Ethyl 2-bromoisobutyrate Research Articles

Separable and recyclable SBA-15 based catalyst for metal-free ATRP

The aminoated SBA-15 (SBA-15-NH2) was obtained by the condensation reaction between the hydroxyl group on the surface of SBA-15 and the ethoxy group of 3-aminopropyl triethoxysilane (KH550) coupling agent. And then the fluorescein acyl chloride (Flu-Cl) or rhodamine B acyl chloride (RB-Cl) was loaded onto SBA-15 surface to gain two kinds of SBA-15 based catalysts (SBA-15-Flu and SBA-15-RB) via the reaction between the amino group of SBA-15-NH2 and the acyl chloride group of Flu-Cl or RB-Cl. The metal-free ATRP of methyl methacrylate (MMA) was carried out under 365 nm UV light using SBA-15 based catalyst as photocatalyst, and ethyl 2-bromoisobutyrate (EBIB) as initiator. The structure of the two SBA-15 based catalysts was confirmed by fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and thermogravimetry analysis (TGA). The morphology and surface area of SBA-15 before and after modification were observed by scanning electron microscopy (SEM) and brunauer emmett teller (BET) respectively. The results showed that Flu-Cl and RB-Cl have been successfully loaded onto SBA-15 surface. Gel permeation chromatograph (GPC) and kinetic experiments illustrated the polymerization process was controllable and the molecular weight distribution was relatively narrow, which conforms to the characteristics of living radical polymerizations. After polymerization, the SBA-15 based photocatalyst was separated by simple centrifugation and recycled three or four times for metal-free ATRP. In these cyclic catalytic processes, the separated SBA-15 based photocatalyst exhibited excellent catalytic effect, the polymerization product is pure and has no residual catalyst.

Features of Methyl Methacrylate Polymerization Mediated by Methylene Blue and Ethyl 2-Bromoisobutyrate under Photoirradiation Conditions

Features of Methyl Methacrylate Polymerization Mediated by Methylene Blue and Ethyl 2-Bromoisobutyrate under Photoirradiation Conditions

Features of Methyl Methacrylate Polymerization Mediated by Methylene Blue and Ethyl 2-Bromoisobutyrate under Photoirradiation Conditions

Using methyl methacrylate polymerization as an example, the features of polymer synthesis in the presence of the catalytic system [methylene blue + ethyl 2-bromoisobutyrate] at room temperature under visible light irradiation are investigated. The effect of polymerization conditions, including the light irradiation wavelength and various structure activators, on the monomer conversion and molecular weight characteristics of polymers is estimated. It is shown that polymerization can proceed in the controlled mode under mild temperature conditions according to the atom transfer mechanism (Metal Free Atom Transfer Radical Polymerization) to high conversions at low photocatalyst concentrations.

Recyclable magnetic Fe3O4 supported photocatalyst for the metal-free ATRP

Silica layer coated Fe3O4 magnetic nanoparticles (Fe3O4@SiO2) were used to support an photocatalyst rhodamine B (RB) (Fe3O4@SiO2-RB) for the metal-free atom transfer radical polymerization (metal-free ATRP) of methyl methacrylate (MMA) for easy separation and recycling of the catalysts. The metal-free ATRP of MMA was carried out under 365 nm UV light using Fe3O4@SiO2-RB as photocatalyst, and ethyl 2-bromoisobutyrate (EBIB) as initiator. The structure of Fe3O4@SiO2-RB was demonstrated by FT-IR, XPS, XRD and TG. The changes of morphology and specific surface area of Fe3O4 before and after modification were observed by SEM and BET. For the metal-free ATRP reaction, the polymerization process was controllable, the molecular weight was uniform and end of the molecular chain was active. The Fe3O4@SiO2-RB catalyst can be recycled through simple magnetic separation to catalyze polymerization in a controlled manner for three times, and the catalytic activity of the three polymerization reactions decreased slightly in turn. The implementation of this strategy demonstrates that the photoinitiated catalysts can be recovered and reused for subsequent light-induced ATRP.

