Free Atom Transfer Radical Polymerization Research Articles

Features of Methyl Methacrylate Polymerization Mediated by Methylene Blue and Ethyl 2-Bromoisobutyrate under Photoirradiation Conditions

Using methyl methacrylate polymerization as an example, the features of polymer synthesis in the presence of the catalytic system [methylene blue + ethyl 2-bromoisobutyrate] at room temperature under visible light irradiation are investigated. The effect of polymerization conditions, including the light irradiation wavelength and various structure activators, on the monomer conversion and molecular weight characteristics of polymers is estimated. It is shown that polymerization can proceed in the controlled mode under mild temperature conditions according to the atom transfer mechanism (Metal Free Atom Transfer Radical Polymerization) to high conversions at low photocatalyst concentrations.

Preparation of coumarin polymer grafted nanocellulose films to form high performance, photoresponsive barrier layers

AbstractHydrophobically modified cellulose is prepared in this research by conducting atom transfer radical polymerization (ATRP) of methacrylate substituted coumarin monomer on initiator grafted cellulose. The photocrosslinking of uniformly grafted coumarin on cellulose surface is applied to improve the water vapor barrier property of the film. The water vapor transmission rate (WVTR) of films prepared from modified cellulose with varying grafting density, grammage, and photocrosslinking time is studied. By increasing the amount of crosslinking within the grafted cellulose film, we succeeded in reducing WVTR. The WVTR is reduced from 160 to 20 g/m2/day using a sheet of 60 g/m2 after crosslinking. The effect of grafting density on WVTR is also analyzed to observe that the higher the grafting density, lower the WVTR of the sheet both before and after crosslinking. Furthermore, free ATRP polymerization (without cellulose) and polymerization using a sacrificial initiator of the monomer are conducted to estimate the dispersity of the polymer on cellulose. The monomer, free polymer and cellulose grafted polymers are analyzed for the composition, thermal, morphology, photoresponsive behavior, and polymerization quantification using NMR, FTIR, UV–Vis, TGA DSC, GPC, SEM, ICP‐MS. It is concluded that the inter and intramolecular photo dimerization of coumarin molecules forms a hydrophobic crosslinked hyper network in the polymer sheet, which improves its barrier property.

Visible light‐driven acridone catalysis for atom transfer radical polymerization

AbstractAcridone as a new kind of visible light photocatalyst has been developed to catalyze metal free atom transfer radical polymerization (ATRP). The photocatalyst possess low excited state potential as can undergo an oxidative quenching pathway to initiate ATRP of vinyl monomers. Kinetic study and light on/off reaction demonstrate the “living”/controlled nature of the polymerization by light. Block copolymers can be achieved by using PMMA as macroinitiator to reinitiate polymerization of other vinyl monomers, which shows highly preserved Br chain‐end functionality in the synthesized polymers. Moreover, the polymerization can be conducted under air atmosphere as most photocatalysts need anaerobic condition, which may give inspiration of further application of this kind of photocatalyst.

Li6.4La3Zr1.4Ta0.6O12/Star-Shaped Hybrid Polyhedral Oligomeric Cage Silsesquioxane Polymer Composite Electrolytes for All-Solid-State Lithium Metal Batteries

The low ionic conductivity and mechanical strength are important factors impeding the application of solid polymer electrolytes. Herein, we design synthesize an organic/inorganic hybrid star-shaped polymer of octa(poly(methyl methacrylate)–poly(poly(ethylene glycol) methyl ether methacrylate) cage oligomeric silsesquioxanes (POSS–(PMMA–PPEGMEM)8) by one-step free atom transfer radical polymerization (ATRP), and compound with Li6.4La3Zr1.4Ta0.6O12 (LLZTO) to prepare a composite polymer electrolyte membrane (LP-CPEM). The star-shaped structure of the POSS–(PMMA–PPEGMEM)8 induced by octachloropropyl polyhedral cage oligomeric silsesquioxane (OCP-POSS) is beneficial to reduce the crystallinity of polymer and increase the movement of the polymer chain to form a continuous interconnected ion migration channel. The LLZTO fillers in the LP-CPEM could simultaneously hinder the orderly arrangement of polymer chains and provide other ion transport paths to increase the ion conductivity of LP-CPEM. The LP-CPEM with 7.5 wt % LLZTO has higher ionic conductivity of 3.8 × 10–4 S cm–1 at 30 °C and high mechanical strength (5.2 MPa). Additionally, Li/Li symmetric cells demonstrate stable constant current charging/discharging during 1000 h at 0.1 mA cm–2, and the all-solid-state batteries fabricated by the LP-CPEM exhibit good cyclic stability. It is promising for the development of next-generation high-safety all-solid-state lithium metal batteries.

