Air‐tolerantly surface‐initiated AGET ATRP mediated by iron catalyst from silica nanoparticles

Well‐defined polymer‐nanoparticle hybrids were prepared by a newly reported method: atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) mediated by iron catalyst. The kinetics of the surface‐initiated AGET ATRP of methyl methacrylate from the silica nanoparticles, which was mediated by FeCl₃/triphenylphosphine as a catalyst complex, ascorbic acid as a reducing agent, N,N‐dimethylformamide as the solvent in the presence of a “sacrificial” (free) initiator, was studied. Both the free and grafted polymers were grown in a control manner. The chemical composition of the nanocomposites was characterized by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and ¹H nuclear magnetic resonance spectroscopy. Thermogravimetric analysis was used to estimate the content of the grafted organic compound, and transmission electron micrographs was used to observe the core‐shell structure of the hybrid nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2006–2015, 2010     

Diblock and triblock copolymers of styrene and acetoxymethylstyrene by one‐pot ATRP

We describe the synthesis of diblock and triblock copolymers by sequential atom transfer radical polymerization of styrene and acetoxymethylstyrene. Contrary to the usual block copolymerization involving isolation of the macroinitiator, a convenient one‐pot procedure is developed. This is possible because of the preferential polymerization of acetoxymethylstyrene, even in the presence of residual styrene, as inferred from characterization of the intermediate polystyrenes and the block copolymers by size exclusion chromatography, ¹H NMR, Fourier transform infrared spectroscopy, differential scanning calorimetry, and GPEC techniques. The latent acetoxy functionalities in these block copolymers are shown to be easily unmasked to ? OH and ? Br functionalities, with the potential for block ionomers and dense graft architectures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 575–583, 2005     

Novel superhydrophobic silica/poly(siloxane‐fluoroacrylate) hybrid nanoparticles prepared via two‐step surface‐initiated ATRP: Synthesis,characterization, and wettability

Poly(siloxane‐fluoroacrylate)‐grafted silica hybrid nanoparticles were prepared by surface‐initiated atom transfer radical polymerization (SI‐ATRP). The silica nanoparticles with α‐bromo‐ester initiator group for copper‐mediated ATRP were prepared by the self‐assembled monolayers of (3‐aminopropyl)triethoxysilane and 2‐bromoisobutyrate bromide. Well‐defined diblock copolymer brushes consisting of poly(methacryloxypropyltrimethoxysilane) and poly(2,2,3,3,4,4,4‐heptafluorobutyl methacrylate) blocks were obtained by using initial homopolymer brushes as the macroinitiators for the SI‐ATRP of the second monomer. Chemical compositions and structures of the nanoparticles were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography. Surface properties and morphology of the nanoparticles were investigated with X‐ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and water contact angle measurement. It is revealed that the surfaces of the nanocomposites are rough at the microscale and nanoscale. The formation reason of the superhydrophobic surfaces was also discussed in this work. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Novel superhydrophobic silica/poly(siloxane‐fluoroacrylate) hybrid nanoparticles prepared via surface‐initiated ATRP and their surface properties: The effects of polymerization conditions

A series of superhydrophobic poly(methacryloxypropyltrimethoxysilane, MPTS‐b‐2,‐2,3,3,4,4,4‐heptafluorobutyl methacrylate, HFBMA)‐grafted silica hybrid nanoparticles (SiO₂/PMPTS‐b‐PHFBMA) were prepared by two‐step surface‐initiated atom transfer radical polymerization (SI‐ATRP). Under the adopted polymerization conditions in our previous work, the superhydrophobic property was found to depend on the SI‐ATRP conditions of HFBMA. As a series of work, in this present study, the effects of polymerization conditions, such as the initiator concentration, the molar ratio of monomer and initiator, and the polymerization temperature on the SI‐ATRP kinetics and the interrelation between the kinetics and the surface properties of the nanoparticles were investigated. The results showed that the SI‐ATRP of HFBMA was well controlled. The results also showed that both the surface microphase separation and roughness of the hybrid nanoparticles could be strengthened with the increase of the molecular weight of polymer‐grafted silica hybrid nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

