Bromine End Groups Research Articles

Chemical recycling of bromine-terminated polymers synthesized by ATRP.

Chemical recycling of polymers is one of the biggest challenges in materials science. Recently, remarkable achievements have been made by utilizing polymers prepared by controlled radical polymerization to trigger low-temperature depolymerization. However, in the case of atom transfer radical polymerization (ATRP), depolymerization has nearly exclusively focused on chlorine-terminated polymers, even though the overwhelming majority of polymeric materials synthesized with this method possess a bromine end-group. Herein, we report an efficient depolymerization strategy for bromine-terminated polymethacrylates which employs an inexpensive and environmentally friendly iron catalyst (FeBr2/L). The effect of various solvents and the concentration of metal salt and ligand on the depolymerization are judiciously explored and optimized, allowing for a depolymerization efficiency of up to 86% to be achieved in just 3 minutes. Notably, the versatility of this depolymerization is exemplified by its compatibility with chlorinated and non-chlorinated solvents, and both Fe(ii) and Fe(iii) salts. This work significantly expands the scope of ATRP materials compatible with depolymerization and creates many future opportunities in applications where the depolymerization of bromine-terminated polymers is desired.

Synthesis of tetrakis bromine terminated phthalocyanine and its methylmethacrylate polymers via ATRP

A phthalocyanine (Pc) initiator, tetrakis(2-bromopropyloxyester)ethylthiophthalocyaninatozinc(II) (ZnPc-Br), was prepared and successfully applied to atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) for the first time. Bromine end groups of the synthesized Pc took part in the initiation of the MMA chain growth. Polymerization was demonstrated by monomodal molecular weight distribution of the synthesized polymers and their increasing molecular weight behavior with reaction time. UV-Vis absorption, fluorescence, and transmittance properties of the polymers were also examined. The results indicate that the ZnPc-Br-based initiator is potentially applicable in ATRP applied to MMA in order to obtain and develop functional acrylic materials.

Cross-Linking of a Hydrophilic, Antimicrobial Polycation toward a Fast-Swelling, Antimicrobial Superabsorber and Interpenetrating Hydrogel Networks with Long Lasting Antimicrobial Properties.

A hemocompatible, antimicrobial 3,4en-ionene (PBI) derived by polyaddition of trans-1,4-dibromo-2-butene and N,N,N',N'-tetramethyl-1,3-propanediamine was cross-linked via its bromine end groups using tris(2-aminoethyl)amine (TREN) to form a fast-swelling, antimicrobial superabsorber. This superabsorber is taking up the 30-fold of its weight in 60 s and the granulated material is taking up 96-fold of its weight forming a hydrogel. It fully prevents growth of the bacterium Staphylococcus aureus. The PBI network was swollen with 2-hydroxyethyl acrylate and glycerol dimethacrylate followed by photopolymerization to form an interpenetrating hydrogel (IPH) with varying PBI content in the range of 2.0 to 7.8 wt %. The nanophasic structure of the IPH was confirmed by atomic force microscopy and transmission electron microscopy. The bacterial cells of the nosocomial strains Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa are killed on the IPH even at the lowest PBI concentration. The antimicrobial activity was retained after washing the hydrogels for up to 4 weeks. The IPHs show minor leaching of PBI far below its antimicrobial active concentration using a new quantitative test for PBI detection in solution. This leaching was shown to be insufficient to form an inhibition zone and killing bacterial cells in the surroundings of the IPH.

Molecular Weight Distribution of Living Chains in Polystyrene Prepared by Atom Transfer Radical Polymerization.

Living and dead chains of a polystyrene synthesized by atom transfer radical polymerization were separated and characterized by high performance liquid chromatography (HPLC), size exclusion chromatography (SEC), NMR, and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The bromine end group in the living chain was quantitatively converted to a hydroxyl end group via first azidation and subsequent copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction with propargyl alcohol. The living chains bearing a polar end group are fully resolved from the unmodified dead chains by HPLC separation using a bare silica stationary phase. Molecular weight distributions (MWD) of the living and dead chain are characterized by SEC and MALDI-MS. The MWD of the living chains is close to a Poisson distribution. Interestingly, the elution peak of the living chains in the HPLC separation split into two. The peak split is attributed to the diastereomeric structure of the chain end by NMR and MALDI-MS analyses.

