaction between tetrazine and trans-cyclooctenol (TCO) is a fast and effective method employed to connect two or more molecules. In this study, an efficient and fast methodology based on tetrazine/trans-cyclooctene IEDDA reaction was developed for preparation of star-shaped block copolymers. Three-arm star polylactide-b-poly(ethylene glycol) (PLA-b-PEG) was chosen as a model system to show efficiency of the approach. First, three-arm PLAs with two different molecular masses were synthesized in a typical ring opening polymerization and functionalized with tetrazine end functionalities. while TCO end functionalized PEGs in two different molecular masses were perpared. Exact stoichiometric IEDDA click reaction between tetrazine moieties on three ends of the star polymer (s-3PLA-Tz) in the core and trans-cyclooctene (TCO) moieties of the periphery polymer (PEG-TCO) was performed in high click efficiency (up to 95.8%) in a short period (after 50–75 min). Ligation of PEG was confirmed by UV–vis, NMR and FT-IR spectroscopies, and size exclusion chromatography (SEC) and differential scanning calorimetry (DSC) analyses. In this way, various copolymers of desired architectures can be prepared in a short time and in high efficiency.
Article
The thiol–ene click reaction was applied to modify poly(isobutylene-co-isoprene) (IIR) by two different strategies using carboxylated thiols (mercaptanoic acids) with different alkyl spacer chain lengths. In the first approach, the direct radical-promoted addition of thiols across the 1,4-isoprene units proceeded with 80–90% conversion of the internal double bonds. An alternate method involving the conversion of sterically hindered 1,4-isoprene units to pendant double bonds through epoxidation and hydrolysis prior to the click reaction proceeded with 90–98% conversion of the alkene moieties. The carboxylated IIR derivatives were characterized by 1H NMR, FT-IR spectroscopy, and gel permeation chromatography analysis. Irrespective of the synthetic strategy used, the yields of the reactions decreased as the length of the alkyl spacer in the mercaptanoic acid increased. The outcomes of the reactions also depended on the amounts of solvent and free radical initiator used. Carboxylated butyl rubber derivatives were obtained by reacting the isoprene units in the isobutylene copolymer with alkylmercaptanoic acids comprising alkyl spacers of different lengths. The yield of the reactions varied from 80 to 90% for direct reaction of the copolymer containing 1,4-isoprene units, but increased to 90–98% if the 1,4-units were isomerized to terminal alkenes prior to the reactions.
Article
Glycolipids represent an attractive type of nonionic emulsifiers (surfactants) due to their abundant renewable resources and good biocompatibility. General preparation methods for glycolipids include enzymatic esterification or Lewis acid-catalyzed glycosylation. In this study, we report the synthesis of a novel series of triazolated alkyl glucolipids as emulsifiers by copper(I)-catalyzed click reactions, with side-chain length ranging from 4 to 10 carbons. The surface-active properties, foaming properties, emulsion properties, thermal stability as well as cytotoxicity of the synthesized compounds are evaluated to establish a comprehensive structure-property profiles, and results suggest the potential utility of medium sized glucolipids in, for example, pharmaceutical and food industries as they show superior performance than the tested commercial references.
Article
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In recent years, tremendous efforts have been dedicated to developing wood‐derived functional polymeric materials due to their distinctive properties, including environmental friendliness, renewability, and biodegradability. Thus, the uniqueness of the main components in wood (cellulose and lignin) has attracted enormous interest for both fundamental research and practical applications. Herein, the emerging field of wood‐derived functional polymeric materials fabricated by means of macromolecular engineering is reviewed, covering the basic structures and properties of the main components, the design principle to utilize these main components, and the resulting wood‐derived functional polymeric materials in terms of elastomers, hydrogels, aerogels, and nanoparticles. In detail, the natural features of wood components and their significant roles in the fabrication of materials are emphasized. Furthermore, the utilization of controlled/living polymerization, click chemistry, dynamic bonds chemistry, etc., for the modification is specifically discussed from the perspective of molecular design, together with their sequential assembly into different morphologies. The functionalities of wood‐derived polymeric materials are mainly focused on self‐healing and shape‐memory abilities, adsorption, conduction, etc. Finally, the main challenges of wood‐derived functional polymeric materials fabricated by macromolecular engineering are presented, as well as the potential solutions or directions to develop green and scalable wood‐derived functional polymeric materials. Wood components are considered as important feedstocks to fabricate functional materials. An insightful summary of recent wood‐derived functional polymeric materials is provided from the perspective of macromolecular engineering, including the structural characteristics of cellulose and lignin, molecular modification, and subsequent assembly behavior to generate distinctive functional materials.
Article
The base-catalyzed oxirane ring opening reaction with thiol nucleophiles is frequently employed for post-polymerization modification of polymeric glycidyl scaffolds. Due to various beneficial attributes, it is often referred to as a ‘click’ reaction. However, the tendency of the free thiol molecules to undergo oxidative dimerization through the formation of a disulfide bond under ambient conditions results in partial consumption of the sulfhydryl precursors. Therefore, an excess of the thiol precursors is typically used to counterbalance the side-reaction. This violates the equimolar stoichiometry conditions required for ‘click’ reactions in the context of polymer synthesis. Here, we show that commercially available disulfides can be used to generate the necessary thiolate nucleophiles in situ through the reduction of the SS-bond with sodium borohydride. Such activation strategy eliminates the sulfhydryl oxidation mechanism to disulfides and ensures that the post-synthesis functionalization of epoxy polymers can be performed under equimolar ‘click’ conditions.
Article
A new type of hybrid organosilicone polymer combining the coordination ability of triazole rings with the advantages of the highly branched topological structure of the flexible polysiloxane backbone was synthesized, characterized and exploited for the formation and stabilization of silver nanoparticles. In this study a series of functional 3-azidopropylethoxysiloxanes and poly-1,2,3-triazoleorganoethoxysiloxanes with controlled molecular architectures were synthesized and characterized for the first time using controlled condensation of the new AB2-type sodiumoxo-3-azidopropyldiethoxysilane monomer and the Copper(I)-catalyzed azide-alkyne cycloaddition “Click chemistry” process. The new 1,2,3-triazole-based hybrid polymers with a functional hyperbranched polyethoxysiloxane polymer backbone showed the ability to stabilize ultrasmall silver nanoparticles. The synthesized structures were characterized using ²⁹Si NMR, ¹H NMR, FTIR, Mass-spectrometry, and GPC. Polymer nanocomposites with the stabilized silver nanoparticles were characterized by transmission electron microscopy (TEM).