1,3‐dichlorotetra‐n‐butyldistannoxane as a novel ATRP initiator: Property,catalysis ability,and mechanism

1,3‐dichloro‐tetra‐n‐butyl‐distannoxane, which contains Sn? Cl bonds, was used as a novel initiator for atom transfer radical polymerization of styrene in bulk. Some interesting results that were thought to be related to the characteristics of the 1,3‐dihalotetra‐alkyl‐distannoxanes had been obtained. The concentration of the 1,3‐dichlorotetra‐n‐butyl‐distannoxane in the bulk solution of styrene was confirmed to be an important factor for the different results of the polymerization. The corrected theoretical molecular weights, which were based on the proposed mechanism, accorded with the GPC results very well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 942–948, 2007     

Diselenocarbamates,novel initiators in ATRP of styrene

The atom transfer radical polymerizations (ATRPs) of styrene initiated by diselenocarbamates were carried out for the first time. The polymerization showed first‐order kinetic with respect to the monomer concentration, and the molecular weights of the obtained polymers increased linearly with the monomer conversions with narrow molecular weight distributions (as low as 1.16). The results of chain extension, ¹H NMR, UV–vis, and MALDI‐TOF MS confirmed that the resultant polystyrene possessed some degree of living diselenocarbamates terminal. However, significant amounts of dead polymers (about 53%) were also found. This work offered an alternative type of ATRP initiator, and the seleno‐terminated polymers may be useful in biotechnological and biomedical applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1927–1933     

Tailor‐made hybrid nanostructure of poly(ethyl acrylate)/clay by surface‐initiated atom transfer radical polymerization

Hybrid nanoarchitecture of tailor‐made Poly(ethyl acrylate)/clay was prepared by surface‐initiated atom transfer radical polymerization (SI‐ATRP), by tethering ATRP initiator on active hydroxyl group, present in surface as well as in the organic modifier of the clay used. Extensive exfoliation was facilitated by using these initiator modified clay platelets. Poly(ethyl acrylate) chains with controlled polymerization and narrow polydispersities were forced to be grown from within the clay gallery (intergallery) as well as from the outer surface (extragallery) of the clay platelets. The polymer chains attached onto clay surfaces might have the potential to provide the composites with enhanced compatibility in blends with common polymers. Attachment of the initiator on clay platelets was confirmed by Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), elemental analysis, Wide‐angle X‐ray diffraction (WAXD), and microscopic analysis. Finally, end group analysis (by Matrix‐Assisted Laser Desorption Ionization Mass Spectrometry, and chain extension experiment) of the cleaved polymer and morphological study (by WAXD, Transmission Electron Microscopy), performed on the polymer grafted clays examined the effect of grafting on the efficiency of polymerization and the degree of dispersion of clay tactoids in polymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5014–5027, 2008     

Construction of hydroxyl‐terminated poly(N‐isopropylacrylamide) brushes on silicon wafer via surface‐initiated atom transfer radical polymerization

Surface‐initiated atom transfer radical polymerization (SI‐ATRP) of N‐isopropylacrylamide (NIPAM) on silicon wafer in the presence of 2‐mercaptoethanol (ME) chain transfer agent was conducted in attempt to create controllable hydroxyl‐terminated brushes. The initiator‐immobilized substrate, was prepared by the esterification of hydroxyl groups on silicon wafer with 2‐bromopropionyl bromide (2‐BPB); followed by the ATRP of NIPAM using a catalyst system, that is, Cu(I)Br/2,2′‐bipyridine (2,2′‐bpy) and a chain transfer agent, that is, ME. The formation of homogeneous tethered poly(N‐isopropylacrylamide) (poly(NIPAM) brushes with hydroxyl end‐group, whose thickness can be tuned by chancing ME concentration, is evidenced by using the combination of grazing angle attenuated total reflectance‐Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, ellipsometry, atomic force microscopy, gel permeation chromatography, and water contact‐angle measurements. The calculation of grafting parameters from experimental measurements indicated the synthesis of densely grafted poly(NIPAM) films with hydroxyl end‐group on silicon wafer and allowed us to predict a ME concentration for forming a “brush” conformation for the chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3880–3887, 2010     