Synthesis of amphiphilic star-shaped block copolymers through photo-induced metal free atom transfer radical polymerization

Photo-induced metal free ATRP method was employed for the synthesis of star-shaped polymers. By using 21-Br-β-CD as the macroinitiator, 10-phenylphenothiazine as the photoredox catalyst, star-shaped PtBA homopolymers were synthesized. The photo-induced ATRP displayed all the characteristics of controlled/living polymerization systems and the good light control over the polymerization process. The successful chain extension with MMA demonstrated the high livingness of PtBA “arms” and good controllability of the Photo-induced metal free ATRP. Finally, the achieved PtBA-b-PMMA star-shaped copolymers were used as templates for the preparation of precisely size-tunable CdSe quantum dots after a simple hydrolyzing process.

Organocatalyzed atom transfer radical polymerization (ATRP) using triarylsulfonium hexafluorophosphate salt (THS) as a photocatalyst

Triarylsulfonium hexafluorophosphate salt (THS), an organic and inexpensive compound, was employed as a photocatalyst for metal free atom transfer radical polymerization (ATRP) of methacrylate monomers.

Advances in Organocatalyzed Atom Transfer Radical Polymerization

Atom transfer radical polymerization (ATRP) is one of the most robust tools to prepare well-defined polymers with precise topologies and architectures. Although series of improved ATRP methods have been developed to decrease the metal catalyst loading to parts per million, metal residue is the key limiting factor for variety of applications, especially in microelectronic and biomedical area. The feasible solution to this challenge would be the establishment of metal-free ATRP. Since 2014, organocatalyzed ATRP (O-ATRP) or metal free ATRP has achieved significant progress by developing kinds of organic photoredox catalysts. This review highlights the advances in organocatalyzed atom transfer radical polymerization as well as the potential future directions.

Phenothiazine 유래 유기광촉매을 이용한 Metal Free 원자이동 라디칼 중합

Phenothiazine 유래 유기광촉매을 이용한 Metal Free 원자이동 라디칼 중합

Photo‐mediated metal free atom transfer radical polymerization of acrylamide in water

ABSTRACTPhoto‐mediated metal free atom transfer radical polymerization of acrylamide was conducted at 25 °C in water under visible light irradiation with water soluble 2‐hydroxy‐3‐(4‐benzoylphenoxy)‐N,N,N‐trimethyl‐1‐propaminium chloride (HBTPC) as photoredox catalyst and 2‐hydroxyethyl 2‐bromoisobutyrate as alkyl halide. The polymerization followed first‐order reaction kinetics. The living character of photo‐mediated atom transfer radical polymerization of acrylamide was verified by the linear development of the polymer number average molar mass (Mn,GPC) with monomer conversion and narrow molecular weight distributions (Đ). The effects of acrylamide concentration, light intensity, amount of HBTPC, and tris(2‐dimethylaminoethyl)amine on polymerization were investigated. Increasing monomer concentration led to a higher Mn,GPC values with narrow Đ. The polymerization rate increased with increasing the amount of monomer, light intensity, HBTPC and tris(2‐dimethylaminoethyl)amine. The polymerization was monitored by the periodic light on/off. The structure of polyacrylamide was analyzed by proton nuclear magnetic resonance spectrometer and gel permeation chromatography. Successful chain extension experiments show the controlled nature of the polymerization. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46567.

Fabrication of Reduction-Sensitive Amphiphilic Cyclic Brush Copolymer for Controlled Drug Release.

