Atom Transfer Radical Polymerization Procedures Research Articles

Polymeric microcarrier for diagnostic assays and gene delivery systems

The interaction of deoxyribonucleic acid (DNA) with polymeric nano- and microcarriers has attracted significant attention in the studies on DNA diagnostic assays, DNA isolation and particularly gene delivery and cancer therapy agents. Therefore, in this study, plain poly(glycerol dimethacrylate) (poly(GDMA)) and poly(dimethylaminoethyl methacrylate)-grafted poly(GDMA) microgel particles were synthesized for high single-stranded DNA (ssDNA) adsorption and desorption capacity. Temperature- and pH-sensitive uniform poly(GDMA) particles were synthesized through a two-stage procedure. A GDMA dispersion polymerization procedure was used in the first stage of the study to obtain microgel particles with approximately 900 nm size. The surface-initiated atom transfer radical polymerization procedure, a living-polymerization technique of 2-dimethylaminoethyl methacrylate (DMAEM), was used in the second stage of the study to obtain polycationic molecular brushes on microgel particles. The resulting temperature- and pH-responsive microgels were used as a sorbent for ssDNA adsorption. Compared with commonly used sorbents, reasonably high ssDNA adsorptions were achieved with the proposed sorbent. The adsorbed ssDNA was desorbed from the sorbent at a high yield. The adsorption and desorption behaviors make poly(DMAEM)-grafted poly(GDMA) microgel particles a promising carrier/sorbent for ssDNA.

Synthesis of Riboflavin‐Based Macromolecules through Low ppm ATRP in Aqueous Media

AbstractA vitamin‐B2‐based macroinitiator is prepared by esterification of riboflavin with 2‐bromoisobutyryl bromide. Following the “core first” methodology, “phoenix”‐shape (co)polymers with a polar riboflavin core and either a hydrophobic (poly(n‐butyl acrylate) or poly(methyl methacrylate)) or hydrophilic (poly(N‐isopropylacrylamide)‐block‐poly(oligo(ethylene glycol) acrylate) or poly(N‐isopropylacrylamide)‐block‐poly(2‐hydroxyethyl acrylate)) tails are synthesized via low ppm atom transfer radical polymerization procedures. Polymers have predetermined molecular weights and a low dispersity (Ð < 1.2). 1H NMR analysis confirms the successful formation of targeted (co)polymers with the preserved riboflavin functionality.

ATRP of N‐Hydroxyethyl Acrylamide in the Presence of Lewis Acids: Control of Tacticity, Molecular Weight, and Architecture

Good control of tacticity, molecular weight, and architecture is attained via atom transfer radical polymerization (ATRP) of N-hydroxyethyl acrylamide (HEAA), in a one-pot process in the presence of Y(OTf)3 . The effect of temperature, ratio of [Y(OTf)3 ]/[HEAA], and ATRP procedure on the tacticity and degree of control over the polymerization is investigated in detail. Under optimal conditions, using photo ATRP and 15% Y(OTf)3, the content of meso dyads (m) can be increased from 42% to 80% in a homopolymer with a dispersity D=1.22. Well-defined stereoblock copolymers, atactic- b -isotactic poly(HEAA), with D=1.27, are obtained by adding Y(OTf)3 at a specific conversion, initially started without Y(OTf)3 .

Advanced Materials by Atom Transfer Radical Polymerization.

Atom transfer radical polymerization (ATRP) has been successfully employed for the preparation of various advanced materials with controlled architecture. New catalysts with strongly enhanced activity permit more environmentally benign ATRP procedures using ppm levels of catalyst. Precise control over polymer composition, topology, and incorporation of site specific functionality enables synthesis of well-defined gradient, block, comb copolymers, polymers with (hyper)branched structures including stars, densely grafted molecular brushes or networks, as well as inorganic-organic hybrid materials and bioconjugates. Examples of specific applications of functional materials include thermoplastic elastomers, nanostructured carbons, surfactants, dispersants, functionalized surfaces, and biorelated materials.

