Metal-free Atom Transfer Radical Polymerization Research Articles

Photoinduced Metal-Free Atom Transfer Radical Polymerization for the Modification of Cellulose with Poly(N-isopropylacrylamide) to Create Thermo-Responsive Injectable Hydrogels.

Photoinduced metal-free ATRP has been successfully applied to fabricate thermo-responsive cellulose graft copolymer (PNIPAM-g-Cell) using 2-bromoisobuturyl bromide-modified cellulose as the macroinitiator. The polymerization of N-isopropylacrylamide (NIPAM) from cellulose was efficiently activated and deactivated with UV irradiation in the presence of an organic-based photo-redox catalyst. Both FTIR and 13C NMR analysis confirmed the structural similarity between the obtained PNIPAM-g-Cell and that synthesized via traditional ATRP methods. When the concentration of the PNIPAM-g-Cell is over 5% in water, it forms an injectable thermos-responsive hydrogel composed of micelles at 37 °C. Since organic photocatalysis is a metal-free ATRP, it overcomes the challenge of transition-metal catalysts remaining in polymer products, making this cellulose-based graft copolymer suitable for biomedical applications. In vitro release studies demonstrated that the hydrogel can continuously release DOX for up to 10 days, and its cytotoxicity indicates that it is highly biocompatible. Based on these findings, this cellulose-based injectable, thermo-responsive drug-loaded hydrogel is suitable for intelligent drug delivery systems.

Metal-free ATRP with oligopyrene as a photocatalyst under LED irradiation

A metal-free approach to visible-light LED-induced atom transfer radical polymerization (ATRP) using oligopyrene as a photocatalyst is reported. The method facilitates the polymerization of various vinyl monomers, yielding polymers with molecular weight distribution as low as 1.32 and controlled chain-end functionality. Light on/off experiments demonstrate the light-dependent nature of the polymerization, confirming the effectiveness of the oligopyrene/alkyl halide system. The presented strategy paves the way for future advancements in polymer science, offering a metal-free alternative for controlled polymerization under visible light irradiation.

A hydrophilic near dissolved organic matter microfiltration (NDOM MF) membrane prepared using multifunctional porogen synthesized via metal-free atom transfer radical polymerization for highly efficient microplastic removal

Microplastic (MP) pollution has emerged as a global concern. One of the practical alternatives is a microfiltration (MF) process using MF membranes with a high MP removal rate and high water permeability simultaneously. In this study, we developed a highly permeable PVC-based MF membrane capable of effectively separating MP by using amphiphilic PVC, which can serve as a pore-forming agent during phase separation and as a hydrophilic modifier after solidification. We developed a new organic photocatalyst under UV light to synthesize amphiphilic PVC via metal-free atom transfer radical polymerization. With 3 wt% amphiphilic PVC, the mean pore size increased to 0.86 µm, which was 3 times larger than the control PVC membrane (0.25 µm). Furthermore, the modified PVC (m-PVC) membrane reduced the contact angle of the membrane from 80.6° to 58.3°, indicating a significant improvement in the hydrophilicity of the membrane. The larger pores and increased hydrophilic properties made the m-PVC membrane 15 times more permeable than the control, while still maintaining a removal rate of approximately 99.9 % in a water filtration test with a 1 µm bead solution. The modified PVC membrane also operated consistently under varying pH conditions. Lastly, the m-PVC membrane exhibited a 12 times lower transmembrane pressure than the control during the constant flux filtration test, resulting in a 5 times lower specific filtration energy despite a 2 times longer filtration time. We hope this study could contribute to creating a new trend in MP removal utilizing a highly porous MF membrane, which is cut out for highly efficient removal of particulate pollutants and high water permeability simultaneously.