UV-mediated atom transfer radical polymerization of acrolein

In this paper, the polymerization of acrolein (A) via UV-mediated atom transfer radical polymerization (ATRP) is reported. The optimization of the experimental conditions of the polymerization is investigated, and it shows that dimethyl sulfoxide as solvent, ethyl 2-bromoisobutyrate (EBIB) and fluorescein (FL) as catalyst, and [A]0/[EBIB]0/[FL]0 = 200/1/0.1 in the period of 5 h at 47 °C are suitable conditions for the reaction. In this way, the yield of the polymer is 24.5%. The glass transition temperature and melting point of polyacrolein characterized by differential scanning calorimetry are 115.5 °C and 165.7 °C, respectively. At low conversion, the polymerization conforms to be the first-order kinetics reaction. The dependence of polymerization on light source is proved by “on/off” light source experiment. In short, this study opens up a new way for the ATRP of acrolein, and the polyacrolein with abundant aldehyde groups can be used in the fields of biomedical labeling, immobilization carrier and adsorption of organic amines.

Atom-transfer radical homo- and copolymerization of carbazole-substituted styrene and perfluorostyrene

Atom-transfer radical polymerization of 9-(4-vinylphenyl)carbazole (M1) and 9-(2,3,5,6-tetrafluoro-4-vinylphenyl)carbazole (M2) has been investigated using CuCl/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine as catalyst and ethyl 2-bromoisobutyrate as an initiator. The polymerization of the monomers proceeded in a living fashion affording polymers with controlled molecular weight (Mn = 5000 g mol−1 to 32000 g mol−1) and relatively low polydispersity (Đ=1.2–1.5). The kinetic investigations showed that M2 polymerized at the faster rate as compared to M1. Block copolymers were successfully prepared starting from the polymerization of more reactive M2 followed by addition of M1. The same initiating system also induced living radical copolymerization of these monomers giving random copolymers. Usage of tetrafunctional initiator pentaerythritol tetrakis(2-bromoisobutyrate) in conjunction with CuCl/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine as catalyst allowed to synthesize star-shaped linear and random copolymers from M1 and M2 with controlled molecular weight (up to Mn = 25000 g mol−1) and low polydispersity (Đ<1.5). The thermal, photophysical and electrochemical properties of the synthesized linear and star-shaped polymers and copolymers were estimated. It was shown that photophysical properties of copolymers can be tuned by changing the copolymer composition.

Cyclic amines homobimetallic ruthenium pre-catalysts bearing bidentate phosphine and their dual catalytic activity for the ring-opening metathesis and atom-radical polymerizations

A series of [RuCl(dppb)(μ-Cl)3Ru(dppb)(amine)] complexes, where amine is pyrrolidine (1), piperidine (2) or perhydroazepine (3), were synthesized and characterized by elemental analysis, FTIR, UV–Vis, and 1H, 13C{1H} and 31P{1H} NMR spectroscopy. The electrochemistry properties of the complexes 1–3 were investigated by cyclic voltammetry and exhibited two successive single-electron oxidation processes. The presence of two redox pairs suggests the formation of a dimeric species in which two different fragments, {Ru(amine)(dppb)} and {RuCl(dppb)}, were connected via three μ-chloro bridges. The complexes 1–3 were evaluated as catalytic precursors for ROMP of norbornene (NBE) and norbornadiene (NBD), as well as for ATRP of methyl methacrylate (MMA). The polynorbornene (polyNBE) syntheses via ROMP using the complexes 1–3 as pre-catalysts were assessed under reaction conditions of [EDA]/[Ru] = 28 (5 μL) and [NBE]/[Ru] = 5000 as a function of time at 25 or 50 °C. Polymerization of MMA via ATRP was conducted using the complexes 1–3 in the presence of ethyl 2-bromoisobutyrate (EBiB) as initiator. Differences in the catalytic activities and polymerization controls were observed in the order 3 > 2 >1 for both reactions. The activities were discussed considering the steric hindrance and electronic characteristics of the amines as ancillary ligands in the metal center using cyclic voltammetry and NMR studies.

