Well-controlled Atom Transfer Radical Polymerization Research Articles

Designing Microparticle-Impregnated Polyelectrolyte Composite: The Combination of ATRP, Fast Azidation, and Click Reaction Using a Single-Catalyst, Single-Pot Strategy.

Polystyrene microparticles were covalently impregnated into the networks of functional polyelectrolyte chains designed via a tandem run of three reactions: (i) synthesis of water-soluble polyelectrolyte, (ii) fast azidation and (iii) a ‘click’ reaction, using the single-catalyst, single-pot strategy at room temperature in mild aqueous media. The model polyelectrolyte sodium polystyrenesulfonate (NaPSS) was synthesized via the well-controlled atom transfer radical polymerization (ATRP) whose halogen living-end was transformed to azide and subsequently coupled with an alkyne carboxylic acid through a ‘click’ reaction using the same ATRP catalyst, throughout. Halogen to azide transformation was fast and followed the radical pathway, which was explained through a plausible mechanism. Finally, the success of microparticle impregnation into the NaPSS network was evaluated through Kaiser assay and imaging. This versatile synthetic procedure, having a reduced number of discrete reaction steps and eliminated intermediate work-ups, has established a fast and simple pathway to design functional polymers required to fabricate stable polymer-particle composites where the particles are impregnated covalently and controllably.

Detection of site-dependent segmental mobility of polymer by fluorescent defocused imaging

Polymer chain ends play an important role in the glassy dynamics of polymeric materials. In this study, a combination of single molecule defocus fluorescence microscopy and well-controlled atom transfer radical polymerization was used to investigate site-dependent segmental mobility of poly(n-butyl methacrylate). As the temperature increased, the rotation of fluorophores, which were selectively labelled in chain end and chain middle, was gradually activated. The power spectra of rotation trajectories, the distribution of angular displacement as well as the population of rotating fluorophores demonstrated that the local dynamics was more activated at the chain ends than the middles, showing the unique contribution of the chain end to the dynamics of the system.

The Effects of Salt Type and Salt Concentration on the Performance of Magnetically Activated Nanofiltration Membranes

The effects of salt ion type and salt concentration on flux and rejection improvement of magnetically activated micromixer nanofiltration membranes were investigated. Polymers with varying chain length and chain density were grafted on the NF270 membranes using the well-controlled atom transfer radical polymerization reaction. Superparamagnetic nanoparticles that respond to an oscillating magnetic field were conjugated at the polymer chain ends. The effects of micromixing on breaking the concentration polarization boundary layer were investigated by determining the percentage improvement in flux and rejection in the presence of an external oscillating field. Systematic trends on the salt ion size and feed concentration as well as grafting degrees were observed. The magnetically activated micromixers are more effective in breaking down severer concentration polarization when the charge and concentration of the salt ions are higher. In addition, higher density and longer polymer chains induce stronger micro...

Well-controlled ATRP of 2-(2-(2-Azidoethyoxy)ethoxy)ethyl Methacrylate for High-density Click Functionalization of Polymers and Metallic Substrates.

The combination of atom transfer radical polymerization (ATRP) and click chemistry has created unprecedented opportunities for controlled syntheses of functional polymers. ATRP of azido-bearing methacrylate monomers (e.g. 2-(2-(2-azidoethyoxy)ethoxy)ethyl methacrylate, AzTEGMA), however, proceeded with poor control at commonly adopted temperature of 50 °C, resulting in significant side reactions. By lowering reaction temperature and monomer concentrations, well-defined pAzTEGMA with significantly reduced polydispersity were prepared within a reasonable timeframe. Upon subsequent functionalization of the side chains of pAzTEGMA via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry, functional polymers with number-average molecular weights (Mn) up to 22 kDa with narrow polydispersity (PDI < 1.30) were obtained. Applying the optimized polymerization condition, we also grafted pAzTEGMA brushes from Ti6Al4 substrates by surface-initiated ATRP (SI-ATRP), and effectively functionalized the azide-terminated side chains with hydrophobic and hydrophilic alkynes by CuAAC. The well-controlled ATRP of azido-bearing methacrylates and subsequent facile high-density functionalization of the side chains of the polymethacrylates via CuAAC offers a useful tool for engineering functional polymers or surfaces for diverse applications.