The cyclic brush polymers, due to the unique topological structure, have shown in the previous studies higher delivery efficacy than the bottlebrush analogues as carriers for drug and gene transfer. However, to the best of knowledge, the preparation of reduction-sensitive cyclic brush polymers for drug delivery applications remains unexplored. For this purpose, a reduction-sensitive amphiphilic cyclic brush copolymer, poly(2-hydroxyethyl methacrylate-g-poly(ε-caprolactone)-disulfide link-poly(oligoethyleneglycol methacrylate)) (P(HEMA-g-PCL-SS-POEGMA)) with reducible block junctions bridging the hydrophobic PCL middle layer and the hydrophilic POEGMA outer corona is designed and synthesized successfully in this study via a "grafting from" approach using sequential ring-opening polymerization (ROP) and atom transfer free radical polymerization (ATRP) from a cyclic multimacroinitiator PHEMA. The resulting self-assembled unimolecular core-shell-corona (CSC) micelles show sufficient salt stability and efficient destabilization in the intracellular reducing environment for a promoted drug release toward a greater therapeutic efficacy relative to the reduction-insensitive analogues. The overall results demonstrate the reducible cyclic brush copolymers developed herein provides an elegant solution to the tradeoff between extracellular stability and intracellular high therapeutic efficacy toward efficient anticancer drug delivery.

A new method in designing compatibility and adhesion of EVA/PMMA blend by using EVA-g-PMMA with controlled graft chain length

Atom transfer free radical polymerization (ATRP) was employed in a synthesis of graft polymer EVA-g-PMMA with controlled length of side PMMA chains. Three steps of synthesis: partial hydrolysis of EVA, esterification with chloroacetyl chloride and ATRP grafting were performed to produce EVAOH, macroinitiator EVACl and grafted polymers G8020 (EVA/PMMA = 80/20 wt%) and G6040 (EVA/PMMA = 60/40 wt%). FTIR, Raman and NMR spectroscopy were used in the determination of the chemical structure and modification of EVA. Transmitted light and dark field microscopy showed higher affinity for coil formation of EVA-g-PMMA with longer PMMA side chains, i.e. G6040 compatibilizer. Morphological, thermal and adhesive properties of optical fiber adhesives of graft polymers and polymer blends poly(ethylene-co-vinyl acetate)-blend-poly(methyl methacrylate) (EVA/PMMA) compatibilized with 1 wt% of EVA-g-PMMA, were studied. Image analysis of SEM micrographs showed effective compatibilization with short grafted chains (G8020) that was indicated by lower porosity characteristics. TG/DTG analysis enabled determination of degree of hydrolysis and amount of chloro-functionalized groups. DSC analysis showed higher thermal stability of G8020 polymer. Single lap joint of adhesives/optical fibers were subjected to adhesive testing and obtained results for maximal force applied and adhesive failure suggested the visible influence of the length of graft chains on adhesion.

Fabrication of Thermosensitive Cyclic Brush Copolymer with Enhanced Therapeutic Efficacy for Anticancer Drug Delivery.

Adaptation of cyclic brush polymer for drug delivery applications remains largely unexplored. Herein, cyclic brush copolymer of poly(2-hydroxyethyl methacrylate-g-poly(N-isopropylacrylamide-st-N-hydroxyethylacrylamide)) (cb-P(HEMA-g-P(NIPAAm-st-HEAAm))), comprising a cyclic core of PHEMA and thermosensitive brushes of statistical copolymer of P(NIPAAm-st-HEAAm), is designed and synthesized successfully via a graft-from approach using atom transfer free radical polymerization from a cyclic multimacroinitiator. The composition of the brush is optimized to endow the resulting cyclic brush copolymer with a lower critical solution temperature (LCST) slightly above the physiological temperature, but lower than the localized temperature of tumor tissue, which is suitable for the hyperthermia-triggered anticancer drug delivery. Critical aggregation concentration determination reveals better stability for the unimolecular nanoparticle formed by the cyclic brush copolymer than that formed by the bottlebrush analogue. The dramatically increased size with elevated temperatures from below to above the LCST confirms hyperthermia-induced aggregation for both formulations. Such structural destabilization promotes significantly the drug release at 40 °C. Most importantly, the drug-loaded cyclic brush copolymer shows enhanced in vitro cytotoxicity against HeLa cells than the bottlebrush counterpart. The better stability and higher therapeutic efficacy demonstrates that the thermosensitive cyclic brush copolymer is a better formulation than bottle brush copolymer for controlled drug release applications.

