Initiators For Nitroxide-mediated Polymerization Research Articles

Hydrophilic Poly(naphthalene diimide)‐Based Acceptor–Photosensitizer Dyads: Toward Water‐Processible Modular Photoredox‐Active Architectures

Hydrophilic naphthalene diimide based acceptor polymers are prepared by the incorporation of triethylene glycol or poly(ethylene glycol) side chains in the monomers and subsequent nitroxide‐mediated polymerization (NMP). The kinetic investigation of the polymerization reveals a controlled chain growth as well as a narrow molar mass distribution. Due to the utilization of a functional NMP initiator, a single Ru(II) photosensitizer unit is readily attached at the polymers chain terminus by a modular approach to construct water soluble photoredox‐active acceptor–photosensitizer dyads. The analysis of the optical properties by steady‐state absorption and emission spectroscopy reveals preserved optical absorption properties of the individual building blocks, and, more importantly, an efficient quenching of the Ru(II) emission assigned to intramolecular charge transfer from the complex to the acceptor polymer. The results demonstrate the versatility of side chain modifications to prepare water‐processible photoredox‐active architectures under preservation of the modular character known from hydrophobic systems. image

MAMA-SG1 initiated nitroxide mediated polymerization of styrene: From Arrhenius parameters to model-based design

Activation and deactivation Arrhenius parameters are estimated for nitroxide mediated polymerization (NMP) of styrene initiated by BlocBuilder MA, based on an extensive set of experimental data covering a broad range of polymerization temperatures (90–120°C) and initial molar ratios of monomer to NMP initiator (100–1000). Data regression analysis is limited to conversions below 0.65 to avoid the possible influence of diffusional limitations on the activation/deactivation process. The applied kinetic model accounts for thermal initiation, chain transfer reactions and diffusional limitations on termination. A distinction is made between (de)activation of NMP initiator and macrospecies. The activation energy for the activation of the NMP initiator is 43±3.5kJmol−1 lower than the one for the dormant macrospecies. At 120°C, the activation rate coefficients amount respectively to 1.18×10−1s−1 and 7.08×10−3s−1, indicative of a fast NMP initiation. Using the obtained parameter estimates, a visualization of ca. 750 polymer chains is performed via advanced kinetic Monte Carlo simulations, explicitly specifying, for the first time, according to the living nature, and chain initiation and dead polymer mechanism. At 120°C, chain transfer to dimer lowers the level of control over chain length and end-group functionality. Model-based optimization reveals the beneficial effect of the use of a stepwise temperature program, as confirmed experimentally via a lowering of the dispersity from a conversion of 0.3 on due to a suppression of thermal initiation and chain transfer to dimer.

ChemInform Abstract: Labile Alkoxyamines: Past, Present, and Future

AbstractReview: 88 refs.

A Homotelechelic bis-terpyridine macroligand: One-step synthesis and its metallo-supramolecular self-assembly

A homotelechelic macroligand bearing two 2,2′:6′,2″-terpyridin-4′-yl units, as chain ends, is used as building block for the preparation of a linear metallo-supramolecular chain-extended polymer. The macroligand has been prepared by nitroxide-mediated polymerization (NMP) of styrene using a bis-terpyridine-functionalized NMP initiator. The controlled character of the NMP process has been confirmed by detailed characterization of the polymer by size-exclusion chromatography, nuclear magnetic resonance spectroscopy as well as mass spectrometry. Subsequently, the self-assembly with FeII ions into the chain-extended metallopolymer and the disassembly thereof, in the presence of a strong competitive ligand, has been studied by UV–vis absorption spectroscopy and diffusion-ordered NMR spectroscopy. The reversibility of the formation of the metallo-supramolecular material, when addressed by external stimuli, could be proven. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Nitroxide-Mediated Polymerization of Methyl Methacrylate and Styrene with New Alkoxyamines from 4-Nitrophenyl 2-Methylpropionat-2-yl Radicals

The N-phenylalkoxyamine N-(1-methyl-(1-(4-nitrophenoxy)carbonyl)ethoxy)-N-(1-methyl-(1-(4-nitrophenoxy)carbonyl)ethyl)benzenamine (1) was prepared by the addition of 4-nitrophenyl 2-methylpropionat-2-yl radicals across the double bond of nitrosobenzene and evaluated as an initiator for nitroxide-mediated polymerization (NMP). N-Phenylalkoxyamines have not been extensively studied in NMP, though they have shown promise in controlling methyl methacrylate (MMA) polymerization to moderate conversions. It is thought that delocalization of the nitroxide radical through the N-phenyl substituent may minimize cross-disproportionation of the nitroxide with the chain end that has made NMP of MMA difficult. Here, we show that alkoxyamine 1 is capable of controlling the NMP of MMA to 50% conversion while maintaining narrow molecular weight distributions (Mw/Mn = 1.12−1.30). Additionally, chain extension from the resulting PMMA macroinitiators with MMA or styrene allows the formation of diblock copolymers. The correspo...