Article
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The bioinspired diblock copolymers poly(pentadecalactone)‐block‐poly(2‐(2‐hydroxyethoxy)benzoate) (PPDL‐block‐P2HEB) are synthesized from pentadecalactone and dihydro‐5H‐1,4‐benzodioxepin‐5‐one (2,3‐DHB). No transesterification between the blocks is observed. In a sequential approach, PPDL obtained by ring‐opening polymerization (ROP) is used to initiate 2,3‐DHB. Here, the molar mass Mn of the P2HEB block is limited. In a modular approach, end‐functionalized PPDL and P2HEB are obtained separately by ROP with functional initiators, and connected by 1,3‐dipolar Huisgen reaction (“click‐chemistry”). Block copolymer compositions from 85:15 mass percent to 28:72 mass percent (PPDL:P2HEB) are synthesized, with Mn of from about 30 000–50 000 g mol⁻¹. The structure of the block copolymer is confirmed by proton NMR, Fourier‐transform infrared spectroscopy, and gel permeation chromatography. Morphological studies by atomic force microscopy (AFM) further confirms the block copolymer structure, while quantitative nanomechanical AFM measurements reveal that the Derjaguin–Muller–Toporov moduli of the block copolymers range between 17.2 ± 1.8 and 62.3 ± 5.7 MPa, i.e., between the values of the parent P2HEB and PPDL homopolymers (7.6 ± 1.4 and 801 ± 42 MPa, respectively). Differential scanning calorimetry shows that the thermal properties of the homopolymers are retained by each of the copolymer blocks (melting temperature 90 °C, glass transition temperature 36 °C).
Article
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A bioinspired diblock copolymer is synthesized from pentadecalactone and 3‐hydroxy cinnamic acid. Poly(pentadecalactone) (PPDL) with a molar mass of up to 43 000 g mol⁻¹ is obtained by ring‐opening polymerization initiated by propargyl alcohol. Poly(3‐hydroxycinnamate) (P3HCA) is obtained by polycondensation and end‐functionalized with 3‐azido propanol. The two functionalized homopolymers are connected via 1,3‐dipolar Huisgen addition to yield the block copolymer PPDL‐triazole‐P3HCA. The structure of the block copolymer is confirmed by proton NMR, FTIR spectroscopy and GPC. By analyzing the morphology of polymer films made from the homopolymers, from a 1:1 homopolymer blend, and from the PPDL‐triazole‐P3HCA block copolymer, clearly distinct micro‐ and nanostructures are revealed. Quantitative nanomechanical measurements reveal that the block copolymer PPDL‐triazole‐P3HCA has a DMT modulus of 22.3 ± 2.7 MPa, which is lower than that of the PPDL homopolymer (801 ± 42 MPa), yet significantly higher than that of the P3HCA homopolymer (1.77 ± 0.63 MPa). Thermal analytics show that the melting point of PPDL‐triazole‐P3HCA is similar to PPDL (89–90 °C), while it has a glass transition temperature similar to P3HCA (123–124 °C). Thus, the semicrystalline, potentially degradable all‐polyester block copolymer PPDL‐triazole‐P3HCA combines the thermal properties of either homopolymer, and has an intermediate elastic modulus.
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A family of stereoregular poly(amide-triazole)s derived from D-galactose was obtained following several principles of Green Chemistry, namely bio-based starting materials, high yields, benign reaction conditions, energy efficiency, catalysis, atom economy, and chemical degradation. The monomer precursors, the α-azido-ω-N-alkynylamide derivatives, were prepared from D-galactose, which was oxidized to D-galactono-1,4-lactone and the secondary hydroxyl groups were protected as isopropylidene acetals. The AB-type azide-alkyne click polymerization led to poly(amide-triazole)s. The Cu(I)-catalyzed polymerization led regioselectively to 1,4-disubstituted triazole ring, and hence to a stereoregular polymer. In contrast, the thermal polymerization produced also 1,5-disubstituted triazole units. The stereoregular polymer underwent acid-promoted chemical degradation, and the degradation products were identified. Moreover, selective removal of the acid labile acetonide moieties led to a partially protected poly(amide-triazole). This polymer was further modified using the “grafting from” approach. Thus, the ROP of caprolactone initiated from the free hydroxyl groups of the polymer led to a linear poly(amide-triazole) grafted with short biodegradable polycaprolactone side-chains. On the other hand, complete HO-deprotection of the monomer gave, after click polymerization, the fully unprotected polymer. The protected poly(amide-triazole)s showed a higher thermal stability compared to the hydroxylated derivatives, which could undergo dehydration processes at lower temperatures. Similarly, the partially protected polymer gave a lower Tg value, in agreement with an increasing degree of structural disorder (non-stereoregular materials) and/or lower molecular weight.
Article
Polyesters that have a nitrile N-oxide function at the initiation end were prepared and applied to a catalyst-free click reaction for star polymer synthesis. They were obtained by an initial living ring-opening polymerization of lactide and lactones with an alcohol-bearing nitroalkane as the initiator, followed by conversion of the nitroalkane to a nitrile N-oxide function. The resulting polymer and block copolymer nitrile N-oxides showed very high reactivity toward a hexakis(alkenyl) core to give the corresponding star polymers via complete conversion.
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Using the Diels−Alder (DA) “click chemistry” strategy between anthracene and maleimide functional groups, two series of well-defined polystyrene-g-poly(ethylene glycol) (PS-g-PEG) and polystyrene-g-poly(methyl methacrylate) (PS-g-PMMA) copolymers were successfully prepared. The whole process was divided into two stages: (i) preparation of anthracene and maleimide functional polymers and (ii) the use of Diels−Alder reaction of these groups. First, random copolymers of styrene (S) and chloromethylstyrene (CMS) with various CMS contents were prepared by the nitroxide-mediated radical polymerization (NMP) process. Then, the choromethyl groups were converted to anthryl groups via the etherifaction with 9-anthracenemethanol. The other component of the click reaction, namely protected maleimide functional polymers, were prepared independently by the modification of commercially available poly(ethylene glycol) (PEG) and poly(methyl methacrylate) (PMMA) obtained by atom transfer radical polymerization (ATRP) using the corresponding functional initiator. Then, in the final stage PEG and PMMA prepolymers were deprotected by retro-Diels−Alder in situ reaction by heating at 110 °C in toluene. The recovered maleimide groups and added anthryl functional polystyrene undergo Diels−Alder reaction to form the respective (PS-g-PEG) and (PS-g-PMMA) copolymers. The graft copolymers and the intermediates were characterized in detail by using 1H NMR, GPC, UV, fluorescence, DSC, and AFM measurements.
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The present communication explores a novel avenue to glycopolymer-block-poly( vinyl acetate) polymers by a combination of reversible addition fragmentation chain transfer ( RAFT) chemistry and Huisgen 1,3-dipolar cycloaddition (i.e., so-called 'click' chemistry) under mild reaction conditions. Such block copolymers are - because of the strongly disparate reactivity of the two monomers - otherwise not obtainable. Poly( vinyl acetate) that has an azide end group (M-n 6800 g mol(-1), PDI 1.15) was treated with poly(6-O-methacryloyl mannose) (M-n 7600 g mol(-1), PDI 1.11) in the presence of 1,8-diaza[5,4,0] bicycloundec-7-ene and copper(I) iodide. The resulting poly( vinyl acetate)- block-poly( 6-O-methacryloyl mannose) had a number-average molecular weight of 15 400 g mol(-1) and a PDI of 1.48, which indicates that while the cycloaddition had occurred the resulting polymer distribution featured a considerable width. The resulting slightly amphiphilic block copolymer was subsequently investigated with regard to its self-assembly in aqueous solution. Dynamic light scattering studies indicated a hydrodynamic diameter of close to 200 nm. Transmission electron microscopy studies indicate the formation of rods as well as spheres with transitions between these two phases. However, the segregation between core and shell in the spheres is not pronounced; such behaviour is expected for weakly amphiphilic block copolymers.