Properties of covalently bonded layered‐silicate/polystyrene nanocomposites synthesized via atom transfer radical polymerization

Covalently bonded layered silicated/polystyrene nanocomposites were synthesized via atom transfer radical polymerization in the presence of initiator‐modified layered silicate. The resulting nanocomposites had an intercalated and partially exfoliated structure, as confirmed by X‐ray diffraction and transmission electron microscopy. The thermal properties of the nanocomposites improved substantially over those of neat polystyrene. In particular, a maximum increase of 35.5 °C in the degradation temperature was displayed by these nanocomposites. Additionally, the surface elastic modulus and hardness of these nanocomposites were more than double those of pure polystyrene. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 534–542, 2005     

Kinetics of surface‐initiated atom transfer radical polymerization

Although atom transfer radical polymerization (ATRP) is often a controlled/living process, the growth rate of polymer films during surface‐initiated ATRP frequently decreases with time. This article investigates the mechanism behind the termination of film growth. Studies of methyl methacrylate and methyl acrylate polymerization with a Cu/tris[2‐(dimethylamino)ethyl]amine catalyst system show a constant but slow growth rate at low catalyst concentrations and rapid growth followed by early termination at higher catalyst concentrations. For a given polymerization time, there is, therefore, an optimum intermediate catalyst concentration for achieving maximum film thickness. Simulations of polymerization that consider activation, deactivation, and termination show trends similar to those of the experimental data, and the addition of Cu(II) to polymerization solutions results in a more constant rate of film growth by decreasing the concentration of radicals on the surface. Taken together, these studies suggest that at high concentrations of radicals, termination of polymerization by radical recombination limits film growth. Interestingly, stirring of polymerization solutions decreases film thickness in some cases, presumably because chain motion facilitates radical recombination. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 386–394, 2003     

Kinetic studies of surface‐initiated atom transfer radical polymerization in the synthesis of magnetic fluids

We present results from kinetic studies on the surface‐initiated atom transfer radical polymerization in the preparation of polymer brush‐coated magnetic particles from a heterogeneous system. It is shown that a controlled reaction behavior and a reproducible surface functionalization with end‐tethered polymers are achieved, although the reaction advances gradually from a biphasic solid–liquid mixture to a stable colloidal dispersion of the nanoobjects. Although the initiator‐functional magnetite nanoparticles initially form a precipitate, the formation of a polymer layer on the particle surface in the course of the reaction contributes to a sterical stabilization in dispersion. We thoroughly investigated the development of the initial heterogeneous system with time and in various concentration regimes by simultaneously monitoring the monomer conversion, molar mass, the hydrodynamic diameter of the nanoobjects, and the magnetite content of the dispersions at different reaction times. The results indicate first‐order chain growth kinetics with respect to the monomer and narrow molar mass distributions, demonstrating good control on the particle architecture. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Fluorinated bio‐acceptable polymers via an ATRP macroinitiator approach

Polymers derived from bio‐acceptable poly(methyl methacrylate) (PMMA), poly(2‐methoxyethyl acrylate) (PMEA), and poly(oligo(ethylene glycol) methyl ether methacrylate) (PPEGMA) have been prepared via atom transfer radical polymerization (ATRP) utilizing an initiator prepared from a fluoroalkoxy‐terminated oligoethylene glycol. Polymerizations are controlled as seen by both linear first‐order kinetics and molecular weight evolution coupled with low polydispersities (<1.25) with respect to conversion. A range of ligands have been used depending upon the nature of the monomer: N‐(n‐propyl)‐2‐pyridyl‐methanimine with the methacrylates MMA and PEGMA and 1,1,4,7,10,10‐hexamethyltriethylene tetramine (HMTETA) with MEA. In all cases the use of the fluorinated initiator results in a lower apparent rate of propagation (k_p^app) as compared with the more conventional and nonfluorinated initiator, ethyl 2‐bromoisobutyrate. The initiator generally also serves as an internal plasticizer lowering the glass transition temperature from the parent polymers. The surface characteristics of the fluoroinitiator containing polymers are altered compared with the nonfluorinated analogues. This is reflected in a significant increase in the advancing water contact angles of all fluoro‐containing polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5770–5780, 2007     