SG1-Functionalized Peptides as Precursors for Polymer−Peptide Conjugates: A Straightforward Approach

We report here a straightforward route to polymer−peptide conjugates via the convenient synthesis of SG1-functionalized peptides able to initiate nitroxide-mediated polymerization (NMP). The NMP initiator SG1-functionalized peptide (SG1-GGGWIKVAV) was prepared by solid-phase peptide synthesis (SPPS) using an automated synthesizer, with a last step consisting of reaction between the carboxylic acid function of the MAMA-SG1 (BlocBuilder) alkoxyamine with the peptide terminal amine in the presence of benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (PyBOP) as coupling agent. The resulting SG1-functionalized resin-attached peptide was used to perform the controlled NMP of styrene, leading after trifluoroacetic acid cleavage to the corresponding polystyrene−peptide conjugate. The latter was thoroughly characterized by UV spectrometry, gel permeation chromatography (GPC), 1H NMR, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).

Noncovalently Connected Micelles, Nanoparticles, and Metal-Functionalized Nanocages Using Supramolecular Self-Assembly

An SCS "pincer"-based nitroxide-mediated polymerization (NMP) initiator has been synthesized and utilized to polymerize tert-butyl acrylate ( ( t )BuA), affording polymers with control over molecular weight and polydispersity. (1)H NMR spectroscopy indicates that the sulfur end group remains intact after deprotection of the P ( t )BuA segment to yield a poly(acrylic acid) segment. The hydrophilic polymer-tethered SCS ligand has been demonstrated to bind to palladium(II), as characterized by a distinctive Pd-C shift in the (13)C NMR spectrum and a diagnostic metal-to-ligand charge-transfer band in the UV-vis spectrum. A pyridine-functionalized NMP initiator has also been synthesized and used to initiate the NMP of styrene with good control and end group fidelity. The binding of these two chain end ligand-functionalized polymers to form an amphiphilic metallosupramolecular diblock copolymer is facile, as indicated through extended (1)H and (13)C NMR studies. The self-assembly of this diblock into well-defined, monodisperse, noncovalently connected micelles (NCCMs) is reported and has been characterized by dynamic light scattering, transmission electron microscopy, and atomic force microscopy. The NCCMs were selectively stabilized throughout the shell layer to produce stable noncovalently connected nanoparticles, resulting in a distinctive reduction in the solution hydrodynamic radius and zeta potential compared to those of the precursor micelle. The hydrophobic core domain was then readily removed via dialysis at low pH to afford a hollow polymeric nanocage with well-defined interior functionality. A significant increase in the solution hydrodynamic radius and shape by AFM analysis was observed upon removal of the core, and the hydrophilic nanocages were shown to be ineffective in the sequestration of hydrophobic dye molecules relative to the parent nanoparticle.

Intermolecular radical addition of alkoxyamines onto olefins: An easy access to advanced macromolecular architectures precursors

Novel “second generation” alkoxyamines, derived from N-(2-methylpropyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (so-called SG1) as initiators for nitroxide-mediated polymerization (NMP) were synthesized by intermolecular radical 1,2-addition (IRA) of a high dissociation rate constant alkoxyamine (BlocBuilder®, also called MAMA-SG1) onto various activated olefins, such as n-butyl acrylate, acrylic acid, dimethylacrylamide, 2-hydroxyethylacrylate and styrene. The potential of this radical addition was further applied to the synthesis of multifunctional alkoxyamines as precursors for complex macromolecular architectures, namely 3- and 4-arm star polymers. For this, tri- and tetra-acrylates were synthesized by reaction of acryloyl chloride with the 1,1,1-tris(hydroxymethyl)ethane and pentaerythritol, respectively, in the presence of triethylamine. The addition of MAMA-SG1 onto these olefins led to the tri- and tetra-functional SG1-based alkoxyamines which were further used to prepare polystyrene stars of controlled molecular weights and polydispersity values not exceeding 2. The individual arms were recovered by hydrolysis of the ester groups of the star core originating from the alkoxyamine initiator under basic conditions. The decreasing molecular weight determined by GPC during hydrolysis demonstrated the star architecture of the polymers.

Covalent attachment of polystyrene on multi-walled carbon nanotubes via nitroxide mediated polymerization

A new method to attach polymers on carbon nanotubes has been studied. We used nitroxide mediated polymerization (NMP) to graft polystyrene from multi-walled carbon nanotubes (MWNTs). Carboxyl groups on MWNTs were activated with thionyl chloride (SOCl2) to give acyl chloride derivative (MWNT-COCl). NMP initiator was introduced to MWNT by esterification of 1-hydroxy-2-phenyl-2-(2′,2′, 6′, 6′-tetramethyl-1′-piperidinyloxy)ethane (HO-PE-TEMPO) with acyl chloride groups of MWNTs. The obtained MWNT-PE-TEMPO was used for initiation of bulk polymerization of styrene, yielding polystyrene-grafted MWNTs (MWNT-g-pSt). The resulting composites of MWNT-g-pSt were analyzed by TEM, SEM, FT-IR and TGA.