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Hyperbranched copolymers of N-isopropylacrylamide (NIPAM) and styrene were prepared by reversible addition-fragmentation chain transfer ( RAFT) polymerization in the presence of a novel acryloyl trithiocarbonate, namely 1-[3-(2-methyl- 2-dodecylsulfanylthiocarbonylsulfanylpropionyloxy) propyl]-1H-[ 1,2,3] triazol-4-ylmethyl acrylate. By employing an example of 'click chemistry', we were able to prepare the vinyl RAFT chain transfer agent (CTA) by copper-catalyzed 1,3- dipolar cycloaddition of an azido-functionalized trithiocarbonate and propargyl acrylate. The resulting CTA facilitated the preparation of highly branched poly( N-isopropylacrylamide) ( PNIPAM) and polystyrene. Interestingly, the branched PNIPAM demonstrated a reduced lower critical solution temperature (LCST) of 25 degrees C as opposed to the conventional value of 32 degrees C expected for linear PNIPAM, an effect attributed to increased contribution of hydrophobic dodecyl trithiocarbonate end groups.
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Since its discovery in 2001, copper catalyzed azide–alkyne ‘click’ chemistry has been extensively used in polymer chemistry to modify polymeric materials and create advanced polymer structures by efficient coupling reactions. Surprisingly, the contribution of this Huisgen cycloaddition reaction to industrially important commodity polymers, prepared by step-growth polymerization, was not existing until recently. Nevertheless, since many decades academic and industrial research was focused on finding attractive synthetic pathways to introduce large contents of different reactive functional groups in several polymer classes such as polyesters and polyurethanes. Because of the high tolerance of azide–alkyne coupling reactions to a wide variety of functional groups and to extreme reaction conditions often used in step-growth polymerizations, the straightforward synthesis of alkyne-containing building blocks created an ideal platform to modify and broaden the physico-chemical properties of step-growth polymers by choosing readily available low and high molecular weight azide components. This feature article provides a comprehensive review covering the strategies toward ‘click’-functionalization of several classes of industrially important step-growth polymers.
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A functional monomer with a pendant azide moiety, 6-azidohexyl methacrylate (AHMA), was polymerized on the surface of silica nanoparticles via surface-initiated reversible addition−fragmentation chain transfer (RAFT) polymerization with considerable control over the molecular weight and molecular weight distribution. The kinetics of AHMA polymerization mediated by 4-cyanopentanoic acid dithiobenzoate (CPDB) anchored nanoparticles was investigated and compared with that of AHMA polymerization mediated by free CPDB under similar conditions. The subsequent postfunctionalizations of PAHMA-grafted nanoparticles were demonstrated by reacting with various functional alkynes via click reactions. Kinetic studies showed that the reaction of surface-grafted PAHMA with phenylacetylene surface-grafted PAHMA was much faster than that of free PAHMA with phenylacetylene, whereas in the case of high molecular weight alkynes surface-grafted PAHMA showed lower reaction rates as compared to free PAHMA.
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A novel reversible addition fragmentation technique chain transfer agent (RAFT CTA) was synthesized which permits the possibility of using RAFT polymerization and click chemistry together for surface modification. Using this RAFT CTA, the surface of silica nanoparticles was modified with polystyrene and polyacrylamide brushes via the “grafting to” approach. A click reaction was used to attach polymers onto the surface which produced relatively high grafting density. Both tethered polystyrene and polyacrylamide chains were found in the brush regime. The combination of ATRP and click chemistry was also explored for surface modification. To our knowledge, this is first report of RAFT polymerization and click chemistry together for surface modification.
Article
Toward the goal of assigning function to the tens of thousands of protein products encoded by eukaryotic and prokaryotic genomes, the field of proteomics requires new technologies that can functionally characterize proteins within the dynamic environment of the cell, where these biomolecules are subject to myriad posttranslational modifications and the actions of endogenous activators and inhibitors. Here, we report an advanced strategy for activity-based protein profiling (ABPP) that addresses this important need. We show that several enzymes can be labeled in an activity-based manner both in vitro and in vivo by an azido-sulfonate ester probe and that these labeling events can be detected in whole proteomes by copper-catalyzed ligation with a rhodamine-alkyne reagent. This click chemistry-based strategy for ABPP represents a unique and versatile method for functional proteome analysis.
Article
Block copolymers consisting of polyisobutylene (PIB) and either poly(methyl methacrylate) (PMMA) or polystyrene (PS) block segments were synthesized by a site transformation approach combining living cationic and reversible addition−fragmentation transfer (RAFT) polymerizations. The initial PIB block was synthesized via quasi-living cationic polymerization using the TMPCl/TiCl4 initiation system and subsequently converted into a hydroxyl-terminated PIB. Site transformation of the hydroxyl-terminated PIB into a macro-chain-transfer agent (PIB−CTA) was accomplished by N,N′-dicyclohexylcarbodiimide/dimethylaminopyridine-catalyzed esterification with 4-cyano-4-(dodecylsulfanylthiocarbonylsulfanyl)pentanoic acid. Structure of the PIB-CTA was confirmed by both 1H and 13C NMR spectroscopy. The PIB−CTA was then employed in a RAFT polymerization of either methyl methacrylate or styrene, resulting in PIB block copolymers with narrow polydispersity index and predetermined molecular weights confirmed by both 1H NMR and GPC.
Article
Polystyrenes, polyacrylates and poly(methyl methacrylate) prepared by atom transfer radical polymerization (ATRP) have predictable molecular weights, low polydispersities and well-defined halogen end groups. The halogen end groups have been substituted by other functionalities such as azides and amines. In order to predict the feasibility and selectivity of nucleophilic substitution reactions, the reactivities of the end groups of the different polymers were studied. First, model studies with benzyl halide (BzX), 1-phenylethyl halide (1-PEX), methyl 2-halopropionate (MXP), ethyl 2-bromoisobutyrate (EBiB) and 2-halopropionitrile (2-XPN) were performed. The models compounds were dissolved in DMF and after adding sodium azide (1.1 eq.), the reaction mixtures were stirred at 25°C. The relative magnitude of the rate constants for the reactions with the chlorinated substrates were found to be BzCl > MClP > 1-PECl ≈ 2-ClPN:22 > 6 > 1. Increased substitution at the carbon center decreased the rate of reaction, benzyl chloride reacted 22 times faster than 1-phenylethyl chloride. The brominated substrates reacted very fast. The rate constant of 1-PEBr, determined by competition experiments, was 4.5 times higher than the rate constant of benzyl chloride. Based on these results, the bromine end groups of different polymers were substituted under reaction conditions simular to those used for the model reactions. The end-functionalized polymers were characterized by H-NMR, IR and MALDI-TOFMS.