Synthesis of novel polymer brushes of poly(acrylonitrile-g-N,Nʹ-dimethylaminoethyl methacrylate) by nitrile modification

Functional polymer brushes of poly(acrylonitrile-g-N,Nʹ-dimethylaminoethyl methacrylate) were efficiently synthesized by a novel approach of combining Cu(0)-mediated controlled/“living” radical polymerization and nitrile click chemistry. The poly(acrylonitrile-g-N,Nʹ-dimethylaminoethyl methacrylate) as a promising material exhibited excellent hydrophile–lipohile balance in the process of self-assembly and could autonomously develop the orderly structure micelle in N,Nʹ-dimethylformamide/water mixture solvent for the potential application of a new drug delivery carrier. In the process of self-assembly, polyacrylonitrile acted as a backbone of the functional polymer brushes due to its hydrophobic feature and poly(N,Nʹ-dimethylaminoethyl methacrylate) as the branch of functional polymer brushes due to its hydrophilic characteristic, which both were prepared by Cu(0)-mediated controlled/“living” radical polymerization with ethyl-bromoisobutyrate as initiator. Poly(N,Nʹ-dimethylaminoethyl methacrylate) containing azide end group was synthesized by substitution reaction of poly(N,Nʹ-dimethylaminoethyl methacrylate) containing bromine end groups with sodium azide in N,Nʹ-dimethylformamide. The click reaction between the nitrile of polyacrylonitrile and the azide group of poly(N,Nʹ-dimethylaminoethyl methacrylate) was carried out under ammonium chloride as catalyst in N,Nʹ-dimethylformamide. The polymer was further confirmed by GPC, FTIR, 1H NMR and TGA. Meanwhile, the micelles with different morphologies were observed by TEM, and the particle diameter distribution of self-assembled micelle from the PAN-g-PDMAEMA brushes was determined by DLS.

Suppression of surface pattern formation in spin‐coated polymer films by the addition of polydimethylsiloxane‐grafted silica nanoparticles

Polydimethylsiloxane (PDMS)‐grafted nanoparticles and PDMS were added, respectively, to inhibit the dewetting of polymer films and the formation of surface patterns in spin coating. Uniform and flat films were successfully achieved with the addition of PDMS‐grafted silica nanoparticles or PDMS. Time‐of‐flight secondary ion mass spectrometry depth profiling indicated that PDMS‐grafted silica nanoparticles and PDMS preferentially segregated to the surface. A high concentration of bromine end groups was observed at the interface. The surface layer of PDMS or PDMS‐grafted silica nanoparticles can decrease the surface tension of the polymer solutions and reduce the evaporation rates of the solvents, providing more time for the bromine end groups to anchor themselves at the silicon substrates. Copyright © 2016 John Wiley & Sons, Ltd.

Iso-Oriented Fluorescent Colloidal Nanocrystals of Bis-Cyanostyryl Thiophenes: Crucial Secondary Halogen Interactions toward Stability and Transport

Water-dispersible, single-crystalline, and fluorescent colloidal crystals with curved edges were fabricated from π-conjugated chromophores 2,5-bis(α-cyano-4-bromostyryl)thiophene (CN-BST) and 2,5-bis(α-cyanostyryl)thiophene (CN-ST) via reprecipitation. The colloidal crystal growth occurred in a nonclassical pathway through alignment of seed particles. The effects of torsion and planarity were examined through DFT calculations and photoluminescence spectroscopy. The bromine end groups were shown not to have a significant role in bringing absorption or fluorescent spectral changes, however, had endowed the molecules to interact in an angular geometry, conferring additional stability and rigidity to the CN-BST colloidal crystals. Most importantly, secondary Br–Br interactions in the solid state shielded and stabilized the associative dimeric interactions of the type, (i) face-to-face π-stack, (ii) slip-stack, (iii) C–H···N, and (iv) C–H···π with different strengths. Both classes of colloidal crystals exhibit...