Fabrication of well-defined lignin-derived elastomers by atom transfer radical polymerization and Diels-Alder reaction towards sustainable, super-tough and high temperature-resistant hot-melt adhesives

Hot-melt adhesives synthesized from sustainable resource have attracted increasing attention in fields of home decoration, handicraft production, automotive industries, etc., due to their free of volatile organic compounds (VOCs) and environmentally friendly advantages. However, it is still challenging to fabricate super-tough and heat-resistant hot-melt adhesives with utilization of the inherited properties of sustainable resource as feedstock. Herein, a combination of photoinduced metal-free atom transfer radical polymerization (ATRP) and Diels-Alder (DA) reaction was applied to prepare lignin-derived elastomers for super-tough and high temperature-resistant hot-melt adhesives. Firstly, photoinduced metal-free ATRP of lauryl methacrylate (LMA) derived from fatty acids and furfuryl methacrylate (FMA) derived from furfural, were employed to fabricate sustainable well-defined multi-arm lignin-graft copolymers bearing furfuryl groups with the aid of lignin based macro-initiator (L-Br). The photoinduced metal-free ATRP in this work could be activated and deactivated by an “ON–OFF” ultraviolet (UV) light switch, and successfully achieved the precise control over the molecular weight and composition of lignin-graft copolymers. Then, Diels-Alder (DA) reaction was applied to functionalize the lignin-graft copolymers with dynamic crosslinked network and obtain the lignin-derived elastomers. Benefiting from the multi-arm structure and the dynamic crosslinked network, these lignin-derived elastomers exhibited favorable mechanical property, thermal stability, shape memory, self-healing and recycled properties. In addition, the lignin-derived elastomers could be used as hot-melt adhesives and their lap shear strengths could reach 5.95 MPa, while being bonded with aluminum plates. Moreover, the steel plate bonded with lignin-derived elastomers could remain stable even at 100 °C. We believe that this work will offer a new approach for designing lignin-derived elastomers towards sustainable, strong, super-tough and high-temperature-resistant hot-melt adhesives.

Preparation and properties of UiO-66 based hybrid materials via surface initiated metal-free ATRP

A metal-organic framework (MOFs) material UiO-66-Br was synthesized via hydrothermal method, and the surface initiated metal-free atom transfer radical polymerization (SI-metal-free ATRP) of methyl methacrylate (MMA) and Eu complex were initiated on UiO-66-Br surface with UiO-66-Br as initiator and 10-phenylphenthiazine (PTH) as catalyst, and UiO-66 based hybrid materials (UiO-66-g-PMMA and UiO-66-g-PMMA-co-Eu complex) were obtained. The materials were characterized by fourier infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) thermogravimetry analysis (TGA), gel permeation chromatography (GPC), scanning electron microscopy (SEM) and so on. The results showed that the MOFs material UiO-66-Br with octahedral crystal structure was successfully synthesized, the PMMA and Eu complex chains were successfully grafted from the surface of the UiO-66-Br, the polymer grafting rate of UiO-66-g-PMMA reached 3.01 %, and the Eu content of UiO-66-g-PMMA-co-Eu complex reached 11.81 %. Water wettability test indicated that the contact angles of the hybrid materials were 155.4° and 153.3° respectively. The oil-water separation and self-cleaning experiment confirmed that the UiO-66 based hybrid materials had good oil-water separation and self-cleaning properties.

Synthesis and Self-Assembly of Hyperbranched Multiarm Copolymer Lysozyme Conjugates Based on Light-Induced Metal-Free Atrp