Article
Cycloaddition (CA) reactions have attracted recently strong interest not only for the preparation of linear polymers but also for the synthesis and modification of dendritic architectures. This review focuses mainly on the potential of various cycloaddition reactions in the field of dendrimers and especially hyperbranched polymers. The [4 + 2] Diels–Alder cycloaddition, [2 + 2 + 2] CA as well as 1,3-dipolar CA reactions including “click chemistry” will be addressed, and advantages of these reactions will be highlighted. High selectivity, thus high tolerance towards additional functionalities, high yields and often moderate to mild reaction conditions distinguish CA reactions from the often applied classical high-temperature polycondensation type reactions used mainly to synthesize hyperbranched polymers. Thus, besides the high potential in the synthesis and modification of perfectly branched dendrimers, cycloaddition reactions proved also very suited to prepare new types of hyperbranched structures.
Article
An ABCD 4-miktoarm star quaterpolymer with A = poly(ε-caprolactone) (PCL), B = poly(tert-butyl acrylate) (PtBA), C = polystyrene (PS) and D = poly(methyl methacrylate) (PMMA) arms was prepared using the Diels–Alder reaction strategy. Firstly, PCL with anthracene (PCL-Anth) and PtBA with furan-protected maleimide (PtBA-MI) end-functionalities were synthesized separately via ring-opening polymerization of ε-CL and atom transfer radical polymerization of tBA, respectively. These homo-polymers were linked via the Diels–Alder click reaction in toluene at 100°C in order to give PCL-b-PtBA co-polymer. Next, this block co-polymer is utilized successively as macroinitiator in nitroxide-mediated radical polymerization of styrene and in free radical photo-polymerization of MMA in order to achieve the PCL-PtBA-PS-PMMA 4-miktoarm star quaterpolymer.
Article
Multisegmented block copolymers were prepared by the step-growth click coupling of well-defined block copolymers synthesized by atom transfer radical polymerization (ATRP). alpha,omega-Diazido-terminated polystyrene-blockpoly( ethylene oxide)-block-polystyrene was coupled with propargyl ether in N,N-dimethylformamide in the presence of a CuBr/N,N,N',N '',N ''-pentamethyldiethylenetriamine catalyst. The preparation of multisegmented block copolymers was also demonstrated by the click coupling of propargyl ether with another diazido-terminated triblock copolymer, poly(n-butyl acrylate)-block-poly(methyl methacrylate)-block-poly( n-butyl acrylate), and a diazido-terminated pentablock copolymer, polystyrene-block-poly(n-butyl acrylate)-block-poly( methyl methacrylate)-block-poly( n-butyl acrylate)-block-polystyrene. The formation of a product of higher molecular weight and broader molecular weight distribution was verified by triple-detection size exclusion chromatography, which revealed that typically five to seven block copolymers were linked together during the click reaction. Differential scanning calorimetry and dynamic mechanical analysis revealed that the amphiphilic block copolymer behaves as a viscoelastic fluid, while its corresponding multiblock copolymer is an elastic material. The multisegmented block copolymers with partially miscible segments exhibit higher glass transition temperatures than their precursors.
Article
The macromolecules magazine has announced the inaugural 'virtual issue' having a set of thematically related, recently published papers collected in a web-only edition of the journal. These papers may also be found directly from the Macromolecules home page http://pubs.acs.org/page/mamobx/vi/1. These papers are freely accessible, even for readers without a subscription, until the next virtual issue takes its place. The magazine is aimed to provide access to new exciting-recent science in Macromolecules, to draw attention to various specific topics that these related papers address, and to serve as a valuable resource to the community. This issue contains selected topic from the modern polymer synthesis and applications along with the use 'click chemistry'. The magazine also encourages suggestions for future topics and for individuals to organize virtual issues as guest editors.
Article
In this paper, the combination of atom transfer radical polymerization (ATRP) of 1-ethoxyethyl acrylate (EEA) and the copper(I) catalyzed “click” 1,3-dipolar cycloaddition reaction of azides and terminal alkynes was evaluated as a method to synthesize diverse amphiphilic copolymer structures. Using the 1-ethoxyethyl protecting group strategy, the application field was broadened with the synthesis of complex polymer structures containing poly(acrylic acid) (PAA) segments. A modular approach has been used: polymers with alkyne functionalities as well as azide functionalities have been synthesized. These polymers were subsequently “clicked” together to yield block copolymers. Furthermore, graft copolymers were synthesized by grafting alkyne-containing polymers onto a polymer backbone with multiple azide functions using the combination of ATRP and “click” reactions.
Article
Efficient syntheses of tripodal thioethers have been achieved by ionic thiol-ene reactions of 1,3,5-triacryloylhexahydro-1,3,5-triazine (TAT) with a variety of commercially available thiols. The reactions are complete within minutes and give the products in high yields (63−96%) and high purity without a complex workup. The thiol-ene reactions tolerate a wide range of functionality, including hydroxy, amino, carboxylate, and trimethoxylsilyl groups. The amino acid cysteine is also an excellent substrate for this reaction.
Article
We report a simple synthetic protocol for the 1,3-dipolar cycloaddition of azides with electron-deficient alkynes. Alkyne with at least one neighboring electron-withdrawing group proceeds with the cycloaddition successfully without any catalysts at room temperature in water. Under this simple condition, we evaluated a series of small molecule model reactions and then coupled an azido-DNA molecule with electron-deficient alkynes for the formation of [1,2,3]-triazole heterocycle, providing a potential method for introducing functional groups to DNA under biological conditions.
Article
A study was conducted to provide an access route to diene-functionalized polymers through atom transfer radical polymerization (ATRP) and their utilization in the reversible addition-fragmentation chain transfer (RAFT)-hetero-Diels-Alder (HDA) protocol, which opened the possibilities of controlled radical polymerization (CRP) techniques to access complex architectures. 1,8-Diazabicyclo[5.4.0]undec-7-ene, trans,trans-2,4-hexadiene-1-ol, succinic anhydride, N,N-iisopropylethylamine, zinc chloride, and 1,10-azobis(cyclohexanecarbonitrile) were used for the study as received. Preparative GPC analysis was also carried out with CHCl3 as the solvent at a flow rate of 10 mL min-1 at room temperature. It was observed that the bromine end groups from the ATRP mechanism provided a synthetic handle for post-polymerization modifications. It was concluded that the RAFT-HDA conjugation approach was suitable for the tailor-made synthesis of complex macromolecular architectures.
