Bromine Chain End Research Articles

Synthesis of New Type Polymers by Quasi-Living Atom Transfer Radical Polymerization.

Thanks to the polymer revolution of the 20th century, plastics are now part of our everyday lives. We use plastics as naturally as if they had always been an integral part of our lives. However, in the recent past, we were still predominantly using wood, metal, and glass objects, which were replaced by plastic products at an explosive rate. In many cases, this replacement has resulted in products with better physical, chemical, or biological properties. The changeover was too rapid, and the consequences were not recognized in time. This is evidenced by the huge scale of plastic pollution worldwide today. It is therefore in the interests of the future of both humans and animals that we must pay particular attention to the direct and indirect environmental impact of plastics introduced in animal husbandry. Starting from the tetrafunctional initiator produced as the first step of my work, poly(n-butyll acrylate) star polymers of different molecular weights were synthesized by atom transfer radical polymerization, using the so-called “core first” method. The bromine chain end of the produced star polymers was replaced by an azide group using a substitution reaction. Propalgyl telechelic PEGs were synthesized as a result of lattice end modification of poly(ethylene glycol) with different molecular weights. The azidated star polymers were connected with propalgyl telechelic PEGs using Huisgen’s “click” chemical process, and as a result of the “click” connection, amphiphilic polymer networks with several different structures were obtained.

Thiol-Bromo Click Reaction for One-Pot Synthesis of Star-Shaped Polymers.

Star-shaped polymers have unique physical properties and they are sought after materials in industry. However, the ease of synthesis is essential for translation of these materials into large-scale applications. Herein, a highly efficient synthetic method to prepare star-shaped polymers by combination of Cu-mediated reversible deactivation radical polymerization (Cu-RDRP) and thiol-bromo click reaction is described. Well-defined linear and block polymers with a very high bromine chain end fidelity are obtained via Cu-RDRP and subsequently react with multi-functional thiol compounds. High coupling efficiencies of larger than 90% are obtained owing to the quick and efficient reaction between thiols and alkyl bromides. Moreover, the arms of the obtained star-shaped polymers are linked via thioether bonds to the core, making them susceptible for oxidative degradation.

Polyacrylates Derived from Biobased Ethyl Lactate Solvent via SET-LRP.

The precise synthesis of polymers derived from alkyl lactate ester acrylates is reported for the first time. Kinetic experiments were conducted to demonstrate that Cu(0) wire-catalyzed single electron transfer-living radical polymerization (SET-LRP) in alcohols at 25 °C provides a green methodology for the LRP of this forgotten class of biobased monomers. The acrylic derivative of ethyl lactate (EL) solvent and homologous structures with methyl and n-butyl ester were polymerized with excellent control over molecular weight, molecular weight distribution, and chain-end functionality. Kinetics plots in conventional alcohols such as ethanol and methanol were first order in the monomer, with molecular weight increasing linearly with conversion. However, aqueous EL mixtures were found to be more suitable than pure EL to mediate the SET-LRP process. The near-quantitative monomer conversion and high bromine chain-end functionality, demonstrated by matrix-assisted laser desorption ionization time-of-flight analysis, further allowed the preparation of innovative biobased block copolymers containing rubbery poly(ethyl lactate acrylate) poly(ELA) sequences. For instance, the poly(ELA)- b-poly(glycerol acrylate) block copolymer self-assembled in water to form stable micelles with chiral lactic acid-derived block-forming micellar core as confirmed by the pyrene-probe-based fluorescence technique. Dynamic light scattering and transmission electron microscopy measurements revealed the nanosize spherical morphology for these biobased aggregates.

Synthesis of Highly Branched Copolymers in Microemulsion

AbstractAtom transfer radical copolymerization of monomer and inimer (containing initiating and monomer fragments in one molecule) is carried out in a microemulsion to produce branched copolymers with similar molecular weights but varied branching densities. The monomer 2‐(isobutyryloxy) ethyl methacrlyate (IEM) shares a similar structure as the selected inimer 2‐(2‐bromoisobutylryloxy) ethyl methacrylate (BIEM) and provides microemulsification with little change of micelle size upon varying the molar ratio of monomer to inimer (γ ) from 2 to 50. The copolymerization of IEM and BIEM in the discrete micellar space produces branched copolymers with similar molecular weights M n ≈ 2‐3 × 105, low dispersity M w/M n ≈ 1.2 but varied branching density. These branched copolymers contain dormant bromine chain ends that can be directly used as macroinitiators for polymerization of monomers to grow linear arms within microemulsion particles. Copolymers of IEM monomer and an acetal containing inimer (ABIEM) allow degradation of the branching units under acidic conditions to yield linear fragments from the parent structure. The concentration of the Cu(II)/ligand complex is varied from 2 to 4 mm in the polymerization of ABIEM to further tune the branching density, revealing that higher copper amount produces shorter linear fragments between branching points through improved deactivation.