Synthesis and temperature-induced self-assembly of a positively charged symmetrical pentablock terpolymer in aqueous solutions

A novel linear cationic ABCBA pentablock terpolymer composed of a positively charged poly (3-acrylamidopropyl) trimethyl ammonium chloride)) (PAMPTMA (+)) block at both ends and two thermoresponsive poly (N-isopropylacrylamide) (PNIPAAM) blocks separated by a hydrophilic poly(ethylene glycol) (PEG) block was synthesized via a “one-pot” atom transfer radical polymerization procedure (ATRP). The chemical composition of the pentablock terpolymer was confirmed by nuclear magnetic resonance (NMR) and asymmetric flow field-flow fractionation (AFFFF). Depending on the polymer concentration in aqueous solution, this terpolymer forms unimers and self-assembled structures at elevated temperatures. The effect of concentration and temperature-induced self-assembling behavior of the pentablock terpolymer in aqueous solution was examined by using turbidimetry, shear viscosity, rheo-small angle light scattering (rheo-SALS), dynamic light scattering (DLS), and small angle neutron scattering (SANS). The turbidity measurements demonstrated that the formation of intermicellar structures and compaction of the complexes are function of both polymer concentration and temperature. The viscosity and rheo-SALS experiments elucidated the intricate interplay between building-up and breaking-up of interchain complexes under the influence of shear flow. The DLS experiments show the coexistence of small entities and interchain complexes at low temperatures and the evolution of large intermicellar structures at higher temperatures. At the highest temperatures, compaction of the complexes occurred. The results from SANS revealed significant temperature-induced changes of the copolymer structure on a semi-local dimensional scale.

Iron and copper based catalysts containing anionic phenolate ligands for atom transfer radical polymerization

Iron and copper complexes with anionic phenolate-bis(pyridyl)amine ligands were synthesized and examined as catalysts for atom transfer radical polymerization (ATRP) of methyl (meth)acrylate and styrene. With copper complexes, polymers with narrow molecular weight distributions, M w /M n ~1.2, were prepared. The catalytic performance of copper catalysts was affected by nature of halogen species and by the steric and electronic effects. In iron-mediated ATRP procedures, the number-average molecular weights of the polymers increased with monomer conversion, however, the molecular weight distributions of the resulting polymers were relatively broad M w /M n ~1.7, due to slow deactivation processes.

Biodegradable micelles self-assembled from miktoarm star block copolymers for MTX delivery

Biodegradable micelles based on disulfide-linked monomethoxy poly(ethylene glycol)-b-poly(methyl methacrylate)2 (mPEG-SS-PMMA2) miktoarm star block copolymers were synthesized through atom transfer radical polymerization procedure and applied to solubilization and delivery of methotrexate (MTX). The synthesized miktoarm star block copolymers were characterized by 1H nuclear magnetic resonance, Fourier transform infrared spectra, and gel permeation chromatography. The block copolymers were able to self-assemble into spherical micelles in water with an average diameter up to 130 nm by transmission electron microscopy observation and dynamic light scattering measurements and have a critical micelle concentration of 0.91 mg/L. When MTX was incorporated into obtained micelles, high drug loading capacity was found attributed to the designed miktoarm star-shaped nanostructure. Interestingly, in presence of dithiothreitol, the micelles could be degraded into polymer chains by cleavage of the disulfide linkages. The in vitro release studies revealed that these micelles released over 95 % of MTX within 48 h under a reductive environment analogous to that of the cell comparing to minimal drug release (<22 %) under nonreductive conditions. Cell cytoxicity experiments showed that the obtained micelles exhibited nontoxic, and the drug-loaded micelles exhibited high anticancer efficacy and better biocompatibility as compared to free MTX. All of these results showed that mPEG-SS-PMMA2 micelles are promising carriers for delivery of hydrophobic antitumor drugs.

Crystallization of Polymer Brushes with Poly(ethylene oxide) Side Chains

Surface-initiated atom transfer radical polymerization (ATRP) of methoxypoly(ethylene glycol) methacrylate (MPEGMA) macromonomers from immobilized initiators leads to thin films of comblike polymer brushes. The aqueous ATRP procedure results in essentially constant film growth rates and yields coatings with thicknesses as high as 400 nm. Polymers with side chains consisting of 22−23 ethylene oxide repeating units align to form crystalline materials analogous to their nonbrush analogues. However, polarized optical microscopy shows that the polymer films crystallize as two-dimensional spherulites. Both AFM images and reflectance FT-IR spectra of the films are consistent with crystalline lamellae preferentially oriented normal to the surface for brushes with thicknesses above 100 nm. As the film thickness decreases, the favored orientation shifts to crystalline lamellae parallel to the surface, with the PEO side chains oriented perpendicular to the surface. The lamellae orientations are related to polymer−surface interactions as well as to the “comblike” polymeric structure.