Article
The preparation of 3-miktoarm star terpolymers using nitroxide mediated radical polymerization (NMP), ring opening polymerization (ROP), and click reaction [3 + 2] are carried out by applying two types of one-pot technique. In the first one-pot technique, NMP of styrene (St), ROP of ε-caprolactone (ε-CL), and [3 + 2] click reaction (between azide end-functionalized poly(ethylene glycol) (PEG-N3)/or azide end-functionalized poly(methyl methacrylate) (PMMA-N3) and alkyne) are carried out in the presence of 2-(hydroxymethyl)-2-methyl-3-oxo-3-(2-phenyl-2-(2,2,6,6-tetramethylpiperidin-1-yloxy)ethoxy) propyl pent-4-ynoate, 2, as an initiator for 48 h at 125 °C (one-pot/one-step). As a second technique, NMP of St and ROP of ε-CL were conducted using 2 as an initiator for 20 h at 125 °C, and subsequently PEG-N3 or azide end-functionalized poly(tert-butyl acrylate (PtBA-N3) was added to the polymerization mixture, followed by a click reaction [3 + 2] for 24 h at room temperature (one-pot/two-step). The 3-miktoarm star terpolymers, PEG-poly(ε-caprolactone)(PCL)-PS, PtBA-PCL-PS and PMMA-PCL-PS, were recovered by a simple precipitation in methanol without further purification. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3588–3598, 2007
Article
An elegant route to aromatic hydrocarbon dendrimers, such as 1 with pentaphenylbenzene units, and to extremely large polybenzenoid hydrocarbons is based on Diels–Alder cycloadditions of 3,4-bis-[4-(triisopropylsilylethynyl)phenyl]-2, 5-diphenylcyclopenta-2,4-dienone and aromatic oligoethynyl compounds such as 3,3′,5,5′-tetraethynylbiphenyl. The type of linkage and the high packing density of the benzene rings facilitate the cyclodehydrogenation of appropriate dendrimeric subunits to yield planar disks.
Article
Click chemistry is considered as one of the most rapidly growing areas of research in materials synthesis. Click chemistry can be applied to highly efficient dendritic materials synthesis requiring minimal purification and in the development of novel adhesives for copper surfaces. Click chemistry allows particular new materials to be prepared and opens up whole new avenues for materials to be prepared more efficiently. It also allows existing materials classes to be prepared with unprecedented efficiency and versatility opening up an array of new structures. It provides a valuable alternative to living polymerization methods such as anionic, ring opening, living radical systems where blocks are made through sequential polymerization of monomers rather than through coupling of performed blocks. It is expected that the efficiency and user friendliness of click reactions will continue to allow new functional materials with important commercial applications to be prepared.
Article
A facile and efficient synthetic approach to tripodal star-shaped oligomers is described. Several generations of hydroxyl-terminated tripodal star-shaped oligomers were prepared in high yield from 1,3,5-triacryloylhexahydro-1,3,5-triazine (TAT) as a core by alternating amine-catalyzed thiol-ene and acrylate esterification reactions. The compounds were fully characterized by 1D and 2D NMR spectroscopy, ESI-MS, and elemental analysis. The combination of thioether groups and hydrogen bonding moieties suggests that these products can be used as metal chelating ligands.
Article
The inverse star block copolymer, (poly(ε-caprolactone)-b-polystyrene)2-core-(poly(ε-caprolactone)-b-polystyrene)2, [(PCL-PS)2-core-(PCL-PS)2] has been successfully prepared by combination of atom transfer radical polymerization (ATRP), ring opening polymerization (ROP), and “Click Chemistry.” The synthesis includes the following five steps: (1) synthesis of a heterofunctional initiator with two ATRP initiating groups and two hydroxyl groups; (2) formation of (Br-PS)2-core-(OH)2 via ATRP of styrene; (3) preparation of the (PCL-PS)2-core-(OH)2 through “click” reaction of the α-propargyl, ω-acetyl terminated PCL with (N3-PS)2-core-(OH)2 which was prepared by transformation of the terminal bromine groups in (Br-PS)2-core-(OH)2 into azide groups; (4) the ROP of CL using (PCL-PS)2-core-(OH)2 as macroinitiator to form (PCL-PS)2-core-(PCL-OH)2; and (5) preparation of the (PCL-PS)2-core-(PCL-PS)2 through the ATRP of styrene using (PCL-PS)2-core-(PCL-Br)2 as macroinitiator which was prepared by reaction of the terminal hydroxyl groups at the end of the PCL chains with 2-bromoisobutyryl bromide. The characterization data support structures of the inverse star block copolymer and the intermediates. The differential scanning calorimeter results and polarized optical microscope observation showed that the intricate structure of the inverse star block copolymer greatly restricted the movement of the PS segments and PCL segments, resulted in the increase of the glass transition temperature of PS segments and the decrease of crystallization ability of PCL segments. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7757–7772, 2008
Article
Click chemistry has been used to prepare a range of novel polymers with pendant carboxylic acid side groups. Four azido carboxylic acids, either mono- or difunctional and aliphatic or aromatic, have been prepared and thoroughly characterized. Extensive model reactions with 1-ethyl-4-hydroxybenzene, the simplest model for poly(4-hydroxystyrene), and the four azido carboxylic acids have been conducted to establish the proper reaction conditions and provide an analytical frame for the corresponding polymers. Poly(4-hydroxystyrene) moieties in three different polymers—poly(4-hydroxystyrene), poly(4-hydroxystyrene-co-methyl methacrylate), and poly(4-hydroxystyrene-b-styrene)—have been quantitatively transformed into oxypropynes by the use of either Williamson or Mitsunobu strategies and subsequently reacted with the azido carboxylic acids. Detailed differential scanning calorimetry investigations of all the polymers in general exhibit [when poly(4-hydroxystyrene) is a substantial part] significant changes in the glass-transition temperature from the polar poly(4-hydroxystyrene) (120–130 °C) to the much less polar alkyne polymers (46–60 °C). A direct correlation between the nature of the pendant groups in the derivatized polymers and the glass-transition temperature has emerged: the aromatic carboxylic acids give high glass-transition temperatures (90–120 °C), and the aliphatic carboxylic acids give lower glass-transition temperatures (50–65 °C). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:6360–6377, 2006
Article
The 1,3-Dipolar cycloadditions of terminal diynes with aromatic diazides are used for the generation of nanostructured organic semiconductors by heated atomic force microscope (AFM) cantilever tips. The fabrication is done by nanoscale thermal processing of annealed diazide/dialkyne thin films. The cantilever tip was brought into contact with the film with a load force of ~100 nN and heated. Precision calibration of the cantilever was possible and the tip temperature was near 225 °C. Conjugated polymer form from azide and alkyne precursors under thermal and Cu-catalyzed conditions. It is possible to write crisp nanoscale features into mixed diazide-diyne films after preannealing, using a heated cantilever. The absence of thickness and ripping makes this materials particularly attractive as novel organic semiconductors that can be easily thermally structured.
