Atom Transfer Radical Polymerization Process Research Articles

An anionic polyethersulfone membrane modified by poly(2-acrylamide-2-methylpropanesulfonic acid sodium salt) grafted carbon nanotubes

Polyethersulfone membrane is easy to be polluted, and the negative surface would help enhance improve the permeability and the anti-pollution performance; so how to anchor polymer brushes with negative groups to polyethersulfone membrane surface is a challenge. In this paper, polymer brushes of poly(2-acrylamide-2-methylpropanesulfonic acid sodium salt) is first grafted to carbon nanotubes to form an organic-inorganic hybrid additive, which is further anchored onto the membrane surface of polyethersulfone by blending method. The graft reaction is proceeded by surface initiated electrochemical atom transfer radical polymerization, where the introduction of electrochemical part is because it could help better control the growth of polymer brushes compared with the pristine atom transfer radical polymerization process. The carbon nanotubes grafted with poly(2-acrylamide-2-methylpropanesulfonic acid sodium salt) could anchor on the membrane surface because the there is a self-assemble process of organic-inorganic hybrid additive during phase inversion method, where the inorganic part carbon nanotubes firmly embedded into the membrane and the organic part can be fixed on membrane surface. The polyethersulfone membrane exhibits enhanced surface hydrophilicity, improved the permeability of the membrane, and good anti-fouling performance due to the negative charge and electrostatic repulsion brought by anionic surface of the modified membrane. When the mass of nanotubes grafted with poly(2-acrylamide-2-methylpropanesulfonic acid sodium salt) in the casting solution is 20 mg, the water flux can reach 365.5 L m−2 h−1, and the rejection ratios of both BSA and CR are close to 100% with good flux recovery and anti-fouling effect performance.

Random and block architectures of N-arylitaconimide monomers with methyl methacrylate

Abstract “Itaconimide” is the members of imide (–CO–NH–CO–) family with reactive exocyclic double bond and it is easily obtained from the renewable resource i.e. D-glucose. The polymerization of various N-arylitaconimide (NAI) monomers with methyl methacrylate (MMA) have been reported to improve the glass transition temperature (T g) and thermal stability of poly(methyl methacrylate) (PMMA). In literature, these studies have been done mostly using conventional free radical polymerization methods, which restricts the architecture of copolymers to “random” only. The block copolymers of NAI and MMA are an important due to the combination of glassy PMMA and thermally stable poly(NAI), which offers its applications for higher temperature service. The architectural control of polymers in provisions of its topology, composition, and various functionalities is possibly obtained using reversible-deactivation radical polymerizations (RDRPs). In RDRPs, the concentration of free radical is controlled in such a way that the termination reactions are minimized (normally in range of 1–10 mol%), and not allowed to obstruct with the desired architecture. However, this is possible by achieving (or by establishing) a rapid dynamic equilibrium between propagating radical and dormant species (i.e. R–X). Among all RDRPs, the atom transfer radical polymerization (ATRP) is very popular and adaptable method for the synthesis of polymers with specifically controlled architecture. Two different architectures of NAI and MMA copolymers are reported using ATRP process. The effect of various pedant groups on the rate constants of propagation (k p) and thermal properties NAI and MMA copolymers is studied. The poly(NAI-ran-MMA)-b-poly(MMA) are stable up to 200 °C and degraded in three steps. Whereas, the poly(NAI-ran-MMA)-b-poly(NAI) are stable up to 330 °C and degraded in two steps. The density functional theory methods are used for calculation of equilibrium constants (K ATRP) for the ATRP process for the series of laboratory synthesized alkyl halides. A good agreement was observed between the experimentally determined and theoretically calculated K ATRP values. The mechanistic studies are carried for poly(NAI-ran-MMA) copolymer system using statistical model discrimination method along with 1H decoupled 13C NMR spectroscopy. For studying the mechanism of copolymerization of NAI and MMA via ATRP methods, “trimer model or penultimate model” will be more accurate than “dimer model or terminal model”.