Pickering emulsion of metal-free photoinduced electron transfer-ATRP stabilized by cellulose nanocrystals

The development of metal-free photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) in Pickering emulsion by cellulose nanocrystals (CNCs) has successfully investigated. In the presence of ethyl 2-bromoisobutyrate (initiator) and triethylamine (additives), Eosin Y (photocatalyst) can effectively achieve the controllable polymerization of methyl methacrylate utilize CNCs as stabilizer. The polymerization in Pickering emulsion has relatively higher stability. The polymerizations of MMA showed typical “living”/controlled characteristics with controlled molecular weights (150,100–219,100 g/mol) and low Mw/Mn (1.10–1.25). CNCs can not only be recycled, but also can be applicable as one of the most robust “green” emulsifier for PET-ATRP in Pickering emulsion.

Salt-Free Reduction of Transition Metal Complexes by Bis(trimethylsilyl)cyclohexadiene, -dihydropyrazine, and -4,4'-bipyridinylidene Derivatives.

Chemical reduction of transition metals provides the corresponding low-valent transition metal species as a key step for generating catalytically active species in metal-assisted organic transformations and is a fundamental unit reaction for preparing organometallic complexes. A variety of metal-based reductants, such as metal powders and organometallic reagents of alkali and alkaline-earth metals, have been developed to date to access low-valent metal species. During the reduction, however, reductant-derived metal salts are formed as reaction waste, some of which often interact with the reactive low-valent metal center, thereby disrupting the catalytic performance and hampering the isolation of organometallic complexes as a result of salt coordination to the coordinatively unsaturated vacant and active sites and the formation of thermally unstable ate complexes. In this Account, we emphasize the synthetic utility and versatility of organic reductants containing two trimethylsilyl groups, i.e., 1,4-bis(trimethylsilyl)cyclohexa-2,5-diene (1a) and its methyl derivative (1b), 1,4-bis(trimethylsilyl)dihydropyrazine (2a) and its dimethyl (2b) and tetramethyl (2c) derivatives, and 1,1'-bis(trimethylsilyl)-4,4'-bipyridinylidene (3), leading to the reduction of various kinds of metal compounds in a salt-free fashion by release of two electrons together with the coproduction of easily removable (hetero)aromatics and trimethylsilyl derivatives from these organic reductants 1-3. When homoleptic chlorides of group 5 and 6 metals are treated with 1a and 1b, in situ-generated highly reactive low-valent metal species react with redox-active molecules such as ethylene, α-diimines, and α-diketones to produce metallacyclopentane, (ene-diamido)metal, and (ene-diolato)metal complexes, respectively. The advantage of the salt-free protocol is further exemplified in the low-valent titanocene-catalyzed Reformatsky-type reaction when 2c is used as a reductant: the yield of the product using the organosilicon reductant is higher than that when manganese powder is used as the reductant for the catalytic Reformatsky-type reaction of ethyl 2-bromoisobutyrate and its derivatives with various aldehydes. Moreover, when halides, carboxylates, and acetylacetonate compounds of late transition metals and main-group elements are treated with the organosilicon reductant 2c, metal(0) particles are smoothly precipitated under mild conditions. Among them, metallic nickel(0) nanoparticles are applicable to reductive biaryl formation and reductive cross-coupling of aryl halides/aryl aldehydes. In addition, reduction of the heterogeneous catalysts on a solid supporting matrix was also achieved by this salt-free reduction method; volatile byproducts are easily removed from the catalyst surface without suppressing the catalytic performance. Thus, the salt-free reduction strategy is a very powerful synthetic method that can be extended to various metals throughout the periodic table.