Article
The fixation of ligands onto molecules, surfaces and materials by use of reactions using a simple and unified chemistry is among the everlasting desires of chemists. Besides the general insensitivity with respect to the chemical structures of the ligand, the completeness of the reaction as well as the insensitivity from external reaction parameters (i.e.: solvents, ambient temperature) is wished. The copper(I)-catalysed azide/alkyne “click”-reaction (also termed Sharpless “click”-reaction, a variation of the Huisgen 1,3-dipolar cycloaddition reaction between terminal acetylenes and azides) is a recent re-discovery of a reaction fulfilling these requirements. Extremely high yields (usually above 95%) are combined with a high tolerance of functional groups and reactions running at moderate temperatures (25°C - 70 °C). The present review assembles recent literature for applications of these reactions in the field of material science, in particular on surfaces, polymers, and for the ligation of ligands to larger biomolecules, including own publications in this field. Since this is an extremely fast developing area, this review offers important knowledge to the interested reader. A number of >64 references are included.
Article
The surface functionalization of macroporous polyHIPE (pHIPE) was achieved by Huisgen-type 'click' chemistry. In the first step a 600-800 nm thick layer of poly(glycidyl methacrylate) (pGMA) was grafted from the pHIPE surface by atom transfer radical polymerization (ATRP). Near quantitative azidation of the pGMA layer was achieved by the ring-opening reaction of the epoxide groups with sodium azide. The influence of the reaction conditions on the uniformity of the 'click' reaction on the three-dimensional macroporous materials was shown in model reactions with propargyl alcohol. Under optimized conditions, azide conversions of around 80% were estimated from IR-spectra. Visualization of the homogeneous functionalization was achieved by the attachment of a fluorescent molecule. Moreover, the first proof of the versatility for biofunctionalization of pHIPE by this method was provided by the attachment of several protected amino acids. The hydrolytic stability of the triazole ring allows for the successful deprotection of the amino acids on the pHIPE.
Article
The application of thiol−ene chemistry to the synthesis of new carbosilane−thioether dendrimers is presented in this work. The dendrimers are prepared in a divergent fashion starting with tetravinylsilane as a core, followed by a succession of alternating thiol−ene and Grignard reactions. Vinyl-terminated dendrimers up to the fifth generation were isolated in excellent yields (78−94%). Products were characterized by multinuclear NMR spectroscopy, dynamic light scattering, gel permeation chromatography, and MALDI-TOF mass spectrometry.
Article
Various commercially available thiols react photochemically with tetravinylsilane to give the corresponding tetrasubstituted thioether compounds. The reactions are conducted in air using typical borosilicate glassware. Yields range from 64 to 100%, and purification steps, if necessary, involve simple precipitation or extraction steps. Thiol addition occurs predominantly to give the anti-Markovnikov product; amounts of Markovnikov addition range from 1 to 5%.
Article
We describe a straightforward approach to synthesize polymers with end-groups that bind site-specifically to two different proteins. Telechelic biotin−maleimide poly(N-isopropylacrylamide) (pNIPAAm) was synthesized for the formation of streptavidin (SAv)−bovine serum albumin (BSA) polymer conjugates. Reversible addition−fragmentation chain transfer (RAFT) polymerization of NIPAAm was conducted in the presence of biotinylated chain transfer agents (CTAs) with either ester or amide linkages, and the resultant α-biotinylated pNIPAAms were formed with low polydispersity indices (PDI ≤ 1.09). UV−vis analysis of the trithiocarbonate chain-ends indicated 88% or greater retention of the group. A maleimide was introduced to the ω chain-end via a radical cross-coupling reaction with a functionalized azo-initiator. The polymer structures were characterized by 1H NMR spectroscopy and gel permeation chromatography (GPC). The resultant biotin−maleimide heterotelechelic polymer was used to form a SAv−BSA heterodimer conjugate. Bioconjugate formation was confirmed by gel electrophoresis.
Article
A series of alkene-functional polymers were synthesized by controlled polymerization techniques in order to investigate and compare the efficiency and orthogonality of both photochemically and thermally initiated thiol−ene click coupling reactions. The copolymers were designed to have single or multiple alkene-functional groups along the backbone, and to evaluate the robustness of these procedures, functionalization reactions with a library of mercaptans were studied. In comparing the photoinitiated reaction to its thermal counterpart, the thiol−ene photocoupling was found to proceed with higher efficiency, require shorter reaction times for complete conversion, and displayed a higher tolerance to various backbones and functional groups. To examine the orthogonality of the thiol−ene click reaction, an asymmetric telechelic polymer based on PS was designed with alkene functionality at one end and an azide at the other. The thermally initiated thiol−ene coupling was found to be completely orthogonal with the traditional azide/alkyne click reaction allowing the individual chain ends to be quantitatively functionalized without the need for protection/deprotection strategies. From these studies, the demonstrated efficiency and orthogonality of thiol−ene chemistry shows it to be a practical addition to the family of click reactions that are suitable for polymer functionalization.
Article
Reversible addition-fragmentation chain transfer (RAFT) polymerization in the presence of a compound capable of both reversible chain transfer through a thiocarbonylthio moiety and propagation via a vinyl group led to highly branched copolymers by a method analogous to self-condensing vinyl copolymerization. An acryloyl trithiocarbonate prepared by copper-catalyzed azide-alkyne cycloaddition was copolymerized with N-isopropylacrylamide (NIPAM) in ratios selected to tune the distribution and length of branches in the resulting thermoresponsive polymers. The degree of branching increased with chain transfer agent (CTA) concentration, as proven by NMR spectroscopy, size exclusion chromatography, and viscometry. Retention of the thiocarbonylthio compound during the polymerization was evidenced by successful chain extension of a branched N-isopropylacrylamide (PNIPAM) macroCTA by RAFT polymerization of N,N-dimethylacrylamide. The branched polymers led to reduced lower critical solution temperatures as compared to linear PNIPAM, an effect attributed primarily to an increased contribution of hydrophobic end groups. End group cleavage by radical-induced reduction resulted in an increased transition temperature more similar to that expected for linear PNIPAM.
Article
The noncatalyzed cycloaddition of azides with electron-poor olefins was investigated in conditions mimicking those of living radical polymerization. The pathway of this reaction was investigated, and model reactions were designed to study this reaction with various types of monomers (N-isopropylacrylamide, dimethylacrylamide, methyl acrylate, methyl methacrylate, and styrene). We found that the azide undergoes 1,3-cycloaddition with the double bond of these monomers, in the absence of catalyst, at high temperatures (60 °C) and for long reaction times. This side reaction can be of dramatic significance as it impairs the orthogonality of copper-catalyzed azide−alkyne cycloaddition (“click chemistry”); short polymerization time and low temperatures should be targeted to limit these side reactions.
Article
A study was conducted to investigate an alternative cyclization approach for efficient preparation of cyclic poly(methylacrylate)-block-poly(styrene) by combining atom transfer radical polymerization (ATRP) and click cyclization. A team of researchers demonstrated that the function group tolerance, facile end-group modification, and controlled polymerizations offered by atom transfer radical polymerization can be paired with the Huisgen 1,3-dipolar cycloaddition click coupling process, to generate high-purity cyclic polystyrene, without excess quantities of solvent, or fractionation methods, to purify the product. It was observed that the procedure can provide an efficient route, to prepare a wide range of homopolymers, due to the function group tolerance of both ATRP and the click reaction.