Probing the effects of π–π stacking on the controlled radical polymerization of styrene and fluorinated styrene

The addition of the π–π stacking agent octafluorotoluene (OFT) resulted in up to a 50% reduction in monomer conversion after 24 h for atom transfer radical polymerization (ATRP) reactions of styrene, when performed at 85 °C with 1 eq of OFT compared with styrene in the initial reaction mixture. Monitoring the progress showed that the ATRP of styrene in the presence of either OFT or hexafluorobenzene (HFB) maintained a linear relationship between monomer conversion and number average molecular weights, while showing a first order rate dependence on monomer. The effects of π–π stacking on the K_ATRP could be overcome by using adjusting the redox activity of the metal‐ligand complex while maintaining reaction temperatures of 85 °C. Further experiments showed that nitroxide‐mediated polymerizations of St were affected to an identical extent by the presence of the π–π stacking agent HFB. The ATRP of pentafluorostyrene (PFSt) in the presence of π–π stackers benzene or toluene showed an increase in monomer conversion compared with reactions in their absence, consistent with M_n π–π stacking increasing the stability of the active radical. Interactions between the π–π stacking agents OFT and HFB and the aromatic groups in the ATRP of St or PFSt were verified by ¹H NMR analysis. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Covalent polymeric modification of graphene nanosheets via surface‐initiated single‐electron‐transfer living radical polymerization

Graphene nanosheets offer intriguing electronic, thermal, and mechanical properties and are expected to find a variety of applications in high‐performance nanocomposite materials. Dispersal of graphene nanosheets in polymer hosts and precise interface control are challenging due to their strong interlayer cohesive energy and surface inertia. Here, an efficient strategy is presented for growing polymers directly from the surface of reduced graphene oxide (GO). This method involves the covalent attachment of Br‐containing initiating groups onto the surface of hydrazine hydrate reduced GO via a diazonium addition and the succeeding linking of poly(tert‐butyl methacrylate) (PtBMA) chains (71.7 wt % grafting efficiency) via surface‐initiated single‐electron‐transfer living radical polymerization (SET‐LRP) to graphene nanosheets. The resulting materials were characterized by using a range of testing techniques and it was proved that polymer chains were successfully introduced to the surface of exfoliated graphene sheets. After grafting with PtBMA, the modified graphene sheets still maintained the separated single layers, and the dispersibility was improved significantly. The method is believed to offer possibilities for optimizing the processing properties and interface structure of graphene–polymer nanocomposites. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

One‐step synthesis of hyperbranched polyethylene macroinitiator and its block copolymers with methyl methacrylate or styrene via ATRP

Block copolymers of hyperbranched polyethylene (PE) and linear polystyrene (PS) or poly(methyl methacrylate) (PMMA) were synthesized via atom transfer radical polymerization (ATRP) with hyperbranched PE macroinitiators. The PE macroinitiators were synthesized through a “living” polymerization of ethylene catalyzed with a Pd‐diimine catalyst and end‐capped with 4‐chloromethyl styrene as a chain quenching agent in one step. The macroinitiator and block copolymer samples were characterized by gel permeation chromatography, ¹H and ¹³C NMR, and differential scanning calorimetry. The hyperbranched PE chains had narrow molecular weight distribution and contained a single terminal benzyl chloride per chain. Both hyperbranched PE and linear PS or PMMA blocks had well‐controlled molecular weights. Slow initiation was observed in ATRP because of steric effect of hyperbranched structures, resulting in slightly broad polydispersity index in the block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3024–3032, 2010     

Preparation of polymer‐grafted carbon black nanoparticles by surface‐initiated atom transfer radical polymerization