ATRP Fabricated and Short Chain Polyethylenimine Grafted Redox Sensitive Polymeric Nanoparticles for Codelivery of Anticancer Drug and siRNA in Cancer Therapy.

To overcome the limitations of conventional chemotherapy, nanoparticle-mediated combinatorial delivery of siRNA and drugs represents a new approach to overcome its associated side effects. Designing safe and efficient vehicles for their codelivery has emerged as a potential challenge in the clinical translation of these formulations. Herein, we have demonstrated a novel "two-in-one" polyplex nanosystem developed from redox sensitive, short chain polyethylenimine modified poly[(poly(ethylene)glycol methacrylate]-s-s-polycaprolactone copolymer synthesized by atom-transfer free-radical polymerization (ATRP), which can deliver doxorubicin and polo-like kinase I (plk1) siRNA, simultaneously for an enhanced chemotherapeutic effect. The nanoparticles were found to be stable at physiological buffer with and without fetal bovine serum (FBS). The developed polymeric nanosystem was found to be biocompatible and hemocompatible in vitro and in vivo at repeated dose administrations. The polymer could easily self-assemble into ∼100 nm spherical nanoparticles with enhanced doxorubicin loading (∼18%) and effective siRNA complexation at a polymer to siRNA weight ratio of 15. The doxorubicin loaded nanoparticles exhibited ∼4-fold higher drug release in endosomal pH (pH 5) containing 10 mmol of GSH compared to pH 7.4, depicting their redox-sensitive behavior. The polyplexes were capable of delivering both cargos simultaneously to cancer cells in vitro as observed by their excellent colocalization in the cytoplasm of MDA-MB-231 and HeLa cells using confocal laser microscopy. Moreover, in vitro transfection of the cells with polyplexes exhibited 50-70% knockdown of plk1-mRNA expression in both cell lines. In vivo administration of the drug loaded polyplexes to EAT tumor bearing (EAT, Ehrlich ascites tumor) Swiss albino mice showed a ∼29-fold decrease in percent tumor volume in comparison to the control group. The results highlight the therapeutic potential of the polyplexes as a combined delivery of doxorubicin and plk1-siRNA in cancer therapy.

Organoboron-Based Photochromic Copolymers for Erasable Writing and Patterning

We report herein the first examples of organoboron-based photochromic polymers. The synthesis of a series of blue fluorescent random copolymers bearing photochromic boron repeating units, poly[(6-B(ppy)Mes2)oxyhexyl methacrylate)m-r-(tert-butyl methacrylate)n], ppy = 2-phenylpyridyl and Mes = mesityl, via atom transfer free radical polymerization (ATRP) has been accomplished. These new polymers display thermally reversible photochromism, switching color from colorless to deep blue, and fluorescence from bright sky blue to deep blue. By controlling the monomer ratio, the photoisomerization quantum efficiencies of the polymers can be tuned effectively. In addition, the number of boron units in the polymer has been found to have a significant impact on fluorescence quenching efficiency. The new organoboron-based polymers can be used effectively as a switchable/erasable ink on glass or paper substrate or for creating switchable/erasable patterns as neat polymer films.

Surface polyPEGylation of Eu3+ doped luminescent hydroxyapatite nanorods through the combination of ligand exchange and metal free surface initiated atom transfer radical polymerization