Article
Polytetrahydrofuran (PTHF)/clay nanocomposites were prepared by two routes: in situ cationic ring opening polymerization (CROP) and a method involving “click” chemistry. In the first method, PTHF chains were grown from the surface of the organo-modified montmorillonite clay by CROP of tetrahydrofuran (THF) through the hydroxyl functions of the clay by using trifluoromethanesulfonic anhydride, in the presence of 2,6-di-tert-butylpyridine as proton trap and dichloromethane as solvent. The polymerizations were affected by the clay content ratios. The living characteristics of the polymerization were demonstrated by the semilogarithmic first order kinetic plot. In the second method, CROP of THF has been performed independently to produce alkyne-functionalized PTHF and the obtained polymers were subsequently anchored to azide-modified clay layers by a “click” reaction. The exfoliated polymer/clay nanocomposites obtained by both methods were characterized and compared by X-ray diffraction spectroscopy, thermogravimetric analysis, and transmission electron microscopy. Compared to the virgin polymer, the nanocomposites exhibited improved thermal stabilities regardless of the preparation method. However, the nanocomposites prepared by the “click” chemistry approach appeared to be thermally more stable than those prepared by in situ polymerization. Moreover, the “click” chemistry method also provided better exfoliation.
Article
A set of different alkyne containing diblock copolymers based on 4-hydroxystyrene was synthesized by nitroxide mediated radical polymerization (NMRP), all with excellent control over the molecular composition and narrow molar mass distribution. The diblock copolymers consist of labile protected 4-hydroxystyrene motifs in one block and bear alkyne functionalities in each repeating unit of the second block, thus making the materials candidates for polymer analogous modification reactions by a very efficient cycloaddition reaction. The use of 4-(trimethylsilylpropargyloxy)styrene as monomer proved highly advantageous compared to 4-(trimethylsilylethynyl) styrene, first because high control was kept in the NMRP process and second because there was higher accessibility in the postmodification reaction. In fact, quantitative postmodification through Cu(I)-catalyzed cycloaddition reaction of the pending propargyloxy groups with bulky adamantane azide of the diblock copolymers was achieved, yielding microphase-separated materials with a rigid block.
Article
Click chemistry is used to obtain new conductive polymer films based on poly(3,4-ethylenedioxythiophene) (PEDOT) from a new azide functional monomer. Postpolymerization, 1,3-dipolar cycloadditions in DMF, using a catalyst system of CuSO4 and sodium ascorbate, and different alkynes are performed to functionalize films of PEDOT-N3 and copolymers prepared from EDOT-N3 and 3,4-ethylenedioxythiophene (EDOT). This approach enables new functionalities on PEDOT that could otherwise not withstand the polymerization conditions. Reactions on the thin polymer films have been optimized using an alkynated fluorophore, with reaction times of 20 h. The applicability of the method is illustrated by coupling of two other alkynes: a short chain fluorocarbon and a MPEG 5000 to the conductive polymer; this alters the advancing water contact angle of the surface by +20° and −20°/−25°, respectively. The targeted chemical surface modifications have been verified by X-ray photoelectron spectroscopy analysis.
Article
Macrophotoinitiators containing thioxanthone (TX) moieties as side chains were synthesized by using “double click chemistry” strategy; combining in-situ 1,3-dipolar azide−alkyne [3 + 2] and thermoreversible Diels–Alder (DA) [4 + 2] cycloaddition reactions. For this purpose, thioxanthone−anthracene (TX−A), N-propargyl-7-oxynorbornene (PON), and polystyrene (PS) with side-chain azide moieties (PS−N3) were reacted in N,N-dimethylformamide (DMF) for 36 h at 120 °C. In this process, PON acted as a “click linker” since it contains both protected maleimide and alkyne functional groups suitable for 1,3-dipolar azide−alkyne and Diels−Alder click reactions, respectively. This way, the aromacity of the central phenyl unit of the anthracene moiety present in TX−A was transformed into TX chromophoric groups. The resulting polymers possess absorption characteristics similar to the parent TX. Their capabilities to act as photoinitiator for the polymerization of mono- and multifunctional monomers, namely methyl methacrylate (MMA) and 1,1,1-tris(hydroxymethyl)propane triacrylate (TPTA) were also examined.
Article
Poly(norbornene)-based random copolymers possessing either azide, aldehyde, or ketone functionalities on each repeating unit were synthesized using ring-opening metathesis polymerization. The orthogonal functionalization of the resulting copolymers using 1,3-dipolar cycloadditions and hydrazone formations was investigated. While the azide- and aldehyde-containing copolymers were insoluble in organic solvents, the azide- and ketone-functionalized copolymers were fully soluble in common solvents such as CH2Cl2, THF, and DMF and can be quantitatively functionalized with a library of small organic and biological molecules in a stepwise fashion. The orthogonal functionalization of the ketone/azide copolymers was characterized by NMR and IR spectroscopies and gel-permeation chromatography. A one-pot dual functionalization strategy is also presented that allows for the quantitative dual functionalization of copolymers. This one-pot strategy introduced herein for the preparation of multifunctional macromolecules provides a modular platform for potential applications ranging from electronic materials to polymer-mediated drug delivery.
Article
We report on the preparation of well-defined cyclic poly(N-isopropylacrylamide) (cyclic-PNIPAM) via click chemistry and its unique thermal phase transition behavior as compared to the linear counterpart. α-Alkyne-ω-azido heterodifunctional PNIPAM precursor (linear-PNIPAM-N3) was prepared by atom transfer radical polymerization (ATRP) of N-isopropylacrylamide in 2-propanol using propargyl 2-chloropropionate as the initiator, followed by reacting with NaN3 to transform the terminal chloride into azide group. The subsequent end-to-end intramolecular coupling reaction under high dilution and “click” conditions leads to efficient preparation of narrow-disperse cyclic-PNIPAM. Gel permeation chromatography (GPC), 1H NMR, Fourier transform infrared (FT-IR), and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry all confirmed the complete transformation of linear-PNIPAM-N3 to cyclic-PNIPAM. The thermal phase transition behavior of cyclic-PNIPAM was investigated by temperature-dependent turbidity measurements and micro-differential scanning calorimetry (micro-DSC) and compared to that of linear-PNIPAM-N3 with the same molecular weight. The former possesses lower critical solution temperatures (LCSTs), more prominent concentration dependences of LCST values and cloud points (CPs), broader thermal phase transition range, and prominently lower enthalpy changes (ΔH). The above differences in thermal phase transition behaviors between cyclic- and linear-PNIPAM should be due to the absence of chain ends and stringent restrictions on backbone conformations in the former.