Pristine carbon black was oxidized with nitric acid to produce carboxyl group, and then the carboxyl group was consecutively treated with thionyl chloride and glycol to introduce hydroxyl group. The hydroxyl group on the carbon black surface was reacted with 2‐bromo‐2‐methylpropionyl bromide to anchor atom transfer radical polymerization (ATRP) initiator. The ATRP initiator on carbon black surface was verified by TGA, FTIR, EDS, and elemental analysis. Then, poly (methyl methacrylate) and polystyrene chains were respectively, grown from carbon black surface by surface‐initiated atom transfer radical polymerization (SI‐ATRP) using CuCl/2,2‐dipyridyl (bpy) as the catalyst/ligand combination at 110 °C in anisole. ¹H NMR, TGA, TEM, AFM, DSC, and DLS were used to systemically characterize the polymer‐grafted carbon black nanoparticles. Dispersion experiments showed that the grafted carbon black nanoparticles had good solubilities in organic solvents such as THF, chloroform, dichloromethane, DMF, etc. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3451–3459, 2007     

Low‐Temperature Growth of Thick Polystyrene Brushes via ATRP

Summary: This contribution describes the graft polymerization of polystyrene (PS) by atom transfer radical polymerization at 50, 60, and 75 °C. Thick PS brushes were grown from initiator‐functionalized PGMA layers on silicon, and constant growth rates provide indirect evidence that the polymerizations were controlled.

Formation of polystyrene brushes at T < T_g by ATRP of styrene from α‐bromoester initiator‐functionalized poly(glycidyl methacrylate) layers.     

One‐Reactant Photografting of ATRP Initiators for Surface‐Initiated Polymerization

Self‐initiated photografting polymerization is used to couple the polymerizable initiator monomer 2‐(2‐chloropropanoyloxy)ethyl acrylate to a range of polymeric substrates. The technique requires only UV light to couple the initiator to surfaces. The initiator surface density can be varied by inclusion of a diluent monomer or via selection of initiator and irradiation parameters. The functionality of the initiator surface is demonstrated by subsequent surface‐initiated atom transfer radical polymerization. Surfaces are characterized by x‐ray photoelectron spectroscopy (XPS), ellipsometry, and atomic force microscopy (AFM), and UV‐induced changes to the initiator are assessed by ¹H NMR and gel permeation chromatography (GPC). This is the first time this one‐reactant one‐step technique has been demonstrated for creating an initiator surface of variable density.

     

Preparation of well-defined polystyrene/silica hybrid nanoparticles by ATRP

Immobilization of the atom transfer radical polymerization (ATRP) macroinitiators at the silica nanoparticle surfaces was achieved through surface modification with excess toluene-2,4-diisocynate (TDI), after which the residual isocyanate groups were converted into ATRP macroinitiators. Structurally well-defined polystyrene chains were grown from the nanoparticle surfaces to yield individual particles composed of a silica core and a well-defined, densely grafted outer polystyrene by ATRP, which was initiated by the as-synthesized silica-based macroinitiator. FTIR, NMR and gel permeation chro-matography (GPC) were used to characterize the polystyrene/silica hybrid particles.     

Facile one‐pot method of initiator fixation for surface‐initiated atom transfer radical polymerization on carbon hard spheres

An efficient and novel one‐pot process is developed to immobilize the atom transfer radical polymerization (ATRP) initiators onto the surface of fully pyrolyzed carbon hard spheres (CHSs) via a radical trapping process from the in situ thermal decomposition of bis(bromomethylbenzoyl)peroxide. The CHSs do not require any additional preparative treatment prior to the initiator immobilization. Styrene and methyl methacrylate are polymerized onto initiator‐immobilized CHSs by surface‐initiated atomic transfer radical polymerization (SI‐ATRP). Samples are characterized using Fourier transform infrared, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. These methods of characterization confirmed that all the CHSs are coated with a uniform layer of grafted polymer. This efficient, one‐pot immobilization of ATRP‐initiators represents an exceptionally simple route for the rapid preparation of various polymer‐coated carbon‐based nanomaterials using SI‐ATRP. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3314–3322