In recent years, the coupling of structurally and functionally controllable polymers with biologically active protein materials to obtain polymer-protein conjugates with excellent overall properties and good biocompatibility has been important research in the field of polymers. In this study, the hyperbranched polymer hP(DEGMA-co-OEGMA) was first prepared by combining self-condensation vinyl polymerization (SCVP) with photo-induced metal-free atom transfer radical polymerization (ATRP), with 2-(2-bromo-2-methylpropanoyloxy) ethyl methacrylate (BMA) as inimer, and Di (ethylene glycol) methyl ether methacrylate (DEGMA) and (oligoethylene glycol) methacrylate (OEGMA, Mn = 300) as the copolymer monomer. Then, hP(DEGMA-co-OEGMA) was used as a macroinitiator to continue the polymerization of a segment of pyridyl disulfide ethyl methacrylate (DSMA) monomer to obtain the hyperbranched multiarm copolymers hP(DEGMA-co-OEGMA)-star-PDSMA. Finally, the lysozyme with sulfhydryl groups was affixed to the hyperbranched multiarm copolymers by the exchange reaction between sulfhydryl groups and disulfide bonds to obtain the copolymer protein conjugates hP(DEGMA-co-OEGMA)-star-PLZ. Three hyperbranched multiarm copolymers with relatively close molecular weights but different degrees of branching were prepared, and all three conjugates could self-assemble to form nanoscale vesicle assemblies with narrow dispersion. The biological activity and secondary structure of lysozyme on the assemblies remained essentially unchanged.

Preparation of SiO2-g-PMMA hybrid materials employing different photocatalysts of metal-free ATRP and its application for oil-water separation

SiO2-g-PMMA hybrid materials was prepared by grafting the PMMA polymer chains from nano-SiO2 particles surface via metal-free atom transfer radical polymerization (metal-free ATRP). The FT-IR, XPS, SEM, BET and TGA tests proved that PMMA polymer chains was successfully grafted from the surface of nano-SiO2 particles. We discussed the catalytic effect and mechanism of four types photocatalysts in the preparation of SiO2-g-PMMA hybrid materials and chose Rhodamine B catalyst with reduction quenching to prepare SiO2-g-PMMA because its catalytic system has the highest conversion rate under the similar controllable degree. In addition, the kinetic analysis and chain extension reaction of the polymerization process were carried out, and it was found that the concentration of free radicals in the system remained constant, the molecular weight distribution of the polymer chains was narrow, and SiO2-g-PMMA-b-PS was successfully prepared, which indicated that the polymerization conformed the characteristics of “living /controllable” polymerization. Finally, SiO2-g-PMMA particles were cured on the fabric surface in the form of layers, the water droplets did not infiltrate on the modified layer, and the contact angle was 166.2°, showing excellent superhydrophobic properties. Moreover, the modified layer performed well in the self-cleaning experiment and oil-water separation experiment.

Recyclable magnetic Fe3O4 supported photocatalyst for the metal-free ATRP

Silica layer coated Fe3O4 magnetic nanoparticles (Fe3O4@SiO2) were used to support an photocatalyst rhodamine B (RB) (Fe3O4@SiO2-RB) for the metal-free atom transfer radical polymerization (metal-free ATRP) of methyl methacrylate (MMA) for easy separation and recycling of the catalysts. The metal-free ATRP of MMA was carried out under 365 nm UV light using Fe3O4@SiO2-RB as photocatalyst, and ethyl 2-bromoisobutyrate (EBIB) as initiator. The structure of Fe3O4@SiO2-RB was demonstrated by FT-IR, XPS, XRD and TG. The changes of morphology and specific surface area of Fe3O4 before and after modification were observed by SEM and BET. For the metal-free ATRP reaction, the polymerization process was controllable, the molecular weight was uniform and end of the molecular chain was active. The Fe3O4@SiO2-RB catalyst can be recycled through simple magnetic separation to catalyze polymerization in a controlled manner for three times, and the catalytic activity of the three polymerization reactions decreased slightly in turn. The implementation of this strategy demonstrates that the photoinitiated catalysts can be recovered and reused for subsequent light-induced ATRP.