Article
The cyclic PNIPAMs were synthesized by ring closure of α,Σ- heterodifunctional telechelic PNIPAM precursors. The synthesis of PNIPAM was accomplished in three steps, first telechelic PNIPAMs were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAM) using an azide containing trithiocarbonate, 2-(2-azidoethoxy)ethyl 2-( 1-isobutyl)sulfanylthiocarbonylsulfanyl-2-methyl propionate) (AIP) as chain transfer agent. A low initiator/AIP (1:10) ratio was selected in order to ensure high terminal functionality and narrow molecular weight distribution. The structure of the 1-PNIPAM samples was confirmed by analysis of their 1H NMR spectra and the aqueous solutions of c-PNIPAM and its linear precursors were analyzed by high sensitivity differential scanning microcalorimetry and turbidity.
Article
The radical addition of mercaptans (RSH) onto poly[2-(3-butenyl)-2-oxazoline], which is available through a living/controlled cationic isomerization polymerization, can proceed smoothly in the absence of side reactions, exhibiting the characteristics of a click reaction. The “thio-click” reaction can be performed under feasible ([RSH]/[CC] 1.2−1.5, no transition metal additives) and mild conditions (generation of radicals with UV light at room temperature) and goes to completion within a day. Hydrophobic fluoropolymers can be prepared in the same way as water-soluble (co-)polymers or glycopolymers, starting from readily available materials.
Article
Aminooxy α- and α,ω-end-functionalized polystyrene were synthesized via atom transfer radical polymerization (ATRP) and atom transfer radical (ATR) coupling. A 1-bromoethylphenyl initiator possessing an N-hydroxyphthalimide group was used for copper-mediated ATRP of styrene. The polymerization kinetics indicated good control with high initiator efficiency, and the resulting polymers had polydispersity indices (PDIs) as low as 1.12. N-Hydroxyphthalimide−polystyrene was then dimerized using Cu(0)-mediated ATR coupling, and GPC results indicated high coupling efficiency. Hydrazine deprotection of both the α and α,ω-end-functionalized polystyrene to the aminooxy groups was confirmed by 1H NMR spectroscopy. End-group reactivity was verified by reaction with 4-bromobenzaldehyde to form the oxime linkages.
Article
Chemoselective oxime formation between aminooxy end-functional polymers and levulinyl-modified proteins is an attractive method to prepare well-defined bioconjugates. We demonstrate the synthesis of Boc-protected aminooxy initiators for atom transfer radical polymerization (ATRP) of acrylamide and methacrylate monomers. Copper-mediated ATRP of N-isopropylacrylamide (NIPAAm), 2-hydroxyethyl methacrylate (HEMA), and poly(ethylene glycol) methacrylate (PEGMA) resulted in polymers with polydispersity indices (PDIs) as low as 1.11, 1.18, and 1.24, respectively. Kinetic analysis indicated that ATRP of HEMA was well-controlled. The polymer end groups of polyNIPAAm were deprotected with trifluoroacetic acid, exposing α-aminooxy moieties. Complete removal of the Boc groups was confirmed by 1H NMR, and the ability to form oxime bonds was verified by conjugation to aldehyde fluorescent nanospheres. Chemospecific reaction with Nε-levulinyl lysine-modified bovine serum albumin (BSA) to form “smart” polymer conjugates was demonstrated.
Article
The use of copper(I)-catalyzed “click” reactions of azides and alkynes for covalent layer-by-layer grafting on polyethylene is described. Water-soluble poly(N-alkylacrylamide) copolymers that contain pendant azide or alkyne groups that can be thermally separated from aqueous solutions were used to alternately “click” together azide and alkyne polymers via 1,2,3-triazole formation onto a prefunctionalized alkyne-containing surface. The layer-by-layer self-assembly process proceeds under ambient conditions and was followed by ATR-IR spectroscopy using control reactions to show that azide groups and copper catalysis are required for the assembly process. Post-graft functionalization of the hyperbranched assembly is used to demonstrate that the functional interfaces so formed can be further derivatized for other functions.
Article
Heating mixtures of bis(aroylacetylene)s (5/6/9) and diazides (7/8) in polar solvents such as DMF/toluene at a moderate temperature of 100 °C readily affects their 1,3-dipolar polycycloadditions, producing poly(aroyltriazole)s (PATAs; PI−PXII) with high molecular weights (Mw up to 26 700) and regioregularities (F1,4 up to 92%) in high yields (up to 98%). The metal-free click polymerizations propagate smoothly in an open atmosphere without protection from oxygen and moisture. Through model reaction study and semiempirical calculation, the polymerization mechanism is proposed and discussed. Molecular structures of the PATAs are characterized spectroscopically. All the polymers are soluble in common organic solvents and are thermally stable, losing little of their weights when heated to 380 °C. The PATAs containing triphenylamine units emit visible light and show unique solvatochromism. The PATAs are nonlinear optically active, exhibiting large two-photon absorption cross sections due to the intramolecular charge transfer between their electron-donating triphenylamine and electron-accepting aroyltriazole units.
Article
We report on the synthesis of telechelic poly(N-isopropylacrylamides) (PNIPAM) via nitroxide-mediated controlled polymerization, putting a focus on the introduction of defined end group moieties into telechelic poly(N-isopropylacrylamide) and poly(n-butyl acrylates). Various functional groups, linked to the central nitroxide-initiator via a triazole moiety resulting from an azide/alkyne-“click” reaction were probed with N-isopropylacrylamide and n-butyl acrylate as monomers in terms of efficiency and livingness. Functional groups on the initiator include a 1,2-dihydroxyalkyl moiety and a barbituric acid moiety as well as a phenyl moiety. Those initiators with a 1,2,3-1H-triazole moiety directly bound to the initiator group displayed a poor initiating quality toward N-isopropylacrylamide, whereas an ester bridge as linker between the initiator molecule and the functional group showed highly living character with respect to N-isopropylacrylamide and n-butyl acrylate as probed by kinetic experiments. Effects based upon internal hydrogen-bonding effects are made responsible rather than purely stereoelectronic effects, as proven by force-field calculations. MALDI time-of-flight mass spectrometry was used to prove the incorporation of the respective end groups into the telechelic PNIPAM polymers. Finally, the versatility of the method was demonstrated via a “grafting-from” approach of PNIPAM from magnetic iron oxide nanoparticles via a surface-bound initiator, resulting in an excellent control of molecular weight and thus thickness of the polymeric shell around the magnetic nanoparticles.
Article
A tadpole shaped poly(ε-caprolactone) (PCL; Mn = 24 500) was made amphiphilic by grafting the two PCL tails with PEO. In the first step, a macrocyclic PCL was synthesized by ring-opening polymerization of ε-caprolactone (εCL) initiated by a cyclic tin(IV) dialkoxide and stabilized by local intramolecular photo-cross-linking. In the second step, the polymerization of a mixture of εCL and α-chloro-ε-caprolactone (αClεCL) was resumed with formation of two activated chloride containing PCL tails. In the third step, the chlorides were converted into azides onto which alkynyl end-capped PEO was grafted by the copper-mediated Huisgen's cycloaddition [3 + 2], thus giving a “click” reaction. The thermal properties of the final copolymer and the precursors were analyzed by differential scanning calorimetry. The amphiphilicity of the final copolymer was confirmed by micellization in water.