The Eu3+ doped luminescent hydroxyapatite (HAp) nanorods with uniform size and morphology can be synthesized by hydrothermal route. However, these HAp nanorods are coated by hydrophobic oleylamine, which makes them difficult to be dispersed in aqueous solution and impede their biomedical applications. In this work, Eu3+ doped luminescent polymers functionalized HAp nanorods were prepared through the combination of ligand exchange reaction and metal free surface initiated atom transfer radical polymerization (ATRP) method. In this procedure, the amino group functionalized HAp nanorods were first prepared by ligand exchange reaction using adenosine monophosphate (AMP) as ligand. Then the Br-containing initiators (HAp-Br) were introduced onto the surface of HAp-AMP nanorods through the amidation reaction. Finally, polymers functionalized HAp nanorods were prepared by metal free ATRP method using poly(ethylene glycol) methacrylate (PEGMA) as monomer and 10-phenylphenothiazine (PTH) as organic photocatalyst. The properties of these obtained HAp nanocomposites (HAP-polyPEGMA nanorods) were characterized by means of transmission electron microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis in detail. The cell imaging of these HAP-polyPEGMA nanorods was examined using laser scanning confocal microscope to evaluate their biomedical applications. We demonstrated for the first time that hydrophobic luminescent HAp nanorods can be functionalized with polyPEGMA through the combination of ligand exchange reaction and metal free surface initiated ATRP. As compared with the traditional ATRP, the metal free ATRP can overcome the toxic and fluorescence quenching effects of metal catalysts such as copper ions. More importantly, the strategy described in this work should also be utilized for fabrications of many other luminescent polymer nanocomposites due to its good monomer adoptability.

Interaction of bioactive compounds on capillary inner surfaces bearing a dense thermoresponsive polymer brush

To confirm the modification of a dense thermoresponsive polymer brush on a silica surface by surface-initiated (SI) atom transfer radical polymerization (ATRP), poly(N-isopropylacrylamide) (PNIPAAm) was polymerized from a free ATRP initiator and an ATRP initiator immobilized silica particle (SiP) via ATRP under various initiator concentrations. The obtained PNIPAAm exhibited a well-controlled molecular weight and modification of the concentrated PNIPAAm brush on the SiP surface was confirmed. Based on the optimal ATRP conditions, the PNIPAAm- and poly(NIPAAm-co-butyl methacrylate [BMA]) (PIB)-grafted capillary lumen were prepared by SI-ATRP and used as capillary columns for micro high-performance liquid chromatography for the modulation of biomolecular interactions. The hydrophobic interactions of steroids on the thermoresponsive polymer brush grafted capillary lumens increased with increasing polymer length above the lower critical solution temperature for each polymer. In addition, an increase in the retention factor of steroids with the PIB-grafted capillary began at lower temperatures than that observed for the PNIPAAm-grafted capillary. Thus, the separation of steroids was achieved using a stepwise temperature gradient and was enhanced by modulating the aqueous eluent flow rate during thermoresponsive capillary chromatography. These results indicated that the chain lengths of the concentrated thermoresponsive polymer brushes on the capillary lumen have a crucial influence on the interaction and separation of bioactive compounds in an aqueous mobile phase.

Morphometric study of proximal femur in post-menopausal women: A radiological study

Novel imidazoline-functionalized diblock copolymers based on polystyrene (PS) and poly(D,L-lactide) (PLA) were synthesized as precursors to corresponding functional PS-based porous materials through a three-step sequential methodology starting from an asymmetric heterobifunctional initiator. α-Hydroxyl poly(4-cyanostyrene-co-styrene) random copolymers were first obtained via an atom transfer free-radical polymerization (ATRP) procedure by varying the amount of 4-cyanostyrene in the comonomer feed. Cyano groups were then transformed into corresponding imidazoline rings. Subsequently, the microwave-assisted ring-opening polymerization (ROP) of d,l-lactide from the imidazoline-functionalized PS-based macroinitiators allowed for the generation of semi-degradable diblock copolymers with different PLA volume fractions so as to develop microphase-separated morphologies. The precursors and resulting copolymers were analyzed by 1H, 13C NMR, and FT-IR spectroscopy. Upon induced shear-flow via channel-die processing, oriented materials constituted of PLA nanodomains in a polystyrene-based continuous matrix were formed. Hydrolysis in alkaline conditions of the PLA sacrificial block yielded imidazoline-functionalized porous PS-based matrices. The resulting porous frameworks were analyzed by scanning electron microscopy (SEM) and nitrogen sorption porosimetry.