Photoinduced atom transfer radical polymerization of methyl methacrylate with conducting polymer nanostructures as photocatalyst

Light-mediated control/living radical polymerization (CLRP) provides a convenient method to synthesize polymers with controlled molecular weight and narrow molecular weight distribution. However, high-energy wavelengths (such as UV light) and blue light are needed to initiate the polymerization, leading to unwanted side reactions. To overcome these defects, the use of long-wavelength light for light-mediated CLRP is highly desirable. In this work, photoinduced atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully carried out for the synthesis of polyMMA (PMMA) with predictable molecular weights (Mn,GPC) and narrow molecular weight distribution (Mw/Mn). This was achieved using one-dimensional nanopoly(diphenyl butadiyne) (nanoPDPB) as photocatalyst, which activated the dormant alkyl bromides initiator to reversibly produce propagating radicals at ambient temperature. Initiation and termination of polymerization were regulated by periods of light. The polymerization of MMA was accomplished by the radicals generated in the redox reaction of nanoPDPB with EBP. Both 1H nuclear magnetic resonance (1H NMR) spectroscopy and chain-end extension polymerization show highly preserved bromine chain-end functionality in the synthesized PMMA. nanoPDPB displays remarkable photophysical properties in the visible light region. The polymerization of MMA followed the first-order kinetics and the evolution of the Mn,GPC versus monomer conversion and Mw/Mn demonstrated the well-controlled polymerization process. The living character of heterogeneous photomediated ATRP with nanoPDPB as photocatalyst was successfully confirmed.

SET-LRP in Biphasic Mixtures of the Nondisproportionating Solvent Hexafluoroisopropanol with Water.

The fluorinated alcohol 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) is an especially effective solvent for solubilizing a wide range of polymers. However, the performance of HFIP as SET-LRP solvent has classically been questioned due to its poor Cu(I)X disproportionating properties. Taking advantage of the fast and quantitative disproportionation of Cu(I)X in water, SET-LRP in organic solvent/water mixtures rids the organic solvent of mediating this fundamental event. Here, the Cu(0) wire-catalyzed SET-LRP synthesis of well-defined poly(methyl acrylate)s and poly(butyl acrylate)s with narrow molecular weight distribution and near perfect bromine chain end functionality is reported in HFIP/water mixtures. The results reported here support the potential of HFIP/water mixtures in the preparation of more complex architectures including polymers with dual control over molecular weight and tacticity. Since HFIP is also a classic solvent for the denaturation of proteins this SET-LRP system is also expected to find applications in the grafting of protein.

Preparation of novel thioxanthone based polymeric photoinitiator for flexographic varnish and determination of their migration behaviour

Today, polymeric photoinitiators are good choice for initiation mechanism of UV-curable printing inks with their low migration potential. In this study, new thioxanthone-styrene polymeric photoinitiators were synthesized. Polystyrene that was synthesized by atom transfer radical polymerization (ATRP) was functionalized by cyclohexeneoxide and then reacted with thioxanthone-thioacetic acid. Piperazine was reacted with bromine chain end of polystyrene and final polymeric photoinitiator was obtained. Proton Nuclear Magnetic Resonance (1H NMR), Attenuated Total Reflectance- Fourier Transform Infrared Spectroscopy (ATR-FTIR), Gel Permeation Chromatography (GPC) and Ultraviolet-Visible Spectroscopy (UV–vis) analyses were confirmed the expected structures. The curing property of new polymeric photoinitiator was compared with a conventional thioxanthone printing formulation that is used in flexographic varnish. The photopolymerization kinetics were determined by Photo Differential Scanning Calorimetry (Photo-DSC) and the results showed that 83% of conversion was reached for thioxanthone-styrene polymeric photoinitiator with MW = 4200. The migration behavior was identified with Liquid Chromatography–Mass Spectrometry LC–MS. It was shown that thioxanthone based polymeric photoinitiator is usable in flexographic varnish and thioxanthone migration level is reduced with macrophotoinitiation.

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 (>90%) and low dispersity (∼1·1).

Effective End Group Modification of Poly(3-hexylthiophene) with Functional Electron-Deficient Moieties for Performance Improvement in Polymer Solar Cell.

