Thermosensitive hairy hybrid nanoparticles synthesized by surface-initiated atom transfer radical polymerization

This article reports on the synthesis of thermosensitive polymer brushes on silica nanoparticles by atom transfer radical polymerization (ATRP) and the study of thermo-induced phase transitions in water. Silica nanoparticles were prepared by the St?ber process and the surface was functionalized by an ATRP initiator. Surface-initiated ATRPs of methoxydi(ethylene glycol) methacrylate (DEGMMA) and methoxytri(ethylene glycol) methacrylate (TEGMMA) were carried out in THF at 40 degrees C in the presence of a free initiator, benzyl 2-bromoisobutyrate. The polymerizations were monitored by 1H NMR spectroscopy and gel permeation chromatography. The hairy hybrid nanoparticles were characterized by thermogravimetric analysis and scanning electron microscopy, and the thermoresponsive properties were investigated by variable temperature 1H NMR spectroscopy and dynamic light scattering. The cloud points of free poly(DEGMMA) and poly(TEGMMA) in water were around 25 and 48 degrees C, respectively. The thermo-induced phase transitions of polymer brushes on silica nanoparticles began at a lower temperature and continued over a broader range (4-10 degrees C) than those of free polymers in water (< 2 degrees C).     

Tertiary amine-functionalized polymers by atom transfer radical polymerization

The quantitative synthesis of tertiary amine-functionalized polymers by atom transfer radical polymerization is reported. Tertiary amine-functionalized polystyrene was prepared with the adduct of 1-(bromoethyl)benzene with 1-(4-dimethyl-aminophenyl)-1-phenylethylene as an initiator in the atom transfer radical polymerization of styrene in the presence of a copper (I) bromide/2,2′-bipyridyl catalyst system. The polymerization proceeded via a controlled free-radical polymerization process to afford quantitative yields of the corresponding tertiary amine-functionalized polystyrene with predictable number-average molecular weights (1600–4400), narrow molecular weight distributions (1.09–1.31), and an initiator efficiency of 0.95. The polymerization process was monitored by gas chromatographic analysis. The tertiary amine-functionalized polymers were characterized by thin-layer chromatography, size exclusion chromatography, potentiometry, and spectroscopy. All experimental evidence was consistent with quantitative functionalization via the 1,1-diphenylethylene derivative. Polymerization kinetic measurements showed that the polymerization reaction followed first-order-rate kinetics with respect to monomer consumption and that the number-average molecular weight increased linearly with monomer conversion. © 2001 John Wiley & Sons, Inc. J Polym Sci A Part A: Polym Chem 39: 2058–2067, 2001     

Protein-resistant polymer coatings on silicon oxide by surface-initiated atom transfer radical polymerization

The modification of silicon oxide with poly(ethylene glycol) to effectively eliminate protein adsorption has proven to be technically challenging. In this paper, we demonstrate that surface-initiated atom transfer radical polymerization (SI-ATRP) of oligo(ethylene glycol) methyl methacrylate (OEGMA) successfully produces polymer coatings on silicon oxide that have excellent protein resistance in a biological milieu. The level of serum adsorption on these coatings is below the detection limit of ellipsometry. We also demonstrate a new soft lithography method via which SI-ATRP is integrated with microcontact printing to create micropatterns of poly(OEGMA) on glass that can spatially direct the adsorption of proteins on the bare regions of the substrate. This ensemble of methods will be useful in screening biological interactions where nonspecific binding must be suppressed to discern low probability binding events from a complex mixture and to pattern anchorage-dependent cells on glass and silicon oxide.     

Dehalogenation of polymers prepared by atom transfer radical polymerization

Polymers prepared by atom transfer radical polymerization (ATRP) have well‐defined end groups, predetermined by the initiator used. A typical initiator is an alkyl halide from which the halogen is transferred to one chain end. To remove the halogen end group, dehalogenation with trialkyltin hydride has been used. Procedures for the removal of the polymer halogen end groups are described, one of them being a one‐pot reaction where the dehalogenation of the polymer chain ends occurs immediately after polymerization.     

Facile synthesis of thermally stable poly(N-vinylpyrrolidone)-modified gold surfaces by surface-initiated atom transfer radical polymerization

Well-controlled polymerization of N-vinylpyrrolidone (NVP) on Au surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP) was carried out at room temperature by a silanization method. Initial attempts to graft poly(N-vinylpyrrolidone) (PVP) layers from initiators attached to alkanethiol monolayers yielded PVP films with thicknesses less than 5 nm. The combined factors of the difficulty in the controllable polymerization of NVP and the instability of alkanethiol monolayers led to the difficulty in the controlled polymerization of NVP on Au surfaces. Therefore, the silanization method was employed to form an adhesion layer for initiator attachment. This method allowed well-defined ATRP polymerization to occur on Au surfaces. Water contact angle, X-ray photoelectron spectroscopy (XPS), and reflectance Fourier transform infrared (reflectance FTIR) spectroscopy were used to characterize the modified surfaces. The PVP-modified gold surface remained stable at 130 °C for 3 h, showing excellent thermal stability. Thus, postfunctionalization of polymer brushes at elevated temperatures is made possible. The silanization method was also applied to modify SPR chips and showed potential applications in biosensors and biochips.     

