Atom Transfer Radical Copolymerization Research Articles

Gradient helical copolymers: synthesis, chiroptical properties, thermotropic liquid crystallinity, and self-assembly in selective organic solvents

A series of novel gradient copolymers R-(−)-poly(StN-grad-C8) were synthesized through atom transfer radical copolymerization of an achiral styrenic monomer, N,N-dimethyl-4-ethenylbenzamide (M-StN), and a chiral bulky vinylterphenyl monomer, (−)-2,5-bis{4′-[(R)-sec-octyloxycarbonyl]phenyl}styrene (R-(−)-M-C8).

Core Cross-Linked Multiarm Star Polymers with Aggregation-Induced Emission and Temperature Responsive Fluorescence Characteristics

Aggregation-induced emission (AIE) active core cross-linked multiarm star polymers, carrying polystyrene (PS), polyethylene (PE), or polyethylene-b-polycaprolactone (PE-b-PCL) arms, have been synthesized through an “arm-first” strategy, by atom transfer radical copolymerization (ATRP) of a double styrene-functionalized tetraphenylethene (TPE-2St) used as a cross-linker with linear arm precursors possessing terminal ATRP initiating moieties. Polyethylene macroinitiator (PE–Br) was prepared via the polyhomologation of dimethylsulfoxonium methylide with triethylborane followed by oxidation/hydrolysis and esterification of the produced PE–OH with 2-bromoisobutyryl bromide; polyethylene-block-poly(e-caprolactone) diblock macroinitiator was derived by combining polyhomologation with ring-opening polymerization (ROP). All synthesized star polymers showed AIE-behavior either in solution or in bulk. At high concentration in good solvents (e.g., THF, or toluene) they exhibited low photoluminescence (PL) intensity d...

Fluorescent quantum yield of pyrene probe in ultrathin polymer films

The fluorescently labelled polymers including pyrene-labelled polystyrene (PyPS) and pyrene-labelled poly(methyl methacrylate) (PyPMMA) with narrow molecular weight distributions were synthesized by the atom transfer radical copolymerization (ATRCP) of styrene or methyl methacrylate with 1-pyrenemethyl methacrylate (PyMMA). The ultrathin PyPS and PyPMMA films with the thickness ranging from 30 nm to 400 nm supported on the quartz slides were prepared by spin-coating. The fluorescent quantum yield (QY) of the pyrene probe in the ultrathin polymer films was investigated by the photoluminescence spectrometer using an integrating sphere detector. The QY decreased with the reduction of film thickness in the sub-200 nm range.

Preparation of hyperstar polymers with encapsulated Au25(SR)18 clusters as recyclable catalysts for nitrophenol reduction.

A robust approach is developed to prepare hyperstar polymer-Au25(SR)18 nanocomposites for catalysis. The synthesis started with atom transfer radical copolymerization of an inimer with a cyclic disulfide-containing methacrylate monomer in a microemulsion to produce hyperbranched copolymers with high molar mass, low polydispersity, and a vital fraction of dangling disulfide groups. The core-shell structured hyperstar polymers were then prepared using hyperbranched copolymers as macroinitiators to polymerize oligo(ethylene glycol) methyl ether methacrylate (Mn = 500) and grow the radiating arms. The hyperstar polymers with disulfide groups were proved to efficiently encapsulate Au25(SR)18 nanoclusters through ligand exchange without destroying the fine structure of the Au25(SR)18 clusters. The obtained hyperstar-Au25(SR)18 nanocomposites showed great stability with no size change after a three-month shelf storage. They were used as efficient catalysts for the catalytic reduction of 4-nitrophenol by NaBH4, showing convenient recovery and reuse without losing catalytic efficiency.

Miktoarm star copolymers from D-(−)-salicin core aggregated into dandelion-like structures as anticancer drug delivery systems: synthesis, self-assembly and drug release

The β-glucoside-based heterofunctional initiator was used in the synthesis of well-defined eight-armed miktopolymers by sequential ring opening polymerization (ROP) of ε-caprolactone (CL) and atom transfer radical (co)polymerization (ATRP) of methyl methacrylate (MMA) and/or tert-butyl methacrylate (tBMA). Consequently, methacrylic acid (MAA) repeating units were introduced via selective cleavage of pendant tert-butyl protecting groups. Both the amphiphilic copolymers and miktoarm copolymers were self-assembled at 37°C and pH 7.4. The aggregates of miktoarm polymers were larger than that formed by polymethacrylate homoarm stars (≥250nm vs ≤200nm). The critical aggregation concentrations (CAC) of (mikto)stars were relatively low (0.006–0.411mg/mL) and decreased with the increase in MAA fraction content. Both MAA-based mikto- and homoarmed (co)polymers with shorter arms exhibited lower doxorubicin (DOX) loading capacity, whereas camptothecin (CPT) was encapsulated preferably by miktostars. The kinetic profiles of drug release showed that the rate of release was higher at acidic environment (pH 5.0) than in neutral pH. In the most cases the studied miktopolymer systems demonstrated the well-controlled delivery of the model anticancer drugs, which can be adjusted by structural parameters of polymeric carriers.