A series of end-functionalized poly(3-hexylthiophene)s (P3HTs) were synthesized by end-capping with electron-deficient moieties (EDMs, oxadiazole (OXD) and triazole (TAZ)) to prevent the negative influence of bromine chain ends in the common uncapped P3HT in polymer solar cell (PSC) applications. On the basis of the electron-withdrawing capability of the planar OXD end groups, P3HT-end-OXD relative to the uncapped P3HT exhibits a raised absorption coefficient, extended exciton lifetime, and increased crystalline order in the blend with PCBM, leading to an effectual improvement in photovoltaic parameters. However, P3HT-end-TAZ has an opposite result even worse than that of the uncapped P3HT, arising from bulky TAZ end groups. As a consequence, P3HT-end-OXD gives a power conversion efficiency (PCE) of 4.24%, which is higher than those of the uncapped P3HT (3.28%) and P3HT-end-TAZ (0.50%). The result demonstrates that the EDM modification is a valuable method to tailor the structural defect of polymer chain ends. However, the efficacy is dependent on the structure of EDM.

Molecular Bottlebrushes with Bimodal Length Distribution of Side Chains

The structural details of bottlebrush polymers, specifically the grafting density and molecular weight distribution of side chains, influence their physical properties; however, they are difficult to analyze using conventional techniques. Herein we report the synthesis, characterization, and molecular imaging of bottlebrush macromolecules with both uniform and bimodal length distributions of poly(n-butyl acrylate) (PnBA) side chains. The densely grafted copolymers were prepared via the “grafting from” approach using atom transfer radical polymerization (ATRP). Bottlebrush macromolecules with both shorter and longer grafted chains were prepared by removal of a fraction of the bromine chain ends of the initial densely grafted brush by selective capping with 4-butoxy-TEMPO and subsequent chain extension of remaining active chains forming longer PnBA grafts. This procedure provided bottlebrush macromolecules with two distinct degrees of polymerization of the grafted side chains herein called bimodal grafts. A...

Hemoglobin and Red Blood Cells Catalyze Atom Transfer Radical Polymerization

Hemoglobin (Hb) is a promiscuous protein that not only transports oxygen, but also catalyzes several biotransformations. A novel in vitro catalytic activity of Hb is described. Bovine Hb and human erythrocytes were found to display ATRPase activity, i.e., they catalyzed the polymerization of vinyl monomers under conditions typical for atom transfer radical polymerization (ATRP). N-isopropylacrylamide (NIPAAm), poly(ethylene glycol) methyl ether acrylate (PEGA), and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were polymerized using organobromine initiators and the reducing agent ascorbic acid in acidic aqueous solution. In order to avoid chain transfer from polymer radicals to Hb's cysteine residues, the accessible cysteines were blocked by a reaction with a maleimide. The formation of polymers with bromine chain ends, relatively low polydispersity indices (PDI), first order kinetics and an increase in the molecular weight of poly(PEGA) and poly(PEGMA) upon conversion indicate that control of the polymerization by Hb occurred via reversible atom transfer between the protein and the growing polymer chain. For poly(PEGA) and poly(PEGMA), the reactions proceeded with a good to moderate degree of control. Sodium dodecyl sulfate (SDS) gel electrophoresis, circular dichroism spectroscopy, and time-resolved ultraviolet-visible (UV-vis) spectroscopy revealed that the protein was stable during polymerization, and only underwent minor conformational changes. As Hb and erythrocytes are readily available, environmentally friendly, and nontoxic, their ATRPase activity is a useful tool for synthetic polymer chemistry. Moreover, this novel activity enhances the understanding of Hb's redox chemistry in the presence of organobromine compounds.

Analysis of the Cu(0)-Catalyzed Polymerization of Methyl Acrylate in Disproportionating and Nondisproportionating Solvents

The kinetic and structural analyses of the polymer resulting from the Cu(0)/Me6-TREN-mediated polymerization of methyl acrylate (MA) initiated with methyl 2-bromopropionate (MBP) in solvents mediating different degrees of disproportionation are reported. Accurate analyses of the polymerization and of the resulting polymer demand a minimum combination of techniques that includes kinetics, GPC, 1H NMR, and MALDI-TOF both performed before and after chain-end functionalization via thio–bromo “click” chemistry and reinitiation experiments. At [MA]0/[MBP]0 = 222 the use of the disproportionating solvent DMSO generated first-order kinetics and 97% active chain ends of the polymer at 89% conversion. The less disproportionating solvent MeCN produced two linear first-order kinetics and a decrease of bromine chain-end functionality of the polymer with conversion, yielding 77% active chain ends at 89% conversion. The nondisproportionating solvent toluene, in the presence of TEMPO, produced two linear first-order kinetics with only 50% active chain ends of the polymer at 92% conversion.