The effect of sulfonated copolymer as a binder on the electrochemical performance of LiFePO4 cathode for lithium-ion batteries

In today's market, lithium-ion batteries are proving to be the most promising and effective rechargeable batteries. In the development of active materials with high energy density for batteries, the design of binders is a bottleneck technology, which produces an interconnected electrode structure. In this study, for developing lithium-ion batteries with high efficiency, the sulfonated copolymer was employed as an effective binder. In order to improve the performance of poly(vinylidene fluoride) (PVDF) as a binder for lithium-ion batteries (LIBs), sulfonated PVDF copolymer was prepared in this study using the atom transfer radical polymerization (ATRP) process. The influence of sulfonated PVDF binder on the electrochemical performances of LIBs was assessed using charge and discharge measurements, cycling performance up to 300 cycles, cycling voltammetry (CV), and electrochemical impedance spectroscopy (EIS) analysis. The investigation indicated decreased concentration polarization and improved lithiation and delithiation kinetics at high number of charge/discharge cycles for LiFePO4 electrodes with sulfonated PVDF binders. The discharge capacity after 300 cycles was 90 mAh g−1 with a capacity retention of 100% at 1C. As a result, the copolymer synthesized in this paper can be utilized to design next-generation polymer binders for high-efficiency LIBs.

Self‐Aligned Polymer Film Patterning on Microstructured Silicon Surfaces

AbstractBased on a recently developed selective etching process for silicon samples with buried implants, this work presents a method for utilizing the generated material contrast between silicon and silicon oxide to selectively deposit polymers on the patterned surface. Besides depositing polystyrene selectively on the etched parts via drop‐casting and dewetting, polymer chains are selectively grafted to the oxidic surface parts. To this end, the oxide surfaces are selectively modified via functional alkoxysilanes, whereas etched silicon surfaces are unreactive. Using either a two‐step or a straight‐forward one‐step process employing commercially available chemicals, atom transfer radical polymerization (ATRP) initiator functions are attached selectively to the non‐etched surface areas, and subsequently used to polymerize either methyl methacrylate (MMA) or N‐isopropyl acrylamide (NIPAM) in a controlled surface‐initiated activator regenerated by electron transfer (ARGET)‐ATRP process. This procedure allows for the further self‐aligned functionalization of the micropatterned samples, enabling the production of highly functional, patterned surfaces, potentially suitable for applications in areas such as cell adsorption, microfluidics, or functional microsystems, e.g., MEMS.

Hemoglobin-catalyzed atom transfer radical polymerization for ultrasensitive electrochemical DNA detection

The use of hemoglobin (Hb) to drive atom transfer radical polymerization (ATRP) process (Hb-ATRP) for detection of lung cancer related nucleic acid is firstly reported. Hb does not need to be treated prior to using indicating the potential for synthetic engineering in complex biological microenvironments without the need for in vitro techniques. Here, we report a new signal amplification strategy using Hb-mediated graft of nitronyl niroxide monoradical polymers as a signal-on electrochemical biosensor for ultralow level DNA highly selective detection. Building DNA biosensors includes: (i) the fixation of peptide nucleic acid (PNA) probe (no phosphate group) via the 5′ terminus-SH; (ii) the modification of transition metal; (iii) Site-specific markers of Hb-ATRP promoter, and (iv) the grafting of polymers with electrochemical signal by Hb-ATRP process. Through the Hb-ATRP process of nitronyl nitroxide monoradical (TEMPO), the presence of a small amount of DNA can eventually result in calling a certain number of TEMPO redox tags. Obviously, the Hb-ATRP is a method of easy source of raw materials, simple operation and no need for complex equipment. The constructed biosensor, as expected, is highly selective and sensitive to target DNA. The detection limit can be calculated as 15.96 fM under optimal conditions. The excellent performance also shows that the constructed DNA biosensor is suitable for DNA screening and DNA concentration determination in complex sample matrix.

