Surface-initiated Nitroxide-mediated Polymerization Research Articles

High-Capacity Poly(4-vinylpyridine) Grafted PolyHIPE Foams for Efficient Plutonium Separation and Purification.

The use of anion-exchange resins to separate and purify plutonium from various sources represents a major bottleneck in the throughput that can be achieved when this step is part of a larger separation scheme. Slow sorption kinetics and broad elution profiles necessitate long contact times with the resin, and the recovered Pu is relatively dilute, requiring the handling of large volumes of hazardous material. In this work, high internal-phase emulsion (HIPE) foams were prepared with a comonomer containing a dormant nitroxide. Using surface-initiated nitroxide-mediated polymerization, the foam surface was decorated with a brush of poly(4-vinylpyridine), and the resulting materials were tested under controlled flow conditions as anion-exchange media for plutonium separations. It was found that the grafted foams demonstrated greater ion-exchange capacity per unit volume than a commercial resin commonly used for Pu separations and had narrower elution profiles. The ion-exchange sites (quaternized pyridine) were exposed on the surface of the large pores of the foam, resulting in convective mass transfer, the driving force for the excellent separation properties exhibited by the synthesized polyHIPE foams.

Substrate-Independent Approach to Dense Cleavable Polymer Brushes by Nitroxide-Mediated Polymerization.

High grafting density polymer brushes are grown on an inimer coating bearing nitroxide-mediated polymerization (NMP) inimers and glycidyl methacrylate (GMA). The inimer coating is cross-linked on the substrate to provide an initiator layer with needed stability during long exposure to organic solvents at moderate to high temperatures. Surface-initiated nitroxide-mediated polymerization (SI-NMP) is conducted to grow polystyrene (PS) brushes on the coating with a sacrificial layer designed to cleave the brushes. The cleaved brushes have larger molecular weights than the corresponding free polymers. The grafting density of the brushes is as high as 1.12 chains/nm2 throughout the brush growth, which is among the densest PS brushes reported so far. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) depth profiling are used to reveal the surface morphology and kinetics of the growth.

Hierarchically structured, blue-emitting polymer hybrids through surface-initiated nitroxide-mediated polymerization and water templated assembly

A facile and robust approach for fabricating structured, blue-emitting polymer hybrids is explored by grafting poly(styrene) incorporating π-conjugated oligo(fluorene) side-chains, to fluoromica silicate layers through surface-initiated nitroxide-mediated polymerization (SI-NMP). It is expected that the polymer intercalation can effectively reduce π-stacking, chain–chain interactions, twists and bends, and interfacial effects, leading to significant difference in the electronic/optoelectronic properties, and improved optical, thermal and chemical stability of the materials. The experimental results indicate that the bottom-up strategy is rational and efficacious. The hybrids exhibit a blue photoluminescence quantum yield (PL-QY) as high as 0.90, even in the solid, which makes the materials appealing for polymer light-emitting devices (PLEDs). The materials also show significantly enhanced thermal, and chemical stabilities with respect to the organic precursors. If processed under specific controlled conditions, the hybrids spontaneously assemble into highly ordered microporous films, where an organization of matter at different length scales is obtained. Since the introduction of surface patterning in the active layer could enhance the extraction of light generated in the device, this hierarchical organization is a promising tool for the further development of optimized hybrid PLEDs.

Photo-Induced Macromolecular Functionalization of Cellulose via Nitroxide Spin Trapping

Cellulose is the most abundant organic raw material on the planet. Due to its renewability and biodegradability it is currently attracting much interest for the production of biofuels or platform chemicals. In addition, recent applications in the field of materials science have appeared, arising from the low density and the excellent thermal and mechanical properties of cellulose, particularly in the production of composites. However, there are still some major drawbacks to using cellulose including its water-absorbing nature and its poor compatibility with other materials, for example, synthetic polymers. To combat these problems, grafting synthetic polymers onto cellulose is the most straightforward method to alter its surface properties and thus to control the wettability, adhesion, or hydrophobicity of the biopolymer. Although grafting from methods such as surface-initiated nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP),reversible addition–fragmentation transfer polymerization (RAFT), or ring-opening polymerization (ROP)are considered as the most efficient approaches, particularly in terms of grafting density, efficient grafting to methods have recently produced very good results. Cellulose has been successfully modified with preformed polymers by both hetero-Diels–Alderand 1,3-dipolar nitrile imine-ene cycloadditions. In the latter case, light was used as the grafting trigger. Importantly, employing light offers temporal and spatial control of the reaction. In the present contribution, we introduce a very facile grafting to protocol based on the generation of radicals at the surface of cellulose by mild UV irradiation (λmax ∼ 311 nm) of an immobilized photoinitiator, followed by radical trapping with a nitroxide-functionalized polymer (see Scheme 1). Previously, nitroxide radical coupling was employed to efficiently link polymer strands, however via a copper-catalyzed mechanism using ATRP-made polymers to generate reactive radicals. A rather similar philosophy based on spin capturing was reported, employing nitrones that after a first radical reaction generate a nitroxide able to undergo a second radical coupling.