Grafting densely-packed poly( n-butyl methacrylate) chains from an iron substrate by aryl diazonium surface-initiated ATRP: XPS monitoring

Poly( n-butyl methacrylate), PBMA, chains were grafted by atom transfer radical polymerization (ATRP) from the surface of iron plates using electrochemically attached initiators based on diazonium salts providing an iron/polyphenylene/PBMA structure. This surface-initiated ATRP procedure was controlled by the addition of a small proportion of Cu ++ deactivator, but in the absence of any sacrificial initiator. Combined XPS, IR and AFM experiments provide a powerful means for the characterization of the obtained complex iron/polyphenylene/PBMA layered structure. It is possible to measure the thickness of the brominated aryl structure covalently attached to iron. Concerning the PBMA brushes, their presence on the surface was confirmed by IRRAS. The brominated chain end could be traced by XPS testifying for the ATRP character of the polymerization and the thickness of the polymer brushes was determined. The controlled living ATRP character of the polymerization is confirmed through a linear correlation between the thickness of the layer and the degree of polymerization. Measurement of the grafting density of PBMA chains indicates that they are compactly packed and that, approximately, one brominated aryl chain out of two efficiently initiates ATRP.

Synthesis and Microphase Separation of Poly(styrene-b-acrylonitrile) Prepared by Sequential Anionic and ATRP Techniques

Carbonaceous templates with nanopores <10 nm in diameter have been produced using low molecular weight diblock copolymers of poly(styrene-b-acrylonitrile). PS-b-PAN was synthesized using sequential living and controlled polymerization approaches, where the first block was anionically synthesized while the second block was added using atom transfer radical polymerization (ATRP). Polystyrene with a hydroxy end group was synthesized anionically and then reacted with 2-bromoisobutyryl bromide to create the ATRP macroinitiator. Acrylonitrile was polymerized using ATRP procedures. Polymer microphase separation, stabilization, and subsequent pyrolysis were characterized by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM).

CdS-Nanoparticle/Polymer Composite Shells Grown on Silica Nanospheres by Atom-Transfer Radical Polymerization

In this paper we describe the combined use of surface-initiated atom transfer radical polymerization (ATRP) and a gas/solid reaction in the direct preparation of CdS-nanoparticle/block-copolymer composite shells on silica nanospheres. The block copolymer, consisting of poly(cadmium dimethacrylate) (PCDMA) and poly(methyl methacrylate) (PMMA), is obtained by repeatedly performing the surface-initiated ATRP procedures in N,N-dimethylformamide (DMF) solution at room temperature, using cadmium dimethacrylate (CDMA) and methyl methacrylate (MMA) as the monomers. CdS nanoparticles with an average size of about 3 nm are generated in situ by exposing the silica nanospheres coated with block-copolymer shells to H2S gas. These synthetic core–shell nanospheres were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), diffuse reflectance UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD). These composite nanospheres exhibit strong red photoluminescence in the solid state at room temperature.

End-group fidelity in nitroxide-mediated living free-radical polymerizations

In this study, new nitroxides based on the 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxy skeleton were used to examine chain-end control during the preparation of polystyrene and poly(t-butyl acrylate) under living free-radical conditions. Alkoxyamine-based initiators with a chromophore attached to either the initiating fragment or the mediating nitroxide fragment were prepared, and the extent of the incorporation of the chromophores at either the initiating end or the propagating chain end was determined. In contrast to 2,2,6,6-tetramethyl piperidinoxy (TEMPO), the incorporation of the initiating and terminating fragment into the polymer chain was extremely high. For both poly(t-butyl acrylate) and polystyrene with molecular weights less than or equal to 70,000, incorporations at the initiating end of greater than 97% were observed. At the terminating chain end, incorporations of greater than 95% were obtained for molecular weights less than or equal to 50,000. The level of incorporation tended to decrease slightly at higher molecular weights because of the loss of the alkoxyamine propagating unit, which had important consequences for block copolymer formation. These results clearly show that these new α-H nitroxides could control the polymerization of vinyl monomers such as styrene and t-butyl acrylate to an extremely high degree, comparable to anionic and atom transfer radical polymerization procedures. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4749–4763, 2000