Experimental determination of activation rate constant and equilibrium constant for bromo substituted succinimide initiators for an atom transfer radical polymerization process

Abstract Alkyl bromides are used as initiators in most of the atom transfer radical polymerization (ATRP) process and play an important role for controlling the ATRP equilibrium. In this work, the effect of solvent on equilibrium constant of ATRP (K ATRP) and rate constant of activation (k act) of three isomeric alkyl bromides [namely, N-phenyl(3-bromo-3-methyl)succinimide, N-phenyl(3-bromo-4-methyl)succinimide, and N-phenyl(3-bromomethyl)succinimide] is reported. The k act and K ATRP values of alkyl bromide are determined experimentally using UV–Vis-NIR spectrometry. The termination rate constant for model compound is calculated using DOSY NMR spectroscopy. The k act and K ATRP values for the mentioned alkyl bromides are determined in five different polar solvent and the effect of polarity is observed. The obtained values of k act and K ATRP of N-phenyl(3-bromo-3-methyl)succinimide in acetonitrile at 25 °C is 6.60 × 10−2 L mol−1 s−1 and 1.42 × 10−9, respectively. These values are quite comparable with the experimentally determined reported k act and K ATRP of values of acrylates and benzyls initiators. Alternatively, the investigation of possible chain initiation activity for the ATRP process for the mentioned alkyl bromides is carried out theoretically using density functional theory (DFT) method [B3LYP/6-31+G(d) level]. A good correlation is obtained between the experimentally determined and theoretically calculated K ATRP values of studied alkyl bromides in chosen solvents. Significantly, it is found that the values of k act and K ATRP of alkyl bromides is solvent dependent and the magnitude values of the k act and K ATRP increases with increasing the solvent polarity. The proposed bromo substituted succinimides can be used as the initiator for the polymerization of acrylates, benzyls, maleimides, and itaconimides monomer under the selected solvent system.

Visible-Light Amine Thioxanthone Derivatives as Photoredox Catalysts for Photopolymerization Processes

Herein, mono- and disubstituted thioxanthones have been synthesized and introduced as photosensitizers of iodonium salt for cationic and free-radical photopolymerization of epoxy and an acrylate monomer, respectively. Photoinitiation activity of these molecules was verified during photopolymerization processes performed upon exposure to visible LEDs of 420, 455, and 470 nm. The kinetics of the photopolymerization processes was followed using FT-IR spectroscopy. Moreover, the developed compounds were proposed as strongly reducing metal-free photoredox catalysts in organocatalyzed atom transfer radical polymerization (ATRP). Thioxanthone derivatives (with alkyl halide) efficiently activate the ATRP of methyl methacrylate using a visible LED as an irradiation source. The formed polymers in the ATRP process were characterized by SEC. Apart from studying the photopolymerization processes with the participation of obtained thioxanthones, absorption, fluorescence, as well as electrochemical properties of thioxanthone derivatives were investigated. Furthermore, the performance of studied compounds in 3D printing applications was also examined. The most important result of this study is the design and possible application of photosensitizers/photocatalysts for photopolymerization processes.

Imine‐based covalent organic framework as photocatalyst for visible‐light‐induced atom transfer radical polymerization

AbstractPhotoinduced atom transfer radical polymerization (ATRP) is an economical and environment‐friendly method for synthesizing polymers with pre‐designable structures and precise molecular weight. Although significant progress for copper‐mediated photoinduced ATRP has been achieved, several drawbacks still remain, such as poor electron transfer capability and absorption bands of photocatalysts near UV region. Herein, imine‐based covalent organic framework, TAPPy‐TPA‐COF, has been synthesized as potential heterogeneous photocatalyst for photoinduced ATRP. The “living” feature of polymerizations of methyl methacrylate (MMA) can be well controlled by efficiency maintain the balance between activation and inactivation of CuI and CuII. The chain extension experiments have further demonstrated the chain‐end fidelity of polymers. Meanwhile, the catalyst recycle experiments have revealed stability of TAPPy‐TPA‐COF toward ATRP processes. These results support the feasibility of using COFs as heterogeneous photocatalysts for copper‐mediated ATRP under visible light irradiation.