Synthesis and characterization of surface-initiated polymer brush prepared by reverse atom transfer radical polymerization

Surface-initiated reverse atom transfer radical polymerization (reverse ATRP) technique was used to synthesize well-controlled nanostructure of polymer brushes from silicon wafer. Kinetic studies revealed a linear increase in polymer film thickness with reaction time, indicating that chain growth from surface was a controlled process with a “living” characteristic. This technique provides a simple and efficient approach to create various nanostructures of polymer brushes potentially used for designing nanodevices. Analysis of the polymer brush layers was conducted using ellipsometry, XPS, AFM and contact angle measurements, respectively.     

New (Co)polymers by atom transfer radical polymerization

The fundamentals of atom transfer radical polymerization (ATRP) are presented. This includes the mechanistic considerations including structure of active and dormant species and structural features of the catalyst and reaction conditions as well as the nature of initiation and propagation steps. Extension of homogeneous polymerization to heterogeneous systems including emulsion polymerization is presented. Synthesis of (co)polymers with predefined molecular weights and low polydispersites as well as with controlled compositions, functionalities and architectures is reviewed.     

Fuzzy ternary particle systems by surface-initiated atom transfer radical polymerization from layer-by-layer colloidal core-shell macroinitiator particles

We report the synthesis of ternary polymer particle material systems composed of (a) a spherical colloidal particle core, coated with (b) a polyelectrolyte intermediate shell, and followed by (c) a grafted polymer brush prepared by surface-initiated polymerization as the outer shell. The layer-by-layer (LbL) deposition process was utilized to create a functional intermediate shell of poly(diallyl-dimethylammonium chloride)/poly(acrylic acid) multilayers on the colloid template with the final layer containing an atom transfer radical polymerization (ATRP) macroinitiator polyelectrolyte. The intermediate core-shell architecture was analyzed with FT-IR, electrophoretic mobililty (zeta-potential) measurements, atomic force microscopy, and transmission electron microscopy (TEM) techniques. The particles were then utilized as macroinitiators for the surface-initiated ATRP grafting process for poly(methyl methacrylate) polymer brush. The polymer grafting was confirmed with thermo gravimetric analysis, FT-IR, and TEM. The polymer brush formed the outermost shell for a ternary colloidal particle system. By combining the LbL and surface-initiated ATRP methods to produce controllable multidomain core-shell architectures, interesting functional properties should be obtainable based on independent polyelectrolyte and polymer brush behavior.     

A novel hydrophilic polystyrene-based beads for hydrophilic interaction chromatography by surface-initiated atom transfer radical polymerization

A one-step procedure to hydrophilize monodisperse poly(chloromethyl-styrene-co-divinylbenzene) beads has been presented with 2-hydroxy-3-[4-(hydroxymethyl)-1H-1,2,3-triazol-1-yl]propy1 2-methylacrylate(HTMA) as monomer by surface-initiated atom transfer radical polymerization(SI-ATRP).The length of the grafted poly(HTMA) chain was varied via controlling the ratio of HTMA to initiator on the surface of the beads.Using these grafted beads as the stationary phase in hydrophilic interaction chromatography,good separation was obtained for nucleosides in the mobile phase of acetonitrile-water.It was also found that the retention time and selectivity of solutes showed a positive relationship with the length of the grafted poly(HTMA) chain.     

Surface modification of PDMS by surface-initiated atom transfer radical polymerization of water-soluble dendronized PEG methacrylate

The current paper reports the synthesis of a highly hydrophilic, antifouling dendronized poly(3,4,5-tris(2-(2-(2-hydroxylethoxy)ethoxy)ethoxy)benzyl methacrylate) (PolyPEG) brush using surface initiated atom transfer radical polymerization (SI-ATRP) on PDMS substrates. The PDMS substrates were first oxidized in H₂SO₄/H₂O₂ solution to transform the Si-CH₃ groups on their surfaces into Si-OH groups. Subsequently, a surface initiator for ATRP was immobilized onto the PDMS surface, and PolyPEG was finally grafted onto the PDMS surface via copper-mediated ATRP. Various characterization techniques, including contact angle measurements, attenuated total reflection infrared spectroscopy, and X-ray photoelectron spectroscopy, were used to ascertain the successful grafting of the PolyPEG brush onto the PDMS surface. Furthermore, the wettability and stability of the PDMS-PolyPEG surface were examined by contact angle measurements. Anti-adhesion properties were investigated via protein adsorption, as well as bacterial and cell adhesion studies. The results suggest that the PDMS-PolyPEG surface exhibited durable wettability and stability, as well as significantly anti-adhesion properties, compared with native PDMS surfaces. Additionally, our results present possible uses for the PDMS-PolyPEG surface as adhesion barriers and anti-fouling or functional surfaces in biomedical applications.     