Surface modification of nanodiamond through metal free atom transfer radical polymerization

Surface modification of nanodiamond (ND) with poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] has been achieved by using metal free surface initiated atom transfer radical polymerization (SI-ATRP). The ATRP initiator was first immobilized on the surface of ND through direct esterification reaction between hydroxyl group of ND and 2-bromoisobutyryl bromide. The initiator could be employed to obtain ND-poly(MPC) nanocomposites through SI-ATRP using an organic catalyst. The final functional materials were characterized by 1H nuclear magnetic resonance, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermo gravimetric analysis in detailed. All of these characterization results demonstrated that ND-poly(MPC) have been successfully obtained via metal free photo-initiated SI-ATRP. The ND-poly(MPC) nanocomposites shown enhanced dispersibility in various solvents as well as excellent biocompatibility. As compared with traditional ATRP, the metal free ATRP is rather simple and effective. More importantly, this preparation method avoided the negative influence of metal catalysts. Therefore, the method described in this work should be a promising strategy for fabrication of polymeric nanocomposites with great potential for different applications especially in biomedical fields.

A new route toward imidazoline-functionalized porous polymeric materials from corresponding polystyrene-polylactide diblock copolymers

Novel imidazoline-functionalized diblock copolymers based on polystyrene (PS) and poly(D,L-lactide) (PLA) were synthesized as precursors to corresponding functional PS-based porous materials through a three-step sequential methodology starting from an asymmetric heterobifunctional initiator. α-Hydroxyl poly(4-cyanostyrene-co-styrene) random copolymers were first obtained via an atom transfer free-radical polymerization (ATRP) procedure by varying the amount of 4-cyanostyrene in the comonomer feed. Cyano groups were then transformed into corresponding imidazoline rings. Subsequently, the microwave-assisted ring-opening polymerization (ROP) of d,l-lactide from the imidazoline-functionalized PS-based macroinitiators allowed for the generation of semi-degradable diblock copolymers with different PLA volume fractions so as to develop microphase-separated morphologies. The precursors and resulting copolymers were analyzed by 1H, 13C NMR, and FT-IR spectroscopy. Upon induced shear-flow via channel-die processing, oriented materials constituted of PLA nanodomains in a polystyrene-based continuous matrix were formed. Hydrolysis in alkaline conditions of the PLA sacrificial block yielded imidazoline-functionalized porous PS-based matrices. The resulting porous frameworks were analyzed by scanning electron microscopy (SEM) and nitrogen sorption porosimetry.

Hierarchical porous molecule/ion imprinted polymers with double specific binding sites: Combination of Pickering HIPEs template and pore-filled strategy

To recognize and remove targeted organic and inorganic pollutants simultaneously, a simple and outstanding approach was provided to fabricate hierarchical porous molecule/ion imprinted polymers (M-IIPs) with double specific binding sites, Firstly, λ-cyhalothrin (LC) molecules imprinted polymer foam initiators (MIPFIs) with the average void diameter of 8.0μm were prepared via a W/O Pickering high internal phase emulsions (HIPEs) template stabilized by vinyl-silica particles (V-SPs). Secondly, based on a pore-filled strategy, adjustable amounts of copper ions (Cu(II)) imprinted polymers (IIPs) were incorporated into the macroporous surface of MIPFIs via atom transfer free radical polymerization (ATRP). Owing to the well-defined hierarchical porous structure, M-IIPs possessed enhanced binding kinetics, and the maximum monolayer adsorption capacities of as-prepared M-IIPs were 193.1μmolg−1 and 169.9μmolg−1 towards LC and Cu(II), respectively. The imprinting factor ε was 1.942 for LC, while their relative selectivity coefficients αr for Cu(II)/Zn(II) and Cu(II)/Ni(II) were 6.31 and 4.24 times higher than those of non-imprinted polymers (N-NIPs), illustrating that M-IIPs showed excellent molecular recognition in testing solutions. In the binary solution of LC and Cu(II), an enhanced adsorption capacities towards LC and Cu(II) were observed, indicating the existence of promotion in selective adsorption ability in the case of coexistence of LC and Cu(II). Besides, test of reusability suggested that the M-IIPs could be repeatedly used without any significant loss in binding capacity. Overall, this work not only provided new insights into the fabrication of porous imprinted composites with huge specific surface area and binary function, but also highlighted their application for selective and simultaneous removal of LC and Cu(II).