Conjugated Cross-linked Phenothiazines as Green or Red Light Heterogeneous Photocatalysts for Copper-Catalyzed Atom Transfer Radical Polymerization.

Using the power of light to drive controlled radical polymerizations has provided significant advances in synthesis of well-defined polymers. Photoinduced atom transfer radical polymerization (ATRP) systems often employ UV light to regenerate copper activator species to mediate the polymerization. Taking full advantage of long-wavelength visible light for ATRP would require developing appropriate photocatalytic systems that engage in photoinduced electron transfer processes with the ATRP components to generate activating species. Herein, we developed conjugated microporous polymers (CMP) as heterogeneous photocatalysts to exploit the power of visible light in promoting copper-catalyzed ATRP. The photocatalyst was designed by cross-linking phenothiazine (PTZ) as a photoactive core in the presence of dimethoxybenzene as a cross-linker via the Friedel-Crafts reaction. The resulting PTZ-CMP network showed photoactivity in the visible region due to the extended conjugation throughout the network because of the aromatic groups connecting the PTZ units. Therefore, photoinduced copper-catalyzed ATRP was performed with CMPs that regenerated activator species under green or red light irradiation to start the ATRP process. This resulted in efficient polymerization of acrylate and methacrylate monomers with high conversion and well-controlled molecular weight. The heterogeneous nature of the photocatalyst enabled easy separation and efficient reusability in subsequent polymerizations.

Enhancing the efficiency of semiconducting quantum dot photocatalyzed atom transfer radical polymerization by ligand shell engineering.

Manipulating the ligand shell of semiconducting quantum dots (QDs) has proven to be a promising strategy to enhance their photocatalytic performance for small molecule transformations, such as H2 evolution and CO2 reduction. However, ligand-controlled catalysis for macromolecules, which differ from small molecules in penetrability and charge transfer behavior due to their bulky sizes, still remains undiscovered. Here, we systematically investigate the role of surface ligands in the photocatalytic performance of cadmium selenide (CdSe) QDs in light-induced atom transfer radical polymerization (ATRP) by using thiol-based ligands with various polarities and chain lengths. A highly enhanced polymerization efficiency was observed when 3-mercapto propionic acid (MPA), a short-chain and polar ligand, was used to modify the CdSe QDs' surface, achieving high chain-end fidelity, good temporal control, and a dispersity of 1.18, while also tolerating a wide-range of functional monomers ranging from acrylates to methacrylates and fluorinated monomers. Transient absorption spectroscopy and time-resolved photoluminescence studies reveal interesting mechanistic details of electron and hole transfers from the excited QDs to the initiators and 3-MPA capping ligands, respectively, providing key mechanistic insight of these ligand controlled and QD photocatalyzed ATRP processes. The thiolate ligands were found to serve as an efficient hole acceptor for QDs, which facilitates the formation of a charge-separated state, followed by electron transfer from the conduction band edge to initiators and ultimately suppressing charge recombination within the QD.

Synthesis and properties of rosin grafted polymers via “grafting from” ATRP: The role of rosin-based initiator