Multiscale Modeling of Mixing Behavior in a 3D Atom Transfer Radical Copolymerization Stirred-Tank Reactor

Multiscale Modeling of Mixing Behavior in a 3D Atom Transfer Radical Copolymerization Stirred-Tank Reactor

SR&NI atom transfer radical random copolymerization of styrene and butyl acrylate in the presence of MPS-functionalized silica aerogel nanoparticles

Hydrophilic silica aerogel nanoparticles’ surface was functionalized with 3-(trimethoxysilyl)propyl methacrylate (MPS). Then, the resultant functionalized nanoparticles were used in grafting through copolymerization of styrene and butyl acrylate by simultaneous reverse and normal initiation technique for atom transfer radical copolymerization (SR&NI ATRP) to synthesize tailor-made random poly (styrene-co-butyl acrylate) nanocomposites with twofold chains. Successful surface modification of hydrophilic silica aerogel nanoparticles with MPS is demonstrated by Fourier transform infrared spectroscopy and thermogravimetric analysis (TG). Nitrogen adsorption/desorption isotherm is applied to examine surface area and structural characteristics of the synthesized silica aerogel nanoparticles. Evaluation of size distribution and morphological studies were also performed by scanning and transmission electron microscopy. Conversion and molecular weight determinations were carried out using gas and size exclusion chromatography, respectively. Addition of MPS-functionalized nanoparticles by 3 mass% results in a decrease in conversion from 71 to 46 %. Molecular weight (M n) of the free poly (styrene-co-butyl acrylate) chains decreases by adding 3 mass% MPS-functionalized silica aerogel nanoparticles; however, polydispersity index (PDI) value increases from 1.17 to 1.48. Although PDI values of the attached poly (styrene-co-butyl acrylate) chains are increased from 1.54 to 1.76, M n values reveal an increment by adding silica aerogel nanoparticles. 1H NMR spectroscopy results indicate that the molar ration of each monomer in the copolymer chains is approximately similar to the initial selected mole ratio of the monomers. Increasing thermal stability of the nanocomposites is demonstrated by TG. Differential scanning calorimetry also shows a decrease in glass transition temperature by increasing modified silica aerogel nanoparticles.

Atom transfer radical polymerization and copolymerization of isoprene catalyzed by copper bromide/2,2′-bipyridine

Abstract ATRP, as one of the most successful controlled/“living” radical polymerization techniques, has been applied to a large variety of monomers including styrenes, (meth)acrylates, (meth)acrylamides, acrylonitrile, and vinyl acetate. However, ATRP of isoprene still remains a challenge due to poor solubility of copper catalysts in isoprene and low chain propagation rate constant of the monomer. In this work, CuBr/2,2′-bipyridine was found to effectively mediate ATRP of isoprene at 100 °C, 130 °C, and 150 °C with ethyl 2-bromopropionate as an initiator. The polymerizations proceeded smoothly and reached 48.1%, 53.3%, and 71.0% conversions, respectively, in 72 h, producing polyisoprenes with molecular weights close to theoretical values and relatively narrow distributions. A block copolymer of polystyrene-b-polyisoprene was prepared using CuBr/2,2″-bipyridine as a catalyst and polystyrene as a macroinitiator. The 1 H NMR and 13 C NMR analysis of polyisoprene indicated that the polymer had 88.8% 1,4-addition structure and 63.9% of the polymer backbone units were in trans-configuration.

Tribological properties of cross-linked oleophilic polymer brushes on diamond-like carbon films

Surface-initiated atom transfer radical copolymerization of hexyl methacrylate (HMA) and 3-ethyl-3-oxetanylmethyl methacrylate (OxMA) was carried out on the surfaces of block- and ring-type steel pieces covered with silicon-incorporated diamond-like carbon (DLC-Si) in order to generate an oleophilic copolymer brush layer at the outermost surface. The sample was then immersed in a 1% BF3OEt2 solution to form cross-linkages between oxetane groups in the polymer brush chains. The thickness of the polymer brush layer was confirmed to be 50 nm through transmission electron microscope images of the focused ion beam (FIB)-fabricated cross section. The friction properties of the composite films were evaluated using block-on-ring tests under a load of 49 N (130 MPa), using a base oil at 353 K for 30 min. Although the brush layer was partially scratched from the substrate surface during the friction test, the polymer brush-immobilized DLC-Si exhibited a low friction coefficient of 0.02, while the friction coefficient of the non-modified steel substrate was 0.12. It is supposed that the oleophilic polymer brush was swollen in the oil to form a stable lubrication layer, thus preventing the direct contact of the DLC-Si substrate. The dependency of the tribological properties on normal load, sliding velocity, wear depth, and the silicon content of the DLC-Si substrate was also investigated.