PH and thermo dual-sensitive copolymers with fluorescent properties grafted mesoporous silica SBA-15 via metal-free ATRP

Well-defined pH and thermo dual-sensitive random copolymers poly(2-(diethylamino)ethyl methacrylate)–co-poly(N-isopropylacrylamide)–co-Eu complex with fluorescent properties grafted mesoporous silica SBA-15 (SBA-15-g-PDEAEMA-co-PNIPAM-co-Eu complex) was prepared by surface-initiated metal-free atom transfer radical polymerization (metal-free ATRP). The ATRP initiator 2-bromoisobutyryl bromide (BIBB) was immobilized on the SBA-15 surfaces followed by metal-free ATRP of 2-(diethylamino)ethyl methacrylate) (DEAEMA), N-isopropylacrylamide (NIPAM) and Eu complex. The hybrid material was characterized by fourier transform infrared spectroscope (FT-IR), nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscope (TEM), atomic force microscope (AFM), thermal gravimetric analysis (TGA), N2 adsorption/desorption measurements, X-ray powder diffraction (XRD), Fluorescence spectrum and Nanoparticle Size-Zeta potential analyzer. The results showed that the SBA-15-g-PDEAEMA-co-PNIPAM-co-Eu complex hybrid material has been prepared successfully. The pore size, pore volume and specific surface area of SBA-15 decreased after grafting of the copolymers, but the ordered structure of SBA-15 pore still remained. The fluorescence testing suggested that the hybrid material had good fluorescence characteristics. The pH and temperature sensitivity analysis suggested that the hybrid material dispersion was good under low temperature and acid condition because the polymer chains stretched.

Light-promoted synthesis of surface-grafted polymers bearing pyridine groups by metal-free ATRP in microliter volumes

Polymers with pendant pyridine groups (PPPGs) are pH responsive weak polyelectrolytes potentially attractive for many applications such as sensors, antibacterial coatings, and ion gating systems. Synthesis of PPPGs by classical atom transfer radical polymerization (ATRP) is very challenging due to highly probable formation of monomer/metal complexes. In response to that, we report here a facile synthetic strategy to obtain surface-grafted PPPGs that utilizes light-mediated ATRP. Metal-free surface-initiated ATRP catalyzed by 10-phenylphenothiazine is used to polymerize three isomeric monomers with methacrylate groups attached at various positions of a pyridine ring. The reactivity of the isomers is compared for selection of optimal monomer structure leading to thick brushes. The polymerizations are conducted under visible light, at ambient conditions, and using only microliter volumes of the reaction mixture that is important for reducing the complexity and costs of the process as well as limiting chemical waste. The observed linear dependency of the brush thickness vs polymerization time for poly(pyridin-3-yl methacrylate) (PP3M) grafted from indium tin oxide or silicon wafers indicated the controlled characteristics of the developed method. The obtained PP3M brush demonstrated pH responsive behavior associated with protonation of pyridine groups in acidic solution and adoption of highly stretched conformation below pKa.

Polymer grafted mesoporous SBA-15 material synthesized via metal-free ATRP as pH-sensitive drug carrier for quercetin

PH-sensitive amphiphilic poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) were grafted from mesoporous silica molecular sieve SBA-15 surface via metal-free atom transfer radical polymerization (metal-free ATRP). The amino group was introduced onto SBA-15 surface by silane coupling agent KH-550, followed by the ATRP initiator SBA-15-Br was obtained after bromoisobutyryl bromide (BIBB) immobilized onto SBA-15 surface. The PDEAEMA grafted SBA-15 (SBA-15-g-PDEAEMA) inorganic–organic hybrid materials were prepared by surface initiated metal-free ATRP using SBA-15-Br as initiator, 10-phenylphenothiazine (PTH) as photocatalyst, 2-(diethylamino)ethyl methacrylate (DEAEMA) as the monomer. Then, the anticancer drug quercetin was loaded onto SBA-15-g-PDEAEMA hybrid material (SBA-15-g-PDEAEMA-Qu) and the controlled release of quercetin was investigated. The analytical results indicated that the ATRP initiator has been successfully anchored onto the SBA-15 surface and the ordered structure of the mesoporous material has been maintained. The kinetic plots and the curve of the relationship between Mn and monomer conversion illustrates that the polymerization process has the characteristics of “living”/controllable radical polymerization. The TGA results showed that the graft rate of organics in SBA-15 channel is 24.7%. In vitro cytotoxicity evaluation and cell uptake assay results indicated that the cytotoxicity of SBA-15-g-PDEAEMA to the L929 cells had completely disappeared on the 3rd day, SBA-15-g-PDEAEMA has good biocompatibility and can be endocytosed by L929 cells. The drug release rate of SBA-15-g-PDEAEMA hybrid material loaded with quercetin (SBA-15-g-PDEAEMA-Qu) at pH = 5.5 is significantly higher than that at pH = 7.4, the SBA-15-g-PDEAEMA hybrid material can be used as carrier for controlled drug release and has potential application prospects in clinical practice.