Rosin is an important renewable resource. However, preparation of rosin-based polymers with good performance is still challenging. In this work, a series of rosin-based polymers were prepared via “grafting from” atom transfer radical polymerization (ATRP) using dehydroabietic acid (DA, extracted from pine trees) derived ATRP initiator (2-BriBEDA, (2-bromoisobutyric) hydroxyethyl ester of dehydroabietic acid). The graft polymerization behavior of polar monomer methyl methacrylate (MMA), nonpolar monomer lauryl methacrylate (LMA) from DA were investigated. The kinetic studies showed that the ATRP processes of MMA, LMA as well as MMA-co-LMA were all living and controlled, which indicated that 2-BriBEDA was a good ATRP initiator. With the introduction of DA, all rosin-based copolymers showed improved thermal stability, UV-blocking performance, hydrophobicity and mechanical properties. In addition, DA-g-P(MMA-co-LMA) polymers showed good mechanical and elastic properties with highest tensile strength of 5.10 ± 0.87 MPa and strain of 513 ± 32 % and elastic strain recovery above 70 % which was comparable with other reported sustainable thermoplastic elastomers (TPEs) polymers. This work demonstrates an alternative avenue for rosin-based polymer design to achieve the improvement in thermal, UV-blocking and mechanical performance.

Electrochemistry for Atom Transfer Radical Polymerization.

Atom Transfer Radical Polymerization (ATRP) is the most powerful and most employed technology of Controlled Radical Polymerization (CRP) to produce polymers with well-defined architecture, that is, composition, topology, and functionality. Several hundreds of papers are published every year on ATRP processes, mainly based on empiric experimental procedures. Electrochemistry powerfully entered in the field of ATRP about 10 years ago, providing important contributions both to the further development of the process and to a better understanding of its mechanism. Five main issues took advantage of electrochemistry and/or its synergism with ATRP: i) understanding the mechanism of ATRP activation; ii) determination of thermodynamic parameters; iii) determination of activation and deactivation rate constants; iv) the SARA ATRP vs SET-LRP dispute: the role of Cu0 ; v) electrochemically-mediated ATRP.

Regenerative magnetic nanoparticle-supported ATRP ligand for bottlebrush copolymer preparation

A facile method is proposed to prepare functionalized Fe3O4@Me6TREN nanoparticles (NPs) for atom transfer radical polymerization (ATRP). The Me6TREN moieties on NPs surface can bind copper, thus making them effective nano ligands for ATRP reactions to synthesize bottlebrush copolymers. After polymerization, purification of the polymer achieved only by a magnet, is much simpler than traditional ATRP process. No column chromatography is required. Furthermore, Fe3O4@Me6TREN NPs can thus be regenerated via separating copper from NPs surface by ligand exchange with EDTA-Na2. Such a versatile nano ligand is of great worth to promote the industrial application of ATRP at a large scale and low cost.

PH and temperature-responsive POSS-based poly(2-(dimethylamino)ethyl methacrylate) for highly efficient Cr(VI) adsorption

Sixteen-arm star-shaped polymer of s-POSS-(PDMAEMA)16 was synthesized by octakis(dibromoethyl) polyhedral oligomeric silsesquioxane (POSS-(Br)16) initiating 2-(dimethylamino)ethyl methacrylate (DMAEMA) via atom transfer radical polymerization (ATRP) process. The obtained s-POSS-(PDMAEMA)16 showed controllable and reversible pH-responsive behavior at pH = 1–12 and thermoresponsive behavior at 20–60 °C. Typical core/shell micelles (100–130 nm) were formed by s-POSS-(PDMAEMA)16 at pH = 7.8 and transformed into 450–600 nm snowflake-shaped micelles at pH = 6, 400 nm butterfly-shaped micelles at pH = 3, and 20–40 nm spherical particles at pH = 10 due to the different interactions between the PDMAEMA chains and the aqueous solution. When the pH of the solution decreased from 10 to 3, 350–400 nm butterfly-shaped micelles were reformed, demonstrating the reversibility of this process. The soluble-insoluble transition temperature for s-POSS-(PDMAEMA)16 was located between 20 and 60 °C. Furthermore, equilibrium adsorption indicated that s-POSS-(PDMAEMA)16 could adsorb Cr(VI) due to strong electrostatic interactions between its tertiary amines and Cr(VI).