Synergetic effect of the epoxide functional groups in the photocatalyzed atom transfer radical copolymerization of glycidyl methacrylate

Methyl methacrylate (MMA) and glycidyl methacrylate (GMA) were copolymerized by photocatalyzed atom transfer radical polymerization under visible light irradiation. The polymerization was made faster by the epoxide group, which played the role of a reducing agent and thus favored the regeneration of the activator.

Synthesis and characterization of a novel acryl amide-based yttrium imprinted sorbent via the ATRP approach for the preparation of medical-grade 90Y

Abstract Because of its favorable radionuclidic properties (pure beta emitter, E βmax = 2.28 MeV, T 1/2 = 64.1 h), the preparation of carrier free 90Y is of a great importance in radiopharmacy. Herein, we report the synthesis, characterization, and application of a novel yttrium sorbent prepared on the basis of the ion-imprinting concept. The ion-imprinted polymer (IIP) was prepared by atom transfer radical copolymerization of acryl amide (AAm, functional monomer) and N,N′-methylenebisacrylamide (MBAAm) crosslinking agent in the presence of a complex of yttrium ions (template ions) with a homemade chelator, i.e., 2,2-bis(2-bromo-2-methylpropanoate)propane-1,3-disuccinate (also as initiator). For elimination of yttrium ions, which act as the template, the prepared particles were treated with 50% v:v HCl : H2O to produce yttrium-imprinted polymeric sorbent. To control the imprinting effect, corresponding non-imprinted particles (NIP) were prepared in a similar manner except that yttrium ions were not used. The synthesized chemicals for the preparation of the chelator-initiator compound and the product itself were assessed in every step using 1H-NMR analysis. NIP and YIP were subjected to X-ray diffraction (XRD), infra-red spectroscopy (IR) and BET surface area analysis for characterization studies. Sorption/desorption studies were conducted, and the effects of potentially interfering ions, such as Sr2+ (α = 119.69) and Zr4+ (α = 73.01) in presence of radio-yttrium, were investigated (particle size: 50–100 μm, resultant recovery of > 99% within 60 min and a capacity of 33.33 mg Y(III) per gram of sorbent). The results showed that amounts of radio-yttrium as low as 250 μg could be extracted effectively with high radionuclidic and radiochemical purity from macro-gram amounts of strontium.

Pickering emulsions stabilized by self-assembled colloidal particles of amphiphilic branched random poly(styrene- co -acrylic acid)

Amphiphilic branched random poly(styrene-co-acrylic acid) (BPSAA) is facilely synthesized by a one-pot atom transfer radical copolymerization of styrene and tert-butyl acrylate with 1-(chloromethyl)-4-ethenylbenzene as chain transfer monomer followed by hydrolysis of ester groups. Then the self-assembled colloidal particles of BPSAA are prepared by a selective solvent method and used to stabilize Pickering emulsions. The influences of pH, branching degree, and salinity on the structure and emulsifying performance of the colloidal particles are investigated. The results show that the BPSAA colloidal particles exhibit pH responsiveness. They can stabilize O/W emulsions effectively at strongly alkaline conditions rather than acidic or weakly alkaline conditions. It is probably due to the random distribution of hydrophobic and hydrophilic microdomains in the colloidal structure restrains the ionization of carboxyl groups and leads to high pKa. The branched structure of the copolymer plays an important role in the colloidal structure and emulsification. The colloidal particles of the BPSAA copolymer with higher degree of branching exhibit higher ionization of carboxyl groups at same pH condition, thus better hydrophilicity and emulsifying performance. In addition, a high NaCl salinity can reduce the electrostatic repulsion among the colloidal particles significantly by shielding effect, to make the colloidal particles flocculate. The formed flocs show an enhanced emulsifying performance. This study may contribute to understand the relationship between the structure and emulsifying performance of polymeric self-assembled colloidal particles.