SYNTHESIS OF POLYMERS BASED ON STEARYL METHACRYLATE AND THEIR USE AS ADDITIVES FOR DIESEL FUEL

In this article the features of controlled radical polymerization of stearyl methacrylate in the presence of copper-based compounds in combination with nitrogen-containing ligands such as tris[2-(dimethylamino)ethyl]amine and tris[(2-pyridyl)methyl]amine were studied. The ethyl 2-bromoisobutyrate was used as the initiator of the polymerization process. The synthesized polymers were characterized by gel permeation chromatography and MALDI-TOF time-of-flight mass spectrometry. It was found that the proposed catalytic systems allow conducting controlled radical polymerization of stearyl methacrylate according to the Atom Transfer Radical Polymerization mechanism at relatively mild temperature conditions. It was revealed that the nature of the organic ligand has a significant effect on the rate of polymerization and the molecular-weight characteristics of the synthesized samples. Using the copper(I) bromide catalytic system in combination with tris[(2-pyridyl)methyl]amine as a ligand at reagents molar ratio of 1:4, the polymerization of stearyl methacrylate proceeded with high reaction rate to deep conversions in a wide range of molecular weights. The observed linear growth of the molecular weight of the polymer with increasing conversion and low polydispersity index of the synthesized polymers being at the level of 1.19-1.29, considered as an evidence of the controlled mode of polymerization. The influence of the molecular weight characteristics of polymers based on stearyl methacrylate on the low-temperature properties of diesel fuel of specification24-2000 produced by OOO «LUKOIL-Nizhegorodnefteorgsintez» was evaluated using a low-temperature analyzer MX-700 (PE-7200I) in accordance with the requirements of Russian (GOST 5066-91 and GOST 20287-91) and the international (ISO-3016) standards for the quality of petroleum products. It was established that the synthesized polymers can be used as additives that reduce the temperature range of solidification of environmentally clean diesel fuels, while the molecular weight of polystearyl methacrylate has a significant effect on the depressor properties of the fuel.Forcitation:Simanskaya K.Yu., Grishin I.D., Grishin D.F. Synthesis of polymers based on stearyl methacrylate and their use as additives for diesel fuel. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 82-89

Accessible ring opening metathesis and atom transfer radical polymerization catalysts based on dimethyl sulfoxide ruthenium(II) complexes bearing N-heterocyclic carbene ligands

Dimethyl sulfoxide ruthenium(II) complexes of N-heterocyclic carbenes derived from cycloalkylamines (cycloalkyl = cyclopentyl (1a), cyclohexyl (1b), cycloheptyl (1c), and cyclooctyl (1d)) were synthesized: [RuCl2(S-dmso)2(IPent)] (2a), [RuCl2(S-dmso)2(IHex)] (2b), [RuCl2(S-dmso)2(IHept)] (2c), and [RuCl2(S-dmso)2(IOct)] (2d). The imidazolium salts 1a-1d were characterized by FTIR, UV–vis, and 1H and 13C NMR spectroscopy, while their respective dimethyl sulfoxide ruthenium(II) complexes (2a-2d) were characterized by elemental analysis, FTIR, UV–vis, 1H and 13C NMR, and cyclic voltammetry. The complexes 2a-2d were evaluated as catalytic precursors for ROMP of norbornene (NBE) and for ATRP of methyl methacrylate (MMA). The polynorbornene (polyNBE) syntheses via ROMP using the complexes 2a-2d as pre-catalysts were evaluated under reaction conditions of [EDA]/[Ru] = 28 (5 μL), [NBE]/[Ru] = 5000 at 50 °C as a function of time. The polymerization of MMA via ATRP was conducted using the complexes 2a-2d in the presence of ethyl 2-bromoisobutyrate (EBiB) as the initiator. All tests were using the molar ratio [MMA]/[EBiB]/[Ru] = 1000/2/1 and conducted at 85 °C. The linear correlation of ln([MMA]0/[MMA]) and time clearly indicates that the concentration of radicals remains constant during the polymerization and that the ATRP of MMA mediated by 2a-2d proceeds in a controlled manner.

Controlling/living polymerization of MMA with RGO/BiVO4 as photoinitiator

ABSTRACTIn this study, reduced grapheme oxide (RGO)/BiVO4 composite was prepared and characterized by FT-IR, XRD, and UV spectrum. Photo-chemically-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully performed at 25°C in N,N-dimethylformamide (DMF) with RGO/BiVO4 as photoinitiator, FeCl3·6H2O/triphenylphosphine (PPh3) as catalyst, and ethyl 2-bromoisobutyrate as ATRP initiator. MMAs were polymerized in a controlled manner under ultraviolet (UV) light and sunlight conditions. The results show that a first-order kinetics model was obeyed up to higher conversion. The reaction gave well-controlled PMMA with Mn,GPC close to the theoretical value and a narrow MWD (Mw/Mn<1.5). The experiments of light on and off reveal the photoredox cycle between Fe(III) and Fe(II) species. The living character was further verified by the chain extension experiments.