Orthogonal modification of polymer chain-ends via sequential nitrile oxide–alkyne and azide–alkyne Huisgen cycloadditions

The α- and ω-chain-ends of well-defined polystyrene chains were functionalized using consecutive Huisgen cycloadditions. Firstly, an α-alkyne, ω-azido heterotelechelic polystyrene precursor was synthesized in three steps: (i) atom transfer radical polymerization in the presence of (1,1,1-trimethylsilyl)-2-propynyl 2-bromo-2-isobutyrate, (ii) deprotection of the alkyne function of the initiator and (iii) nucleophilic substitution of the bromine chain-end of the polymer with sodium azide. Afterwards, the chain-ends of the polymer were modified by successive nitrile oxide–alkyne cycloaddition (NOAC) and copper-catalyzed azide–alkyne cycloaddition (CuAAC). 2 Model building blocks were tested for NOAC, while 4 building blocks were studied for CuAAC. In all cases, the orthogonal combination of NOAC and CuAAC allowed the preparation of tailored heterotelechelic polymers.

Synthesis of poly(cyclohexene oxide)‐block‐polystyrene by combination of radical‐promoted cationic polymerization, atom transfer radical polymerization and click chemistry

AbstractThe combination of radical‐promoted cationic polymerization, atom transfer radical polymerization (ATRP) and click chemistry was employed for the efficient preparation of poly(cyclohexene oxide)‐block‐polystyrene (PCHO‐b‐PSt). Alkyne end‐functionalized poly(cyclohexene oxide) (PCHO‐alkyne) was prepared by radical‐promoted cationic polymerization of cyclohexene oxide monomer in the presence of 1,2‐diphenyl‐2‐(2‐propynyloxy)‐1‐ethanone (B‐alkyne) and an onium salt, namely 1‐ethoxy‐2‐methylpyridinium hexafluorophosphate, as the initiating system. The B‐alkyne compound was synthesized using benzoin photoinitiator and propargyl bromide. Well‐defined bromine‐terminated polystyrene (PSt‐Br) was prepared by ATRP using 2‐oxo‐1,2‐diphenylethyl‐2‐bromopropanoate as initiator. Subsequently, the bromine chain end of PSt‐Br was converted to an azide group to obtain PSt‐N3 by a simple nucleophilic substitution reaction. Then the coupling reaction between the azide end group in PSt‐N3 and PCHO‐alkyne was performed with Cu(I) catalysis in order to obtain the PCHO‐b‐PSt block copolymer. The structures of all polymers were determined. Copyright © 2010 Society of Chemical Industry

Rapid, Selective, and Reversible Nitroxide Radical Coupling (NRC) Reactions at Ambient Temperature

High activation of polystyrene with bromine end groups (PSTY-Br) to their incipient radicals occurred in the presence of Cu(I)Br, Me6TREN, and DMSO solvent. These radicals were then trapped by nitroxide species leading to coupling reactions between PSTY-Br and nitroxides that were ultrafast and selective in the presence of a diverse range of functional groups. The nitroxide radical coupling (NRC) reactions have the attributes of a “click” reaction with near quantitative yields of product formed, but through the reversibility of this reaction, it has the added advantage of permitting the exchange of chemical functionality on macromolecules. Conditions were chosen to facilitate the disproportionation of Cu(I)Br to the highly activating nascent Cu(0) and deactivating Cu(II)Br2 in the presence of DMSO solvent and Me6TREN ligand. NRC at room temperature gave near quantitative yields of macromolecular coupling of low molecular weight polystyrene with bromine chain-ends (PSTY-Br) and nitroxides in under 7 min even in the presence of functional groups (e.g., −≡, −OH, −COOH, −NH2, =O). Utilization of the reversibility of the NRC reaction at elevated temperatures allowed the exchange of chain-end groups with a variety of functional nitroxide derivatives. The robustness and orthogonality of this NRC reaction were further demonstrated using the Cu-catalyzed azide/alkyne “click” (CuAAC) reactions, in which yields greater than 95% were observed for coupling between PSTY-N3 and a PSTY chain first trapped with an alkyne functional TEMPO (PSTY-TEMPO-≡).