Tethering hydrophilic polymer brushes onto PPESK membranes via surface-initiated atom transfer radical polymerization

Surface-initiated atom transfer radical polymerization (ATRP) was used to graft hydrophilic comb-like poly((poly(ethylene glycol) methyl ether methacrylate), or P(PEGMA), brushes from chloromethylated poly(phthalazinone ether sulfone ketone) (CMPPESK) membrane surfaces. Prior to ATRP, chloromethylation of PPESK was beforehand performed and the obtained CMPPESK was prepared into porous membranes by phase inversion process. It was demonstrated that the benzyl chloride groups on the CMPPESK membrane surface afforded effective macroinitiators to graft the well-defined polymer brushes. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the grafting of P(PEGMA) chains. Water contact angle measurements indicated that the introduction of P(PEGMA) graft chains promoted remarkably the surface hydrophilicity of PPESK membranes. The effects of P(PEGMA) immobilization on membrane morphology, permeability and fouling resistance were investigated. It was found that the comb-like P(PEGMA) grafts brought smaller pore diameters and higher solute rejections to PPESK membranes. The results of dynamic anti-fouling experiments showed the anti-fouling ability of the membranes was significantly improved after the grafting of P(PEGMA) brushes.     

Immobilized copper catalyst for atom transfer radical addition and polymerization

A novel multidentate amine grafted on silica gel and magnetic microsphere was prepared. Its chemical structure was confirmed by C¹³ NMR, XPS and FTIR, and the nitrogen content was determined by elemental analysis. It was also used as a ligand for CuCl and successfully catalyzed the atom transfer radical addition of both carbon tetrachloride (CCl₄) to methyl methacrylate and methyl trichloroacetate to styrene, repeatedly. The conversion and purity of the product were determined through gas chromatography and ¹H NMR, respectively. The immobilized copper catalyst complex was also used in atom transfer radical polymerization of styrene initiated by 1,1,1,3‐tetrachloro‐3‐phenylpropane and methyl methacrylate initiated by methyl 2‐methyl‐2,4,4,4‐tetrachlorobutyrate, respectively. Although the polymerization took place successfully, it did not proceed in a controlled fashion. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of polymers with hydroxyl end groups by atom transfer radical polymerization

Polymers prepared by atom transfer radical polymerization (ATRP) contain end groups defined by the initiator used. Alkyl halides, used as initiators, lead to polymers with an alkyl group at one end and a halide as the other chain end. Using functionalized initiators such as 2‐hydroxyethyl 2‐bromopropionate, hydroxyl groups can be directly incorporated at one polymer chain end while the other end functionality remains a halogen. The direct displacement of the halogen end groups with hydroxyl groups was unsuccessful due to side reactions such as elimination (for polystyrene) or hydrolysis of ester functions (for polyacrylate). Another approach to generate hydroxyl end groups was based on the substitution of the halogen end groups by ethanolamine. This was successful for polystyrene but additional substitution at the backbone esters was observed in polyacrylates. Multiple substitution reactions could be avoided by using 4‐aminobutanol instead of 2‐aminoethanol. Hydroxyl terminated polyacrylates were also obtained by extending the polyacrylate chain end with one allyl alcohol unit in a one‐pot process by adding an excess of allyl alcohol at the end of e polymerization of acrylate.     

Cysteine-reactive polymers synthesized by atom transfer radical polymerization for conjugation to proteins

In this communication we report a strategy for the synthesis of semitelechelic polymers reactive to cysteines. An initiator modified with a pyridyl disulfide was prepared and used for the CuBr/2,2'-bipyridine-mediated atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate. Polydispersity indices (M(w)/M(n)) of the polymers with different molecular weights were 1.25 or less. The pyridyl disulfide end group was preserved during the polymerization and allowed direct conjugation of the polymer to cysteine residues of bovine serum albumin. The described method provides a general way for the preparation of protein-polymer conjugates through a reversible disulfide bond without the need for postsynthesis modification of the polymers.     