Novel antifouling surface with improved hemocompatibility by immobilization of polyzwitterions onto silicon via click chemistry

A novel procedure is presented to develop an antifouling silicon surface with improved hemocompatibility by using a zwitterionic polymer, poly(sulfobetaine methacrylate) (polySBMA). Functionalization of the silicon surface with polySBMA involved the following three steps: (1) an alkyne terminated polySBMA was synthesized by RAFT polymerization; (2) a self-assembled monolayer with bromine end groups was constructed on the silicon surface, and then the bromine end groups were replaced by azide groups; and (3) the polySBMA was attached to the silicon surface by azide–alkyne cycloaddition click reaction. Membrane characterization confirmed a successful silicon surface modification with almost 100% coverage by polySBMA and an extremely hydrophilic surface after such modification. The polySBMA-modified silicon surface was found to have excellent anti-nonspecific adsorption properties for both bovine serum albumin (BSA) protein and model bacterial cells. Whole blood adsorption experiments showed that the polySBMA-modified silicon surface exhibited excellent hemocompatibility and effective anti-adhesion to blood cells. Silicon membranes with such antifouling and hemocompatible surfaces can be advantageously used to drastically extend the service life of implantable medical devices such as artificial kidney devices.

MALDI‐TOF Analysis of Halogen Telechelic Poly(methyl methacrylate)s and Poly(methyl acrylate)s Prepared by Atom Transfer Radical Polymerization (ATRP) or Single Electron Transfer‐Living Radical Polymerization (SET‐LRP)

Poly(methyl methacrylate)s (PMMA)s and poly(methyl acrylate)s (PMA)s are prepared by atom transfer radical polymerization (ATRP) or single electron transfer‐living radical polymerization (SET‐LRP) using methyl dichloroacetate (MDCA) and ethyl dibromoacetate (EDBA) as bifunctional initiators. The chain‐end functionality is determined by MALDI‐TOF mass spectrometry. The target PMMA (Mn = 2000 g mol−1) and PMA (Mn = 2000 g mol−1) samples obtained by ATRP of MMA and MA with MDCA as initiator have 12 and 81 mol% bis‐chloro end groups, respectively; those prepared by SET‐LRP have 57 and 100 mol% bis‐chloro end groups, respectively. The PMMAs obtained by ATRP or SET‐LRP with EDBA have no bromine end groups. image

Ready access to end-functional polystyrenes via a combination of ARGET ATRP and thiol–ene chemistry

Bromine end-groups of ATRP polystyrenes were converted into terminal alkene groupsviaa facile synthetic strategy. Subsequently, a light-induced radical thiol–ene reaction was employed for the functionalization of the terminal double bonds.

Structure-directed functional properties of symmetrical and unsymmetrical Br-substituted Schiff-bases

This study deals with the investigation of two low molecular weight Schiff base compounds with bromine end groups, differing only by the presence or absence of one methyl group, with the aim of better understanding the solution and the solid state optical, electrochemical and thermic properties generated by the small structural features. The compounds were structurally characterized by 1H NMR, 13C NMR and FTIR spectroscopies, single-crystal X-ray diffraction and gas chromatography analysis. Their thermal behavior was evidenced by polarized light microscopy and differential scanning calorimetry. The single crystal structure of the compounds reveals the versatility of bromine substituents which can adopt an attractive or repulsive electron effect, driven by the structural environment. A comparison of the structures shows that the introduction of a methyl unit as a bulky group hinders completely the π–π stacking interaction within the structural rows, inducing larger intermolecular distances resulting in quite different functional physical and chemical properties.

The relationship between end‐group concentrations and stability of spin‐coated thin polymer films investigated by ToF‐SIMS depth profiling

Stable and unstable spin‐coated polymer films were prepared using various solvents and substrates. The relationship between polymer end‐group concentrations and stability of spin‐coated polymer films was revealed by time‐of‐flight secondary ion mass spectrometry depth profiling. A high concentration of bromine end groups at the interface between the polymer and the substrate helped to prevent the dewetting of films. In contrast, the bromine end groups were found to be more evenly distributed in unstable thin films. The extent to which the bromine end groups segregate to the interface depended on the competitive interactions between the polymer, the solvent and the substrate. Stronger polymer–solvent and solvent–substrate interactions prevented the segregation of the bromine end groups to the interface, resulting in unstable polymer films. Copyright © 2013 John Wiley & Sons, Ltd.