Synthesis of linear tetrablock quaterpolymers via atom transfer radical polymerization and a click coupling approach

We report the synthesis of a well-defined linear tetrablock quaterpolymer of poly(butyl acrylate)- b-polystyrene- b-poly(methyl acrylate)- b-poly(methyl methacrylate) by combining atom transfer radical polymerization (ATRP) and a click coupling approach. For this purpose, polystyrene- b-poly(butyl acrylate) (AB) was prepared by ATRP using macroinitiator as α-trimethylsilyl(TMS)-alkyne ω-bromo polystyrene. The α-(TMS) end of the AB diblock copolymer was deprotected using tetrabutylammonium fluoride (TBAF) in THF. The ω-azide end of the CD diblock copolymer was made from poly(methyl methacrylate)- b-poly(methyl acrylate) (CD) via transformation of the bromine chain end by a simple nucleophilic substitution reaction with NaN 3 in DMF. Click coupling between the ω-azide end in CD diblock copolymer with the α-alkyne end in the AB diblock copolymer was then performed by Cu 1-catalyzed (3+2) cycloaddition. Gel permeation chromatography (GPC), FT-IR and 1H NMR spectroscopy confirmed the successful formation of a linear ABCD tetrablock copolymer via ATRP and click coupling.

Cyclobutenyl Inimers as Versatile Initiators for Macromonomers Synthesis by Atom Transfer Radical Polymerization

Novel α-cyclobutenyl-containing inimers were used successfully for atom transfer radical polymerization (ATRP) of tert-butyl acrylate and styrene leading to narrow molecular weight α-cyclobutenyl-terminated macromonomers (Mn,SEC= 1600−11 500; PDI = 1.06−1.24). The ATRP processes followed first-order kinetics with respect to the monomer concentration. 1H NMR studies showed that the cyclobutenyl moiety in the initiator is stable during ATRP processes. The bromine chain end of resulting macromonomers has been used successfully for the syntheses of block copolymer-based α-cyclobutenyl macromonomers by ATRP. In particular, a range of well-defined polystyrene-b-poly(tert-butyl acrylate) macromonomers with various terminal α-cyclobutenyl groups were synthesized through this methodology.

Solvent Choice Differentiates SET-LRP and Cu-Mediated Radical Polymerization with Non-First-Order Kinetics

In order to assess the role of the solvent mediating the disproportionation of Cu(I)X into Cu(0) and Cu(II)X2 during SET-LRP, a series of polymerizations of methyl acrylate initiated with methyl 2-bromopropionate and catalyzed by Cu(0)/Me6-TREN at 25 °C in DMSO, MeCN, and their mixtures were investigated. These polymerizations proceed in a dissimilar manner. SET-LRP of MA in DMSO, a solvent that mediates disproportionation, was exemplary of “ultrafast living radical polymerization” with complete conversion in 45 min following the expected first-order kinetics and providing perfect fidelity of the structure of the polymer chain ends. When the polymerization was performed in MeCN, a solvent in which Cu(I)X species do not disproportionate, it displayed nonlinear first-order kinetics with a poor retention of the bromine chain end functionality. The lack of first-order kinetics and decrease of chain end functionality with conversion indicate a nonliving polymerization in MeCN. Increasing the concentration of DMSO in DMSO/MeCN mixtures provided a continuous transition from a nonliving to a living polymerization. The incompatibility of MeCN with SET-LRP lends support that disproportionation of Cu(I)X/N ligand to Cu(0) and Cu(II)X2/N ligand is the key step in SET-LRP.

Dibromotrithiocarbonate Iniferter for Concurrent ATRP and RAFT Polymerization. Effect of Monomer, Catalyst, and Chain Transfer Agent Structure on the Polymerization Mechanism

An iniferter comprising a trithiocarbonate (TTC) moiety and two bromine chain ends was prepared and used to successfully conduct, independently or concurrently, atom transfer radical polymerization...

Synthesis and characterization of low molecular weight poly(methyl acrylate)-b-polystyrene by a combination of ATRP and click coupling method

The combination of atom transfer radical polymerization (ATRP) and click chemistry was employed for the efficient preparation of well-defined block copolymers. Bromo terminated poly(methyl acrylate) (pMA-Br) was prepared by an ATRP initiator, ethyl-2-bromoisobutyrate (EBiB). Subsequently, the bromine chain end of pMA-Br was converted to an azide group by simple nucleophilic substitution reaction. α-Alkyn-ω-bromo-functionalized polystyrene was also synthesized by ATRP using the alkyn-functionalized initiator, propargyl-2-bromoisobutyrate (PgBiB). In both cases, the conversion was limited to a low level to ensure a high degree of chain end functionality. Then the coupling reaction between the azide end group in pMA-N3 and alkyn-functionalized PgBiB-pSt was performed by Cu(I)catalysis. This coupling reaction was monitored by gel permeation chromatography (GPC). The synthesized block copolymer was characterized by FT-IR,1H-NMR spectroscopy and1H-1H COSY correlation spectroscopy.