Oxygen-tolerant photo-induced metal-free atom transfer radical polymerization

Well-defined poly (methyl methacrylate) (PMMA) was prepared by metal-free atom transfer radical polymerization (metal-free ATRP) using a commercially available inexpensive organic dye fluorescein (FL) as a photocatalyst, and amines as electron donors without degassing of the polymerization mixture. The effect of the molar ratio of the electron donor to FL on the kinetic and induction period during the polymerization was investigated. Moreover, the kinetics of MMA polymerization was affected by the catalyst concentration, electron donor species, and oxygen concentration in the polymerization system. Finally, the high activity of the metal-free ATRP system in the presence of a small amount of oxygen was confirmed by chain extension polymerization.

Metal-free atom transfer radical polymerization with ppm catalyst loading under sunlight

Organocatalytic atom transfer radical polymerization (O-ATRP) is recently emerging as an appealing method for the synthesis of metal-free polymer materials with well-defined microstructures and architectures. However, the development of highly effective catalysts that can be employed at a practical low loading are still a challenging task. Herein, we introduce a catalyst design logic based on heteroatom-doping of polycyclic arenes, which leads to the discovery of oxygen-doped anthanthrene (ODA) as highly effective organic photoredox catalysts for O-ATRP. In comparison with known organocatalysts, ODAs feature strong visible-light absorption together with high molar extinction coefficient (ε455nm up to 23,950 M–1 cm–1), which allow for the establishment of a controlled polymerization under sunlight at low ppm levels of catalyst loading.

Development of Environmentally Friendly Atom Transfer Radical Polymerization.

Atom transfer radical polymerization (ATRP) is one of the most successful techniques for the preparation of well-defined polymers with controllable molecular weights, narrow molecular weight distributions, specific macromolecular architectures, and precisely designed functionalities. ATRP usually involves transition-metal complex as catalyst. As the most commonly used copper complex catalyst is usually biologically toxic and environmentally unsafe, considerable interest has been focused on iron complex, enzyme, and metal-free catalysts owing to their low toxicity, inexpensive cost, commercial availability and environmental friendliness. This review aims to provide a comprehensive understanding of iron catalyst used in normal, reverse, AGET, ICAR, GAMA, and SARA ATRP, enzyme as well as metal-free catalyst mediated ATRP in the point of view of catalytic activity, initiation efficiency, and polymerization controllability. The principle of ATRP and the development of iron ligand are briefly discussed. The recent development of enzyme-mediated ATRP, the latest research progress on metal-free ATRP, and the application of metal-free ATRP in interdisciplinary areas are highlighted in sections. The prospects and challenges of these three ATRP techniques are also described in the review.