Steering On-Surface Polymerization with Metal-Directed Template

On-surface polymerization represents a novel bottom-up approach for producing macromolecular structures. To date, however, most of the structures formed using this method exhibit a broad size distribution and are disorderly adsorbed on the surface. Here we demonstrate a strategy of using metal-directed template to control the on-surface polymerization process. We chose a bifunctional compound which contains pyridyl and bromine end groups as the precursor. Linear template afforded by pyridyl-Cu-pyridyl coordination effectively promoted Ullmann coupling of the monomers on a Au(111) surface. Taking advantage of efficient topochemical enhancement owing to the conformation flexibility of the Cu-pyridyl bonds, macromolecular porphyrin structures that exhibit a narrow size distribution were synthesized. We used scanning tunneling microscopy and kinetic Monte Carlo simulation to gain insights into the metal-directed polymerization at the single molecule level. The results reveal that the polymerization process profited from the rich chemistry of Cu which catalyzed the C-C bond formation, controlled the size of the macromolecular products, and organized the macromolecules in a highly ordered manner on the surface.

Silica nanoparticles functionalized via click chemistry and ATRP for enrichment of Pb(II) ion

Silica nanoparticles have been functionalized by click chemistry and atom transfer radical polymerization (ATRP) simultaneously. First, the silanized silica nanoparticles were modified with bromine end group, and then the azide group was grafted onto the surface via covalent coupling. 3-Bromopropyl propiolate was synthesized, and then the synthesized materials were used to react with azide-modified silica nanoparticles via copper-mediated click chemistry and bromine surface-initiated ATRP. Transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis were performed to characterize the functionalized silica nanoparticles. We investigated the enrichment efficiency of bare silica and poly(ethylene glycol) methacrylate (PEGMA)-functionalized silica nanoparticles in Pb(II) aqueous solution. The results demonstrated that PEGMA-functionalized silica nanoparticles can enrich Pb(II) more quickly than pristine silica nanoparticles within 1 h.

Synthesis of mikto-topology star polymer containing one cyclic arm

Well-defined mikto-topology star polystyrene composed of one cyclic arm and four linear arms was synthesized by a combination of atom transfer radical polymerization (ATRP) and Cu-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. First, the bromine-alkyne α,ω-linear polystyrenes containing four hydroxyl groups protected with acetone-based ketal groups were synthesized by ATRP of styrene using a designed initiator. Then, the bromine end-group was converted to the azide and the linear polystyrene was cyclized intra-molecularly by the CuAAC reaction. The four hydroxyl groups were released by deprotection and then esterified with 2-bromoisobutyryl bromide to produce a cyclic polymer bearing four ATRP initiating units. By subsequent ATRP of styrene to grow linear polymers with the cyclic polystyrene as a macroinitiator, the mikto-topology star polymers were prepared. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Synthesis of amphiphilic A2B star-shaped copolymers of polystyrene-b-[poly(ethylene oxide)]2 via atom transfer nitroxide radical coupling

The amphiphilic A2B star-shaped copolymers of polystyrene-b-[poly(ethylene oxide)]2 (PS-b-PEO2) were synthesized via the combination of atom transfer nitroxide radical coupling (ATNRC) with ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP) mechanisms. First, a novel V-shaped 2,2,6,6-tetramethylpiperidine-1-oxyl-PEO2 (TEMPO-PEO2) with a TEMPO group at middle chain was obtained by ROP of ethylene oxdie monomers using 4-(2,3-dihydroxypropoxy)-TEMPO and diphenylmethyl potassium as coinitiator. Then, the linear PS with a bromine end group (PS-Br) was obtained by ATRP of styrene monomers using ethyl 2-bromoisobutyrate as initiator. Finally, the copolymers of PS-b-PEO2 were obtained by ATNRC between the TEMPO and bromide groups on TEMPO-PEO2 and PS-Br, respectively. The structures of target copolymers and their precursors were all well-defined by gel permeation chromatographic and nuclear magnetic resonance (1H NMR). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Synthesis of block copolymers via atom transfer radical polymerization and ‘click chemistry’ grafted from pre-functionalized polypropylene surfaces using gamma irradiation