Spatial modulation of biomolecules immobilization by fabrication of hierarchically structured PEG-derived brush micropatterns: An versatile cellular microarray platform

Microarray technology holds enormous promise in the development of various fields ranging from tissue engineering, regenerative medicine to high-throughput screening. Here, based on the digital micromirror device (DMD)-based spatiotemporal regulation of surface-initiated photoinduced atom transfer radical polymerization (Photo-ATRP) process, a flexible and versatile methodology was developed to fabricate a hierarchical microarray structure constituted with a homogeneous hyperbranched polyethylene glycol (PEG)-derived brush layer as anti-fouling background and an extension layer of square-grid poly(2-(2-azido-2-methyl-1-oxopropoxy) ethyl methacrylate) (PAMEMA) brushes micropatterns on the silicon substrate. The terminal azido groups on the side chains of PAMEMA brushes provide abundant reactive sites to realize the covalent immobilization of target biomolecules, including RGD peptide, fibronectin, BSA and streptavidin. The TOF-SIMS and fluorescence characterizations demonstrated the feasibility and efficiency of spatially modulating the density of surface-bound biomolecules through regulating the 3D architecture parameters of the PAMEMA brush micropatterns and consequentially the azido chemical functionality. Moreover, culture experiments of human bone-derived marrow stromal cells (BMSCs) and mouse L929 cells were conducted on the obtained hierarchical microarray structure in a high-throughput manner. The presented hierarchical microarray structure holds excellent potential as a high-throughput screening platform, allowing for the parallel assessment of cell-surface interactions.

Shape Shifting of Cup Shaped Particles on Growing poly (2‐hydroxy ethyl methacrylate) Brushes by “Grafting From” Approach and Dissipative Particle Dynamics Simulation

AbstractControlled bending leading to shape shifted microparticles is indispensable for the targeted biomedical applications including advanced drug/cell delivery and has been one of the major research components in biomedical area for decades. Here, we report the shape‐shifting of cup‐shaped particles created by electrojetting from a blend of biodegradable polylactide (PLA) and biocompatible co‐polymer (poly[methylmethacrylate‐co‐2‐(2‐bromopropionyloxy)ethyl methacrylate] (poly(MMA‐co‐BEMA))) containing ATRP (Atom Transfer Radical Polymerization) initiating moiety, at a ratio of 75:25. Surface initiated ATRP of HEMA (2‐hydroxy ethyl methacrylate) was carried out for 1 hour to immobilize self‐crosslinkable poly(HEMA) brushes onto the cup shaped particles which underwent controlled bending post polymer brush growth leading to the formation of spherical ball with one small opening (hole). However, no change of shape was observed while growing non‐crosslinkable hydrophilic poly(DMAEMA) (poly(2‐(Dimethylamino)ethyl methacrylate)) brush from the surface of cup shaped particles. To understand the underlying phenomena of shape shifting, simulation studies were also performed. Dissipative particle dynamics (DPD) simulation of the ATRP process at the cup surface further confirmed that the use of HEMA monomer indeed led to the desired compact modified structure of the cup particle due to the crosslinking connectivity across the interface. We have also calculated the radial distribution function (RDF) and radius of gyration to study the structure of modified particles.

High adsorption of fulvic acid by amino modified styrene-type macroporous resin and evaluation of its mechanism.

Amino-modified HPD 100 styrene-type macroporous resin (M-HPD 100) was successfully synthesized by the atom transfer radical polymerization process. The modified resin showed excellent performance in the degradation of fulvic acid (FA). FA removal was pH, temperature and flow velocity dependent. The adsorption data could be well interpreted by the Freundlich model. The maximum adsorption efficiency for M-HPD 100 obtained from the Freundlich model was 92.5% at 298 K, which was 37% higher than that of unmodified styrene-type macroporous resin (HPD 100). The adsorption process could be described by the pseudo-second-order kinetic model. The intra-particle diffusion and film diffusion were believed to be the rate-limiting process for both adsorbents. Thermodynamic parameters suggested it was a multi-layer physicochemical process. More importantly, although limited improvements were seen, the results of this study suggested that the surface of resin can be modified with functional groups to enhance the adsorption of FA from aqueous solution and may give other advantages; for example, despite the interference of the pore diffusion coefficient and other substances, M-HPD 100 has excellent regeneration capacity, and the adsorption and desorption efficiency was 74% and 64.28% respectively after six regenerations, which proved it has engineering application value.