Controllable surface-initiated metal-free atom transfer radical polymerization of methyl methacrylate on mesoporous SBA-15 via reductive quenching

The surface-initiated metal-free atom transfer radical polymerization (ATRP) solution polymerization of methyl methacrylate was carried out for the first time on the basis of the reductive quenching mechanism. In this study, the 2-bromoisobutyryl bromide (BiBB) was anchored on the surface of self-synthesized rod-like mesoporous material SBA-15 as the initiator, with the commercially available organic dye fluorescein (FL) as photocatalyst and triethylamine (TEA) as electron donor under the irradiation of blue lamp. The obtained composites and polymers were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, N2 adsorption/desorption measurements, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and gel permeation chromatography. The results demonstrated that the ordered mesoporous structure of SBA-15 was not disrupted after the polymerization. With an increase in illumination time, the grafting amount and the number average molecular weight of poly(methyl methacrylate) (PMMA) on the surface of SBA-15 linearly increased, and the molecular weight distribution (Đ) widened. PMMA with a relatively narrow Đ value was obtained after polymerization for 10 h (1.47). The increase in the grafting amount and molecular weight after chain extension confirmed the chain end functionality of PMMA grafted on SBA-15.

Polymers for the Future

Laura Hartmann Mara Staffilani Miriam M. Unterlass It was in 1920 when Hermann Staudinger proposed that compounds such as cellulose or proteins were long chains composed of short repeating units, in his seminal paper “Über Polimerisation” (“On Polymerization”).[1] Since this discovery 100 years ago, polymers have had a tremendous impact on our society. Their broad success in consumer products, in agriculture, in medicine, as packaging materials, as membranes, in construction and building materials and many more areas is due to their large versatility and broad range of properties. Nevertheless, today we also face the challenges of polymers when it comes to their impact on our environment and the goal for a more and more sustainable living. Thus celebrating the 100th anniversary of polymer science is a great opportunity for Macromolecular Chemistry and Physics to initiate editorial activities aimed at highlighting the role of polymers in our society and how they may help tackling societal challenges. In a series of articles collected under the title Polymers for the Future, scientists from academia and industry were invited to provide their views on opportunities offered by advanced polymer systems in technology, biomedicine, and for a sustainable economy. The different articles nicely show both, the importance but also the diversity of Polymers for the Future. One crucial topic surely is and will remain the subject of sustainable polymers addressing societal awareness for the environment. The stability of polymers against environmental factors, chemicals, microorganisms, and hydrolysis has challenged society with the accumulation of plastic waste and its management worldwide. In her Trend article, Seema Agarwal addresses the environmental acceptability of biodegradable polymers and the opportunities and challenges they offer to solve the problem of microplastics and their impact on the environment.[2] For a sustainable economy, scientist at academia and industry need to develop green synthetic methods. Haifeng Gao and co-authors show an elegant synthetic approach for the synthesis of hyperbranched polymers using metal-free atom transfer radical polymerization (ATRP) in microemulsions. The method allows for tuning the structure and molecular weight of hyperbranched polymers using confined nanospace.[3] Healthcare is a critical issue for the growing global population. One of the topics that need to be addressed in biomedical treatments is the biological targeting at a cellular level. Protein-carbohydrate recognition is essential for a variety of biological processes, including cell growth regulation, adhesion, and cancer. In their paper Gokhan Yilmaz and C. Remzi Becer envision how precision polymeric architectures designed with advanced synthetic methods may help to better understand and utilize the protein-carbohydrate recognition in developing novel treatments.[4] Polymers have much to offer to new high-tech technologies. Lithium-ion batteries are part of modern life, being present in mobile phones, tablets, computers, watches, sport accessories, electric scooters, and cars. The current challenge is to develop a next generation of batteries with improved performance, higher safety, higher sustainability, and low price. David Mecerreyes and coauthors highlight recent developments in innovative polymers and their potential role in the next-generation batteries. They show how innovative polymers are leading to new battery technologies such as metal–polymer batteries, organic batteries, polymer–air, and redox–flow batteries, which are expected to complement the current lithium-ion technologies in the future.[5 The quest for materials with suitable property for a specific application has been the subject of research for many years. Fluoropolymers present outstanding properties that make them ideal materials for applications as protective coatings, fuel cell membranes, elastomers, specific items in automotive industries, aerospace and aeronautics, and microelectronics. Bruno Améduri provides an overview of the large range of properties exhibited by fluoropolymers and their applications. Importantly, he points to key challenges that need to be addressed in a combined effort by academic and industrial researchers.[6] An industry viewpoint on polyurethanes and their future development will be the subject of an upcoming article by Volker Schädler at BASF. These and many more upcoming contributions are being collected in the virtual special collection Polymers for the Future on the Macromolecular Chemistry and Physics website at: https://onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)1521-3935.Polymers.for.the.Future We would like to take this opportunity to also announce an upcoming perspective article on the future of polymer science written jointly by the Editors and Advisory Board of Macromolecular Chemistry and Physics. We invite you to check out for new articles at the above URL. Finally, we would like to thank all the scientists who have been sharing with us their views on what the future holds for polymer science. It was an honor to work with them all and we hope that the readers will find in the articles new inspirations for their future work and our future perspectives on polymers.