Biofunctional oligoN-isopropylacrylamide brushes on silicon wafer surface

In this study, we report a surface-initiated nitroxide-mediated polymerization (NMP) of N-isopropylacrylamide in the presence of cysteamine (CA) chain transfer agent to fabricate oligoN-isopropylacrylamide (oligoNIPAM) brushes with amine end-groups. The resulting oligomeric brushes were characterized by ellipsometry, grazing angle-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and a contact-angle goniometer to identify the film thickness, surface composition, surface morphology and water contact angles. The oligoNIPAM brushes were then functionalized with biotin units in order to provide selective attachment points for streptavidin proteins. Fluorescence spectroscopy confirmed the successful immobilization of streptavidin molecules on the oligoNIPAM brushes. Finally, it is demonstrated that this fabrication method allows the selective immobilization of streptavidin molecules to brush structures functionalized with biotin units.

Surface-Initiated Nitroxide-Mediated Polymerization from Ordered Mesoporous Silica

This work describes, for the first time, the nitroxide-mediated polymerization (NMP) of styrene initiated from an SG1-based alkoxyamine grafted on both the inner and outer surfaces of ordered mesoporous silica (OMS) particles. The OMS particles with various morphologies were synthesized by sol−gel chemistry in the presence of a surfactant template. The initiator derived from the BlocBuilder alkoxyamine was covalently grafted via a dimethylethoxysilane functional group. The polymerizations were conducted in the presence of a free alkoxyamine with chemical structure similar to that of the grafted one. The monomer conversion was monitored by 1H NMR analysis and the concentration of released nitroxide could be calculated, providing an estimation of the fraction of dead chains. The weight fraction of grafted polymer and the molar mass distributions of the free and grafted chains were determined. From this information, an effect of the OMS particle structure on the outcome of the polymerization could be evaluated.

Synthesis of monodisperse zinc sulfide particles grafted with concentrated polystyrene brush by surface-initiated nitroxide-mediated polymerization

Monodisperse zinc sulfide (ZnS) particles of diameters ranging from 120 to 400 nm were prepared and then coated with a thin layer of silica (SiO 2). After the surface modification with an alkoxyamine derivative, polystyrene (PS) brushes of chain lengths ranging from 30,000 to 114,000 in M n with relatively low polydispersities less than 1.5 in M w/ M n were successfully grafted by surface-initiated nitroxide-mediated polymerization, where the M n and M w are the number- and weight-averaged molecular weights, respectively. The graft density reached a value as high as 0.9 chains nm −2. These core–shell hybrid particles (ZnS@SiO 2–PS) were highly dispersible, without any aggregation, in various solvents good for PS, also forming a monolayer at the air–water interface by spreading its solution. The transmission electron microscopic observation of the monolayers deposited on a solid support revealed two-dimensionally close-packed arrays of particles. These monolayers exhibited a beautiful structural color dependent on the angle of incident light because of such an ordered array of the ZnS cores with a high refractive index. Hollow spheres constituted of a SiO 2 shell with well-defined, high-density PS brushes were first synthesized by selective dissolution of the ZnS core from the ZnS@SiO 2–PS hybrid particle.

Hairy particle‐supported 4‐N,N‐dialkylaminopyridine: An efficient and recyclable nucleophilic organocatalyst

A polymer brush-supported 4-N,N-dialkylaminopyridine catalyst was prepared by surface-initiated nitroxide-mediated polymerization from initiator functionalized crosslinked polystyrene particles. The hairy particles efficiently catalyzed the acylation of secondary alcohols and Baylis-Hillman reaction of 4-nitrobenzaldehyde and methyl vinyl ketone, and were recycled at least six times with no or negligible decrease in the reaction yield.

Surface‐initiated nitroxide‐mediated polymerization: a tool for hybrid inorganic/organic nanocomposites ‘in situ’ synthesis

AbstractHybrid silica particles comprised of an inorganic core and an organic polymer shell can be synthesized by surface‐initiated nitroxide‐mediated polymerization (SINMP) in the presence of a grafted alkoxyamine as initiator. The layer of initiator molecules attached or adsorbed to the particles surface is based on a nitroxide group. The synthesis and characterization of these alkoxyamine structures are briefly described. The grafted initiator particles are studied in order to determine the nature of the anchorage sites and the grafting density. With a stable radical or nitroxide as chain‐growth moderator tethered to the inorganic core, it was demonstrated that the grafting from or to SINMP exhibits a control character with a very low polydispersity and good agreement between theoretical/experimental molecular weights. A comparative review of different alkoxyamines with a bimolecular system based on a grafted azoic initiator in the presence of an acyclic β‐phosphonylated nitroxide called SG1 is also described. Moreover, original methods for the synthesis of alkoxyamine grafted surface by in situ trapping of carbon radicals and some new developments for colored pigments will be reported. These topics could be one of the directions of the field in the next years. Copyright © 2006 Society of Chemical Industry