Photocatalytic, fluorescent BiPO4@Graphene oxide based magnetic molecularly imprinted polymer for detection, removal and degradation of ciprofloxacin.

Herein, we have developed a photocatalytic, fluorescent bismuth phosphate@graphene oxide (BiPO4@GO) based magnetic nano-sized-molecularly imprinted polymer (MMIP) for detection, removal, and degradation of ciprofloxacin (CIP) via atom transfer radical polymerization (ATRP) process. CIP is a very popular antibiotic, but their heavy doses in recent time, made them an environmental threat. The imprinted polymer was synthesized using N-vinyl caprolactam, N, N-methylene bis-acrylamide, ZnFe2O4 nanoparticle, and Bi(PO4)@GO as a biocompatible monomer, crosslinker, magnetic moiety, and photocatalyst, respectively. The characterization of the molecularly imprinted polymer was systematically evaluated by electrochemical techniques, X-ray diffraction, fluorescence spectroscopy, scanning electron microscopy, etc. The prepared BiPO4@GO modified CIP-imprinted magnetic polymer (BiPO4@GO-MMIPs) shows high selectivity towards their template/target analyte (i.e., CIP) and used for their visual (via fluorescence study) and trace level detection (via the electrochemical study) in various kind of complex matrix. The dual behaviour i.e. electrochemical and optical sensing of CIP was successfully achieved in a good linear range of 39.0 to 740.0μgL-1 with detection of limit (LOD) of 0.39μgL-1 for electrochemical study and 39.0 to 328.0μgL-1 and LOD of 0.40μgL-1 for optical study. The prepared BiPO4@GO-MMIPs were successfully used for the detection of CIP from complex matrix like blood serum, whole blood, and milk sample as well as removal and degradation of CIP with good efficiency.

One-Pot Synthesis of Star Copolymers by the Combination of Metal-Free ATRP and ROP Processes.

A completely metal-free strategy is demonstrated for the preparation of star copolymers by combining atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP) for the syntheses of block copolymers. These two different metal-free controlled/living polymerizations are simultaneously realized in one reaction medium in an orthogonal manner. For this purpose, a specific core with functional groups capable of initiating both polymerization types is synthesized. Next, vinyl and lactone monomers are simultaneously polymerized under visible light irradiation using specific catalysts. Spectral and chromatographic evidence demonstrates the success of the strategy as star copolymers are synthesized with controlled molecular weights and narrow distributions.

High retreatability and dimensional stability of polymer grafted waterlogged archaeological wood achieved by ARGET ATRP

To explore new methods to maintain the dimensional stability of waterlogged archaeological wood after drying and keep the natural cell lumens unaltered for future retreatments, activator regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) is employed to consolidate archaeological wood. To prepare the ATRP process, the waterlogged archaeological wood samples (Pinus massoniana with maximum moisture content of around 529%) were first modified by 2-bromoisobutyryl bromide in CH2Cl2 to acquire C-Br bonds as initiators. Then, butyl methacrylate or styrene was polymerized to the remaining cell walls with catalyst (CuBr2), reductant (ascorbic acid) and ligand (PMDETA) in ethanol. After the treatment, the samples were washed and naturally dried. The results characterized by microscopy showed that the polymerization only took place within the remaining cell walls, showing no sign of collapse or distortion after air drying, and all natural cell lumens could be retained for future retreatments. Also, anti-shrinkage efficiencies as high as 87.8% for the wood sample grafted with polystyrene and 98.5% for the wood sample grafted with polybutylmethacrylate were obtained from the treatment described in this paper, indicating modification of grafting polymer through ARGET ATRP can help maintain the dimensional stability of water archaeological wood effectively.