Well-Defined Polymer-Brush-Coated Rod-Shaped Particles: Synthesis and Formation of Liquid Crystals

The surface of hematite rods (α-Fe2O3 rods; aspect ratio = 6, semimajor axis = 600 nm) was modified by surface-initiated atom transfer radical polymerization (SI-ATRP). The copper-catalyzed SI-ATRP of methyl methacrylate (MMA) was conducted on the surface of the initiator-fixed α-Fe2O3 rods using a free (sacrificial) initiator, ethyl 2-bromoisobutyrate. Well-defined poly(MMA) (PMMA) brushes were densely grafted on the rods with a chain density of up to 0.7 chains/nm2. These hybrids composed of a rod-shaped particle as the core and a PMMA brush as the shell were highly dispersed in any of “good solvents” for PMMA. Double-layer (organic layer/inorganic layer)-coated α-Fe2O3 rods were also fabricated by grafting PMMA brushes on the surface of silica-coated α-Fe2O3 rods. The α-Fe2O3 cores of the hybrid rods were etched with hydrochloric acid, affording hollow hybrid rods. Polarized optical microscopy confirmed the formation of lyotropic liquid crystals by the rods grafted with polymer chains of a proper length.

Greener solvent systems for copper wire-mediated living radical polymerisation

Copper wire-mediated living radical polymerisation (LRP) is a powerful tool that provides numerous opportunities for the development of new materials. It requires very low catalyst loading and mild reaction conditions; however, it typically involves the use of organic solvents. The authors have investigated the use of greener solvent systems to replace traditional volatile organic solvents without detrimentally affecting polymerisation. The effects of these alternative solvents on the control over polymerisation and polymer characteristics were investigated for the polymerisation of methyl acrylate initiated by ethyl 2-bromoisobutyrate. Copper wire-mediated LRP was conducted in dimethyl sulfoxide (DMSO), polyethylene glycol (PEG) and polypropylene glycol (PPG) and binary mixtures of PEG–DMSO, PEG–ethanol, PPG–DMSO and PPG–ethanol with total solvent volume fractions of 33 and 50%. Secondary solvent fractions in the binary mixtures were examined at 10 and 25% of the total solvent volume. The two most effective greener solvent systems were 33% v/v of 75% PEG–25% ethanol and 33% v/v of 75% PPG–25% ethanol. Both were shown to provide excellent control over polymerisation and a high degree of livingness. The poly(methyl acrylate) produced in these solvent systems retained high bromine chain-end functionality (&gt;90%) and low dispersity (∼1·1).

Photoinduced controlled/“living” polymerization of methyl methacrylate with flavone as photoinitiator

ABSTRACTPhotochemically mediated controlled/“living” polymerization of methyl methacrylate (MMA) triggered by flavone was studied. The polymerization was performed in ethanol at ambient temperature with CuBr2/Tris(2‐dimethylaminoethyl)amine (Me6TREN) as complex catalyst and ethyl 2‐bromoisobutyrate (EBiB) as initiator. The molar mass of poly(methyl methacrylate) (PMMA) was obtained and exhibited relatively narrow molecular weight distribution (Mw/Mn) which was characterized by gel permeation chromatography (GPC). Chain extension further indicated that the living nature was maintained in the photopolymerization system. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43845.

Preparation of MWNT-g-poly(2,5-benzoxazole) (ABPBO) with excellent electromagnetic absorption properties in the Ku band via atom transfer radical polymerization (ATRP)

A novel approach is developed to study the electromagnetic wave absorption properties based on chemical molecular structure in this work. The MWNT-g-ABPBO composite with core–shell structure, initiated by macromolecule MWNT-benzocyclobutene(ethyl 2-bromoisobutyrate) (MWNT-BCB(EBIB)) via ATRP method, exhibits outstanding electromagnetic wave absorption properties in the Ku band. Traditionally, the electromagnetic wave absorption occurs around the wavelength of 3 cm (at 8 GHz), while the studies on materials with absorption properties at the wavelength slightly under 1.5 cm (at 20 GHz), namely part of the Ku band, are limited. The absorption peak of MWNT-g-ABPBO composite, with the thickness of 2.8 mm, can reach −36 dB at 17.4 GHz, because of the excellent impedance matching between the initiator and monomers bearing highly conjunction chemical structure introduced by ATRP. Meanwhile, the maximum reflection loss (RL) was −47 dB at the frequency of 15.5 GHz and the effective absorption bandwidth (<−10 dB) is from 13 to 18 GHz.