Synthesis and Characterization of Silica Aerogel-Dispersed Random Poly(styrene-co-butyl acrylate) Nanocomposites by Atom Transfer Radical Copolymerization: A Reverse Approach

Hexamethyldisilazane (HMDS) was employed to surface modification of hydrophilic silica aerogel nanoparticles. Then, the resultant HMDS-modified silica aerogel nanoparticles were used for in situ reverse atom transfer radical copolymerization. Fourier transform infrared spectroscopy, nitrogen adsorption/desorption isotherm, scanning and transmission electron microscopy were employed to evaluate unique characteristics of the HMDS-modified silica aerogel nanoparticles. According to the kinetics results, adding of HMDS-modified silica aerogel nanoparticles by 3 wt% results in a decrease of conversion from 97 to 74 % and molecular weight of copolymer chains from 11,770 to 8384 g mol−1; however, polydispersity index values increases from 1.32 to 1.74. Copolymers composition was evaluated using 1H NMR spectroscopy. TGA results indicate that by increasing HMDS-modified silica aerogel nanoparticles content, slight improvement in thermal stability of the nanocomposites were obtained. DSC results show a decrease in Tg from 39.96 to 30.61 °C by addition of 3 wt% HMDS-modified silica aerogel nanoparticles.

Modeling of the ATRcoP Processes of Methyl Methacrylate and 2‐(Trimethylsilyl) Ethyl Methacrylate in Continuous Reactors: From CSTR to PFR

From the chemical reactor engineering viewpoint, the material flow pattern in continuous reactor can influence the reaction characteristics and reactor performance. Based on the molar balance equations and the method of moments, a tubular reactor model was developed, which was validated using the experimental data from the open reports. Then the atom transfer radical copolymerization (ATRcoP) of methyl methacrylate (MMA) and 2‐(trimethylsilyl) ethyl methacrylate (HEMA‐TMS) under different axial dispersions in tubular reactor were simulated using the developed model. The main ATRcoP behaviors and polymer micro‐characteristics were obtained. Finally, the effects of flow patterns (including the CSTR and PFR modes) on the ATRcoP characteristics were investigated using the models. The simulation results show that the reaction characteristics of the same ATRcoP system produced in flow with different axial dispersion levels are obviously different. Moreover, the comparison of properties such as monomer conversion, dispersity, copolymer composition, and chain‐end functionality between two extreme flow patterns, i.e plug flow in tubular reactor and completely mixed flow in CSTR, were performed. The compositions along the copolymer chain for the two flow modes are very close. As for the other three properties, the tubular reactor has its own comparative advantages over the CSTR.

Maleimide-Functionalized Thiol Reactive Copolymer Brushes: Fabrication and Post-Polymerization Modification

Polymer brushes that present side chain functional reactive groups are attractive platforms for the development of functional surface coatings. From the wide spectrum of possible postpolymerization modification reactions, thiol-based conjugation chemistries are particularly appealing as they can be performed reagent-less under mild conditions and can allow the site-selective conjugation of biomolecules. This manuscript reports a direct approach for the preparation of maleimide-functionalized polymer brushes. These brushes were obtained by surface-initiated atom transfer radical copolymerization of poly(ethylene glycol) methacrylate and a furan-protected, maleimide containing monomer, followed by a thermally induced retro Diels–Alder reaction to unmask the maleimide groups. The feasibility of these brushes to serve as a platform for postpolymerization functionalization was explored in a series of model experiments using a variety of low molecular weight thiols, including a fluorescent dye and a thiol-modified biotin-derivative. The biotinylated brushes were subsequently used for the immobilization of streptavidin-coated quantum-dots. The copolymer brushes presented in this manuscript are attractive since they combine the nonbiofouling properties of the poly(ethylene glycol) methacrylate monomer with the chemoselective reactivity of the maleimide containing monomer, which makes them an attractive platform, e.g., for the immobilization of biomolecules.

Oxygen-nitrogen switchable copolymers of 2,2,2-trifluoroethyl methacrylate and n,n-dimethylaminoethyl methacrylate.

In this work, a novel class of O2 /N2 switchable polymers is reported, which is prepared by atom transfer radical copolymerization (ATRcoP) of commercially available 2,2,2-trifluoroethyl methacrylate (FMA) and N,N-dimethylaminoethyl methacrylate (DMA). The copolymer is random and contains 10 FMA units and 85 DMA units. Its aqueous solution becomes transparent with O2 bubbling and turns to turbid with N2 purging. This O2 /N2 -responsive switchability between the transparent and turbid states is reversible. The FMA-DMA copolymer is thermosensitive and has a lower critical solution temperature (LCST) of 24.5 °C. O2 molecules interact with fluorinated groups of the copolymer and increase the LCST to 55 °C. Purging N2 removes O2 and returns the polymer thermosensitivity back to its initial state. The switchability occurs in the whole temperature range (24.5-55 °C).