In this article, we demonstrate a new approach to grafting block copolymers from polypropylene substrates, using gamma irradiation, in the presence of transfer agent (CBr4) and terminator agents (CuBr2 and I2) and monomer. Varying the concentration of CBr4 and CuBr2 exerts control over both the molecular weight of grafted polymers and the surface density of tethered bromine groups. The bromine end-groups were subsequently exploited to reinitiate polymerization from the surface via atom transfer radical polymerization (ATRP), yielding block copolymers and terpolymers. ATR-FTIR, XPS and EDX/SEM were used to confirm the successful synthesis of surface-tethered block copolymers. In a similar approach using I2 as terminator agent, we functionalized PP surfaces with iodine end-functional graft polymers. The presence of iodine was then exploited to grow poly(methyl acrylate) from the surfaces using iodine transfer polymerization. The halogenated (Br), gamma grafted surfaces were then subjected to organic functionalization reactions via two different approaches: (i) azide–alkyne click chemistry and (ii) thio–bromo nucleophilic substitution. The successful click functionalization of grafted-PP was verified using both ATR-FTIR and XPS analyses.

Photoinduced Conjugation of Aldehyde Functional Polymers with Olefins via [2 + 2]-Cycloaddition

Polymer end group modifications via [2 + 2] Paterno–Büchi reactions were carried out. Polyisobornyl acrylate (PiBoA, 3100 g·mol–1) and polystyrene (PS, 2800 g·mol–1) was synthesized by atom transfer radical polymerization (ATRP) employing an aldehyde functional initiator. Good control over the polymerizations was achieved, and material with high aldehyde functionality was obtained. The terminal aldehyde was then reacted with alkenes under UV irradiation in [2 + 2] cycloaddition reactions. Good yields of the modification reaction was confirmed via NMR and by electrospray ionization mass spectrometry (ESI–MS) analysis and generally conversion of the aldehyde function into the respective oxetanes of 90% or higher was observed. With the oxetane, a variety of functional groups were introduced to the polymer chain ranging from multifunctional allyl-compounds to disubstituted alkenes and amino- or hydroxyl-functional alkenes. In the photoreaction, the integrity of the bromine end group of the ATRP polymers is retained. ATRP chain extensions can be performed after the cycloaddition, demonstrating the versatility of this newly introduced polymer modification reaction.

Ambient Temperature Synthesis of Triblock Copolymers via Orthogonal Photochemically and Thermally Induced Modular Conjugation

A strategy for the modular ambient temperature synthesis of ABA and ABC triblock copolymers via a combination of photoinduced Diels–Alder reactions with thermal Diels–Alder reactions and azide–alkyne click chemistry is reported. Polystyrene (PS) and PMMA (PMMA) with α-2,5-dimethylbenzophenone and ω-cyclopentadienyl or ω-azide end-functionality were prepared via atom transfer radical polymerization (ATRP) and subsequent transformation of the bromine end-group. The phototriggered conjugation reaction proceeds via an in situ formation of highly reactive o-quinodimethanes. Maleimide-capped poly(tert-butyl acrylate) obtained via ATRP was employed as dienophile. Alkyne and maleimide functionalized poly(ethylene glycol) (PEG) were synthesized by esterification of monomethoxy PEG. PtBA-b-PMMA-b-PtBA and PtBA-b-PS-b-PtBA were successfully prepared in a one-pot reaction at ambient temperature combining photoinduced and thermal Diels–Alder reactions. ABC triblock copolymers (PtBA-b-PS-b-PEG) with narrow polydispersi...

Diels–Alder Reactions as an Efficient Route to High Purity Cyclic Polymers

A simple and efficient route for the synthesis of cyclic polymer systems is presented. Linear furan protected α-maleimide-ω-cyclopentadienyl functionalized precursors (poly(methyl methacrylate) and poly(tert-butyl acrylate)) were synthesized via atom transfer radical polymerization (ATRP) and subsequent substitution of the bromine end-group with cyclopentadiene. Upon heating at high dilution, deprotection of the dieneophile occurs followed by an intramolecular Diels-Alder reaction yielding a high purity cyclic product.