Exploration of highly active bidentate ligands for iron (III)-catalyzed ATRP

Novel highly active substituted P-N ligands were found to be remarkably efficient for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and butyl methacrylate (BMA). The reaction was catalyzed by a high oxidation state metal (FeX3) coupled with ethyl-2-bromoisobutyrate (EBriB) as an ATRP initiator. MMA polymerization was examined by the gradual addition of FeX3 and the complete transformation of uncontrolled ATRP (PDI∼1.59) to a controlled polymerization system (PDI∼1.13) was observed. The polymerizations were well controlled with a linear increase in the mean molecular weight (Mn) and monomer conversion reached up to 90% without complications. In the case of the DTBP ligand, the experimental molecular weights matched the theoretical values well and the PDIs were narrower (<1.2) compared to the other ligands. Furthermore, the potentially active catalyst (FeBr3/DTBP) was used successfully for the polymerization of MMA at a 50-ppm catalyst loading. The probable mechanism using FeX3 without an external additive was also determined.

Synthesis of N-(2 amino benzothiazole) methacylamide monomer and its copolymers for antimicrobial coating application by RAFT polymerization

ABSTRACTMonomer with thiazole moiety was synthesized and copolymerized with butyl acrylate and methyl methacrylate by reversible addition fragmentation chain transfer emulsion polymerization. The chain transfer agent was synthesized using N-ethyl piperazine, carbon disulfide, and ethyl 2-bromoisobutyrate. The wt% of monomer was varied from 3, 5, 7, 9, and 12 respectively. A antimicrobial activities of monomer and its copolymers were screened against E. coli, B. subtilis, C. albicans, and Aspergillus niger microorganisms. The synthesized monomer and chain transfer agent were characterized by 1H NMR, FTIR, and mass spectral analysis, whereas emulsion copolymers were characterized for their molecular weight, particle size, and FTIR analysis.

Low Concentration Limitations of Catalyst and Conventional Free Radical Polymerization in ICAR ATRP of Butyl Methacrylate With PMDETA as the Ligand

Low concentration limitations of the catalyst and conventional free radical polymerization are investigated in the system of initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) of butyl methacrylate (BMA), in which 2,2-azobisisobutyronitrile (AIBN) is used as a reducing agent, pentamethyldiethylenetriamine (PMDETA) as a ligand, copper bromide (CuBr2) as a catalyst and ethyl 2-bromoisobutyrate (EBiB) as an initiator. Results show that conventional radical polymerization happens in the early stage of the ICAR ATRP of BMA when the amounts of AIBN are 3∼25 times of the catalyst. And with the increase of the conversion, the BMA polymerization solely conducts the controlled radical polymerization (CRP). The low concentration limitations (based on monomer) of the catalyst required in ICAR ATRP of BMA with good controllability are found to be closely related to the molar ratio of initiator to catalyst, which is determined by the stability of the catalyst/ligand complex. The smaller molar ratio of initiator to catalyst allows lower concentration limitations of the catalyst.

Prop-2-yn-1-yl 2-Bromo-2-methylpropanoate: Identification and Suppression of Side Reactions of a Commonly Used Terminal Alkyne-Functional ATRP Initiator

The atom transfer radical polymerization (ATRP) of styrene was investigated using the popular alkyne-functional initiator prop-2-yn-1-yl 2-bromo-2-methylpropanoate (PBiB). The polymerization kinetics and evolution of molecular weight as a function of monomer conversion were systematically studied with PBiB and similar initiators with protecting groups at the reactive propargylic and terminal acetylenic sites. These studies were compared to control studies using the nonfunctional initiator ethyl 2-bromoisobutyrate. As confirmed by NMR analysis of a model reaction, the terminal alkynes undergo oxidative alkyne–alkyne coupling under ATRP conditions, resulting in polymers with bimodal molecular weight distributions. This side reaction is significant because it diminishes the orthogonality of ATRP/copper-catalyzed azide–alkyne cycloaddition procedures as well as the control of ATRP.