Neue aromatische Bisguanidin-Kupfer-Komplexe und ihre Anwendung in der ATRP / New Aromatic Bisguanidine Copper Complexes and Their Application in ATRP

We synthesized and structurally characterized two new copper(II) monochelate complexes with the ligand 2,2'-(1,2-phenylenebis(1,1,3,3-tetramethyl)guanidine) (TMG2b), [Cu(TMG2b)Cl2] and [Cu(TMG2b)Br2]. Single-crystal structure determination has shown that the complexes [Cu(TMG2b)Cl2] and [Cu(TMG2b)Br2] both crystallize in the orthorhombic space group Pbcn. The copper atoms in all complex cations reside in a coordination environment between tetrahedral and square-planar geometry. Furthermore, the application of the copper complexes with TMG2b as ligand in atom transfer radical polymerization (ATRP) was investigated with styrene as monomer. This study has shown a controlled polymerization process with moderate conversions, but excellent molecular weight distributions that are evidence of a well-controlled ATRP. However, small changes in the ligand structure can have a high impact, and therefore process optimizations and ligand tuning are necessary to develop highly active catalysts for ATRP.

Well‐Defined Iron Complexes as Efficient Catalysts for “Green” Atom‐Transfer Radical Polymerization of Styrene, Methyl Methacrylate, and Butyl Acrylate with Low Catalyst Loadings and Catalyst Recycling

Environmentally friendly iron(II) catalysts for atom-transfer radical polymerization (ATRP) were synthesized by careful selection of the nitrogen substituents of N,N,N-trialkylated-1,4,9-triazacyclononane (R3 TACN) ligands. Two types of structures were confirmed by crystallography: "[(R3 TACN)FeX2 ]" complexes with relatively small R groups have ionic and dinuclear structures including a [(R3 TACN)Fe(μ-X)3 Fe(R3 TACN)](+) moiety, whereas those with more bulky R groups are neutral and mononuclear. The twelve [(R3 TACN)FeX2 ]n complexes that were synthesized were subjected to bulk ATRP of styrene, methyl methacrylate (MMA), and butyl acrylate (BA). Among the iron complexes examined, [{(cyclopentyl)3 TACN}FeBr2 ] (4 b) was the best catalyst for the well-controlled ATRP of all three monomers. This species allowed easy catalyst separation and recycling, a lowering of the catalyst concentration needed for the reaction, and the absence of additional reducing reagents. The lowest catalyst loading was accomplished in the ATRP of MMA with 4 b (59 ppm of Fe based on the charged monomer). Catalyst recycling in ATRP with low catalyst loadings was also successful. The ATRP of styrene with 4 b (117 ppm Fe atom) was followed by precipitation from methanol to give polystyrene that contained residual iron below the calculated detection limit (0.28 ppm). Mechanisms that involve equilibria between the multinuclear and mononuclear species were also examined.

Atom transfer radical polymerization (ATRP) of methyl methacrylate mediated by iron(II) chloride in the presence of polyethers as both solvents and ligands

Iron(II) chloride in combination with various polyethers form the homogeneous, “green” catalytic mixtures that are capable of promoting the well-controlled atom transfer radical polymerization of methyl methacrylate in the absence of any additional ligands or solvents. With poly(ethylene glycol)s, linear semilogarithmic plots of conversion vs. time and of molecular weight vs. monomer conversion were obtained with polydispersities as low as 1.32. The effects of the polyether structure, molecular weight, and chain-end functionality on the polymerization kinetics were also investigated.

Macromol. Theory Simul. 9/2011

Cover: Using the thermodynamics of the atom transfer radical polymerization (ATRP) equilibrium as the basis of the kinetic modeling of ATRP, a linear correlation between the maximum ATRP equilibrium constant for controlled polymerization and the propagation rate constant is described. This enables the design of well-controlled ATRP systems. Further details can be found in the article by H. Bergenudd,* M. Jonsson, and E. Malmström on page 814.

Facile di-color emission tuning of poly[1-(4-vinylstyryl)naphthalene] with naphthalimide end group via ATRP

A series of fluorescent polymers with tunable di-color emission, P(NVS) n –NAPHs, were prepared via well-controlled atom transfer radical polymerization (ATRP). Each of the obtained polymers with different molecular weights has a composite emission spectrum comprising a blue component originated from the monomer, 1-(4-vinylstyryl)naphthalene (NVS), and a green component originated from the initiator, 2-(2,3-dihydro-2-(4-methoxyphenyl)-1,3-dioxo-1 H-phenalen-7-ylamino)-ethyl-2-chloroacetate (NAPH). The intensity of the blue and green emission bands can be easily tuned by changing the polymer chain length. The blue emission part is enhanced with increasing the molecular weight of the fluorescent polymer in both DMF solution and film state.