Preparation of imidazole-functionalized silica by surface-initiated atom transfer radical polymerization and its application for hydrophilic interaction chromatography

A novel imidazole-functionalized stationary phase for hydrophilic interaction chromatography (HILIC) was prepared via surface-initiated atom transfer radical polymerization (SI-ATRP). 1-Vinylimidazole as a monomer was polymerized on the surface of initiator-immobilized silica by SI-ATRP using CuCl and 2,2'-bipyridyl as a catalyst. The graft chain length and polymer grafting density were controlled by varying the ratio of monomer to initiator. The resulting materials were characterized by elemental analysis and thermogravimetric analysis. Then, high-performance liquid chromatography separation of eight nucleobases/nucleosides was performed on the imidazole-functionalized chromatographic column in HILIC mode. The effects of mobile phase composition, buffer pH, and column temperature on the separation of nucleobases/nucleosides were investigated, and the retention mechanisms were studied. Chromatographic parameters were calculated, and the results showed that surface adsorption through hydrogen bonding and electrostatic interaction dominated the retention behavior of the solutes in HILIC mode. Lastly, the stationary phase was successfully used to determine the nucleobases and nucleosides from Cordyceps militaris.     

On surface-initiated atom transfer radical polymerization using diazonium chemistry to introduce the initiator layer

This work features the controllability of surface-initiated atom transfer radical polymerization (SI-ATRP) of methyl methacrylate, initiated by a multilayered 2-bromoisobutyryl moiety formed via diazonium chemistry. The thickness as a function of polymerization time has been studied by varying different parameters such as the bromine content of the initiator layer, polarity of reaction medium, ligand type (L), and the ratio of activator (Cu(I)) to deactivator (Cu(II)) in order to ascertain the controllability of the SI-ATRP process. The variation of thickness versus surface concentration of bromine shows a gradual transition from mushroom to brush-type conformation of the surface anchored chains in both polar and nonpolar reaction medium. Interestingly, it is revealed that very thick polymer brushes, on the order of 1 μm, can be obtained at high bromine content of the initiator layer in toluene. The initial polymerization rate and the overall final thickness are higher in the case of nonpolar solvent (toluene) compared to polar medium (acetonitrile or N,N-dimethylformamide). The ligand affects the initial rate of polymerization, which correlates with the redox potentials of the pertinent Cu(II)/Cu(I) complexes (L = Me(6)TREN, PMDETA, and BIPY). It is also observed that the ability of polymer brushes to reinitiate depends on the initial thickness and the solvent used for generating it.     

Synthesis of novel crosslinkable polymers by atom transfer radical polymerization of cardanyl acrylate

In this work, the successful application of atom transfer radical polymerization (ATRP) to cardanyl acrylate, a polymerizable monomer derived from a renewable resource cardanol, is reported. Polycardanyl acrylate and poly(methylmethacrylate)‐cardanyl acrylate copolymers were prepared in bulk ATRP, using Copper(I) bromide/N, N, N′, N′, N″‐pentamethyl diethylene triamine (PMDETA) catalyst system at 95 °C in combination with ethyl‐2‐bromo isobutyrate initiator. The copolymers had mol. wt. (M_n) in the range 8300–2400 g/mol and polydispersity index (PDI) 1.27–2.00, depending upon the [M]₀/[I]₀ ratio. ¹H NMR analysis of the copolymer showed that unsaturation in the side chain of cardanyl acrylate is unaffected under the conditions of ATRP. This was further confirmed by studying the curing reaction of polycardanyl acrylate by supported dynamic mechanical thermal analysis (DMTA) in dual cantilever mode. The thermogravimetric analysis shows that the copolymers have improved thermal stability, by about 35 °C, in comparison with pure PMMA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5953–5961, 2005     

Grafting of polymethyl methacrylate from poly(ethylene-co-vinylacetate) copolymer using atom transfer radical polymerization

Atom transfer radical polymerization was employed for the first time to prepare graft copolymer having by ethylene-vinyl acetate (EVA) copolymer as backbone and poly(methyl methacrylate) (PMMA) as branches. The polymerization of MMA was initiated by EVA carrying chloropropionate groups as macroinitiator, in the presence of copper chloride (CuCl) and bipyridine (bpy) at 80 °C. The macroinitiator was prepared by esterification of partially hydrolyzed EVA with 2-chloropropionyl chloride. Successful graft copolymerizations were performed both in toluene/γ-butyrolactone mixed solvent and in toluene solution, with grafting efficiency of 12% and 6%, respectively. Molecular weight distribution of the PMMA segments around 1.2 has been achieved with pure toluene solution. The ATRP graft copolymerization was supported by an increase of the molecular weight of the graft copolymers, as compared to that of the macroinitiator and also by their monomodal molecular weight distribution.