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.

PH-Sensitive, Polymer Functionalized, Nonporous Silica Nanoparticles for Quercetin Controlled Release.

Some pH-sensitive, poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) grafted silica nanoparticles (SNPs) (SNPs-g-PDEAEMA) were designed and synthesized via surface initiated, metal-free, photoinduced atom transfer radical polymerization (ATRP). The structures of the polymers formed in solution were determined by 1H NMR. The modified nanoparticles were characterized by FT-IR spectroscopy, XPS, GPC, TEM and TGA. The analytical results show that α-bromoisobutyryl bromide (BIBB) (ATRP initiator) had been successfully anchored onto SNPs’ surfaces, and was followed by surface-initiated, metal-free ATRP of 2-(diethylamino)ethyl methacrylate (DEAEMA). The resultant SNPs-g-PDEAEMA were uniform spherical nanoparticles with the particles size of about 22–25 nm, and the graft density of PDEAEMA on SNPs’ surfaces obtained by TGA was 19.98 μmol/m2. Owing to the covalent grafting of pH-sensitive PDEAEMA, SNPs-g-PDEAEMA can dispersed well in acidic aqueous solution, but poorly in neutral and alkaline aqueous solutions, which is conducive to being employed as drug carriers to construct a pH-sensitive controlled drug delivery system. In vitro cytotoxicity evaluation results showed that the cytotoxicity of SNPs-g-PDEAEMA to the L929 cells had completely disappeared on the 3rd day. The loading of quercetin on SNPs-g-PDEAEMA was performed using adsorption process from ethanol solutions, and the dialysis release rate increased sharply when the pH value of phosphate-buffered saline (PBS) decreased from 7.4 to 5.5. All these results indicated that the pH-responsive microcapsules could serve as potential anti-cancer drug carriers.

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.

Visible light-mediated metal-free atom transfer radical polymerization with N-trifluoromethylphenyl phenoxazines

The metal-free atom transfer radical polymerization (ATRP) process mediated by visible light and catalyzed by new organic photocatalysts (PCs) is investigated. The new PCs, designed by diversifying N-trifluoromethylphenyl phenoxazine, are analyzed and evaluated for organocatalyzed ATRP (O-ATRP) experimentally and theoretically. Especially, 3,7-di(4-biphenyl) 4-trifluoromethylphenyl-10-phenoxazine (4) enables successful O-ATRP with good catalytic performance, to produce well-defined polymers with low dispersity (Đ) under irradiation with a CFL bulb, white LEDs, or sunlight. The structure–property–performance relationships of PCs are investigated to determine the key parameters required for a good PC for use in O-ATRP. The scope of this process is explored in terms of monomer substrates and initiators using our new PC 4. Finally, a well-defined amphiphilic block copolymer is prepared using this method to form micelles, providing a basis for future biomedical applications.