Preparation of polymer latex particles carrying salt-responsive fluorescent graft chains

We prepared the novel fluorescent polymer latex particles which can change their fluorescence intensity in response to the increasing NaCl concentration in water. Core polymer latex particles were synthesized by emulsifier-free emulsion polymerization of styrene and 2-(2-chloroisobutyroyloxy)ethyl methacrylate. Hydrophilic polymer chains containing epoxy groups were grafted from the core particles by surface-initiated atom transfer radical copolymerization of methoxy polyethyleneglycol methacrylate (MEOxMA, x = 4 or 9) and glycidyl methacrylate in aqueous media. After azidation of epoxy groups in graft chains, a water-soluble fluorescent dansyl derivative was successfully coupled with the graft chains by copper-catalyzed azide-alkyne cycloaddition in aqueous media. The wavelength of maximum fluorescence intensity of polymer particles carrying graft chains with longer PEG side chains (x = 9) was slightly blue-shifted (7 nm) and the fluorescence intensity increased (1.35 times) with an increase in NaCl concentration as opposed to polymer particles with shorter PEG chains (x = 4).

Sulfolane: an Efficient and Universal Solvent for Copper-Mediated Atom Transfer Radical (co)Polymerization of Acrylates, Methacrylates, Styrene, and Vinyl Chloride.

A very fast and controlled atom transfer radical (co)polymerization (ATRP) of acrylates, methacrylates, styrene, and vinyl chloride is reported in a single dipolar aprotic solvent, sulfolane, with the use of ppm amount of the copper catalyst. The observed rates of polymerization (kpapp) of the monomers studied are similar to those reported using dimethyl sulfoxide (DMSO) and other polar solvents typically employed in single electron transfer (SET)-mediated atom transfer radical polymerization (ATRP) processes. As proof-of-concept, ABA type block copolymers of polystyrene-b-poly(vinyl chloride)-b-polystyrene and poly(methyl acrylate)-b-poly(vinyl chloride)-b-poly(methyl acrylate) were prepared for the first time using a reversible deactivation radical polymerization (RDRP) method in a single solvent. The quantitative preservation of halide chain-ends was confirmed by 1H NMR and MALDI-TOF analysis as well as by the complete shift of the GPC traces. The results presented establish an innovative and robust system to afford a vast portfolio of (co)polymers in a single widely used industrial solvent.

Modeling of the Atom Transfer Radical Copolymerization Processes of Methyl Methacrylate and 2-(Trimethylsilyl) Ethyl Methacrylate under Batch, Semibatch, and Continuous Feeding: A Chemical Reactor Engineering Viewpoint

A kinetic model was developed for the atom transfer radical copolymerization (ATRcoP) of methyl methacrylate (MMA) and 2-(trimethylsilyl) ethyl methacrylate (HEMA-TMS) in tank reactors under three typical feeding modes, namely, batch, semibatch, and continuous feeding. The kinetic parameters for ATRcoP equilibrium were estimated from the model using the experiment data obtained under the batch mode. The simulation results were validated using the experimental data for the semibatch process. An excellent agreement between experiment and simulation data suggests that the model is suitable for simulating the copolymerization. The effects of different operating modes on the ATRcoP characteristics were investigated. The results demonstrated that each reactor possesses its own advantages and disadvantages. Furthermore, this study offers thorough polymerization characteristics comparison with the use of a constant ATRcoP system, and the results show a promising design in determining the optimal operating conditi...

Kinetic modeling of atom transfer radical copolymerization of methyl methacrylate and 2‐(trimethylsilyl) ethyl methacrylate in a train of continuous stirred‐tank reactors

A comprehensive model was developed using the method of moments to describe the atom transfer radical copolymerization (ATRcoP) of methyl methacrylate and 2‐(trimethylsilyl) ethyl methacrylate in a train of continuous stirred‐tank reactors (CSTRs). The use of a train of CSTRs effectively decreases the residence time distribution and molecular weight distribution. Two different constraint conditions (i.e., constant feeding flow rate and constant total average residence time) were simulated. At constant feeding flow rate, the monomer conversion and average molecular weight are significantly improved by increasing the number of CSTRs in the train. Moreover, a constant total average residence time increases the productivity of copolymers with the increase in the number of CSTRs in the series. Thus, a train of CSTRs can be used to produce copolymers continuously with consistent quality. This method is important in obtaining a balance between the quality and quantity of the copolymer production for ATRcoP. POLYM. ENG. SCI., 55:1030–1038, 2015. © 2014 Society of Plastics Engineers