Electron Transfer-reversible Addition-fragmentation Chain Transfer Research Articles

High-Throughput Synthesis of Antimicrobial Copolymers and Rapid Evaluation of Their Bioactivity

The growing trend in antimicrobial resistance is a potential threat to our society. Due to this, the development of new antimicrobial compounds is urgently required. High-throughput compositional analysis, combined with recent advances in polymerization protocols, allows for rapid production of potentially antimicrobial compounds with minimal expertise. This can provide the impetus for correlating activity with composition and functionality. In this study, we have used high-throughput photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization to test the combinations of seven different monomers using 120 different formulations against three distinct bacterial species: Gram-negative Pseudomonas aeruginosa, Gram-positive Staphylococcus aureus, and Mycobacterium smegmatis. Through variations in composition, we have demonstrated the potential of high-throughput PET-RAFT for highly reproducible products, as well as simultaneous testing of multiple variables. Resul...

PET-RAFT Polymerization Catalyzed by Small Organic Molecule under Green Light Irradiation.

Photocatalyzed polymerization using organic molecules as catalysts has attracted broad interest because of its easy operation in ambient environments and low toxicity compared with metallic catalysts. In this work, we reported that 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT) can act as an efficient photoredox catalyst for photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization under green light irradiation. Well-defined (co)polymers can be obtained using this technique without any additional additives like noble metals and electron donors or acceptors. The living characteristics of polymerization were verified by kinetic study and the narrow dispersity (Đ) of the produced polymer. Excellent chain-end fidelity was demonstrated through chain extension as well. In addition, this technique showed great potential for various RAFT agents and monomers including acrylates and acrylamides.

SI-PET-RAFT: Surface-Initiated Photoinduced Electron Transfer-Reversible Addition-Fragmentation Chain Transfer Polymerization.

In this communication, surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer polymerization (SI-PET-RAFT) is introduced. SI-PET-RAFT affords functionalization of surfaces with spatiotemporal control and provides oxygen tolerance under ambient conditions. All hallmarks of controlled radical polymerization (CRP) are met, affording well-defined polymerization kinetics, and chain end retention to allow subsequent extension of active chain ends to form block copolymers. The modularity and versatility of SI-PET-RAFT is highlighted through significant flexibility with respect to the choice of monomer, light source and wavelength, and photoredox catalyst. The ability to obtain complex patterns in the presence of air is a significant contribution to help pave the way for CRP-based surface functionalization into commercial application.

Photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of acrylonitrile in miniemulsion

Photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of acrylonitrile (AN) in miniemulsion was reported. PET-RAFT polymerization of acrylonitrile (AN) was successfully accomplished with 4-cyanopentanoic acid dithiobenzoate (CPADB) as chain transfer agent (CTA), sodium dodecyl sulfate (SDS) as emulsifier, hexadecane (HD) as co-stabilizer and TiO2 as photocatalyst at 25 °C. The linear first-order kinetic plots were observed in miniemulsion with different amounts of SDS. Excellent temporal control was demonstrated by switching between ON/OFF states multiple times, and the prepared PAN macro-CTA was used successfully to perform the chain extension experiments, indicating high retention of chain end functionality. Furthermore, the obtained PAN was amidoximated with NH2OH·HCl. The Cd2+ was extracted with amidoxime (–C(NH2)=NOH) from aqueous solutions. The maximum adsorption of 98.6% Cd2+ with 400 mg of the adsorbent was observed at pH 6.0 and an initial Cd2+concentration of 4 mmol/L.

Perylene as a visible light photoredox catalyst for photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of MMA

The organic photocatalyst, perylene, was used to mediate photoinduced electron transfer (PET) reversible addition-fragmentation chain transfer polymerization (RAFT) of methyl methhacrylate (MMA) under light irradiation in N,N-dimethylformamide (DMF) at 25°C with 4-cyanopentanoic acid dithiobenzoate (CPADB) as chain transfer agent (CTA). Kinetic studies confirmed that the polymerization obeyed the first order kinetic m'odel. The production of PMMAs with a good control of molecular weights (Mn,GPC) and narrow polymer molecular weight distribution (Mw/Mn) were obtained. It is found that well-controlled PET RAFT polymerization of MMA can be manipulated even with the amount of perylene decreasing to ppm level. No polymer was obtained in the absence of light irradiation, implying that the model of PET RAFT polymerization of MMA is an ideal light “on”-“off” switchable system. Furthermore, the speed of PET RAFT polymerization of MMA was also finely tunable by the external light irradiation intensity. The resultant PMMA macro-CTA was characterized by 1H nuclear magnetic resonance spectrum (1H NMR) and gel permeation chromatography (GPC). The accessibility of the high end group fidelity was further demonstrated by chain extension experiments.

Towards Sequence-Controlled Antimicrobial Polymers: Effect of Polymer Block Order on Antimicrobial Activity.

Synthetic polymers have shown promise in combating multidrug-resistant bacteria. However, the biological effects of sequence control in synthetic antimicrobial polymers are currently not well understood. As such, we investigate the antimicrobial effects of monomer distribution within linear high-order quasi-block copolymers consisting of aminoethyl, phenylethyl, and hydroxyethyl acrylamides made in a one-pot synthesis approach via photoinduced electron transfer-reversible addition-fragmentation chain transfer polymerisation (PET-RAFT). Through different combinations of monomer/polymer block order, antimicrobial and haemolytic activities are tuneable in a manner comparable to antimicrobial peptides.

Photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization using titanium dioxide

Photoinitiated living radical polymerization has attracted wide attention in recent years. Titanium dioxide (TiO2) is a kind of semi-conducting metal oxide which is widely used in water treatment, photovoltaics and organic synthesis. However, there is few application in living radical polymerization. In this study, photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of methyl methacrylate (MMA) using TiO2 as photoredox catalyst is successfully carried out. It offers good control over molecular weights and polydispersities (PDI). The end group fidelity of PMMA is successfully demonstrated by chain extension for the preparation of poly(methyl methacrylate)-b-poly(dimethylaminoethyl methacrylate) (PMMA-b-PDMAEMA) copolymer. Moreover, the polymerization can be controlled by switching “ON” and “OFF” the light. Open image in new window

Visible-Light-Regulated Controlled/Living Radical Polymerization in Miniemulsion.

The implementation of photopolymerization processes in aqueous dispersed systems has the potential to afford greener approaches to the preparation of polymeric materials and has motivated researchers to perform photopolymerization in emulsion. However, these previous works have employed UV irradiation to induce photodegradation of a photoinitiator in addition to specialized equipment setups, thus limiting widespread use of these approaches. In this work, we aim to remedy these drawbacks via the implementation of photoredox catalysis in the regulation of a controlled/living radical polymerization under visible light. Utilizing the photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) process, we report the miniemulsion polymerization of styrene mediated by a household grade blue LED (λmax = 460 nm, 0.73 mW/cm2). The polymerization rate can be easily manipulated by light intensity and catalyst concentration. Finally, temporal control was demonstrated via ON/OFF experiments, which shows that no significant detriment is caused by prolonged interruptions to the light exposure.

Polymerization-Induced Self-Assembly Using Visible Light Mediated Photoinduced Electron Transfer-Reversible Addition-Fragmentation Chain Transfer Polymerization.

The ruthenium-based photoredox catalyst, Ru(bpy)3Cl2, was employed to activate reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization via a photoinduced electron transfer (PET) process under visible light (λ = 460 nm, 0.7 mW/cm2). Poly(oligo(ethylene glycol) methyl ether methacrylate) was chain extended with benzyl methacrylate to afford in situ self-assembled polymeric nanoparticles with various morphologies. The effect of different intrinsic reaction parameters, such as catalyst concentration, total solids content, and cosolvent addition was investigated with respect to the formation of different nanoparticle morphologies, including spherical micelles, worm-like micelles, and vesicles. Importantly, highly pure worm-like micelles were readily isolated due to the in situ formation of highly viscous gels. Finally, "ON/OFF" control over the dispersion polymerization was demonstrated by online Fourier transform near-infrared (FTNIR) spectroscopy, allowing for temporal control over the nanoparticle morphology.

Stereo-, Temporal and Chemical Control through Photoactivation of Living Radical Polymerization: Synthesis of Block and Gradient Copolymers.

Nature has developed efficient polymerization processes, which allow the synthesis of complex macromolecules with a perfect control of tacticity as well as molecular weight, in response to a specific stimulus. In this contribution, we report the synthesis of various stereopolymers by combining a photoactivated living polymerization, named photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) with Lewis acid mediators. We initially investigated the tolerance of two different photoredox catalysts, i.e., Ir(ppy)3 and Ru(bpy)3, in the presence of a Lewis acid, i.e., Y(OTf)3 and Yb(OTf)3, to mediate the polymerization of N,N-dimethyl acrylamide (DMAA). An excellent control of tacticity as well as molecular weight and dispersity was observed when Ir(ppy)3 and Y(OTf)3 were employed in a methanol/toluene mixture, while no polymerization or poor control was observed with Ru(bpy)3. In comparison to a thermal system, a lower amount of Y(OTf)3 was required to achieve good control over the tacticity. Taking advantage of the temporal control inherent in our system, we were able to design complex macromolecular architectures, such as atactic block-isotactic and isotactic-block-atactic polymers in a one-pot polymerization approach. Furthermore, we discovered that we could modulate the degree of tacticity through a chemical stimulus, by varying [DMSO]0/[Y(OTf)3]0 ratio from 0 to 30 during the polymerization. The stereochemical control afforded by the addition of a low amount of DMSO in conjunction with the inherent temporal control enabled the synthesis of stereogradient polymer consisting of five different stereoblocks in one-pot polymerization.

Exploiting Metalloporphyrins for Selective Living Radical Polymerization Tunable over Visible Wavelengths

The use of metalloporphyrins has been gaining popularity particularly in the area of medicine concerning sensitizers for the treatment of cancer and dermatological diseases through photodynamic therapy (PDT), and advanced materials for engineering molecular antenna for harvesting solar energy. In line with the myriad functions of metalloporphyrins, we investigated their capability for photoinduced living polymerization under visible light irradiation over a broad range of wavelengths. We discovered that zinc porphyrins (i.e., zinc tetraphenylporphine (ZnTPP)) were able to selectively activate photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of trithiocarbonate compounds for the polymerization of styrene, (meth)acrylates and (meth)acrylamides under a broad range of wavelengths (from 435 to 655 nm). Interestingly, other thiocarbonylthio compounds (dithiobenzoate, dithiocarbamate and xanthate) were not effectively activated in the presence of ZnTPP. This selectivity was likely attributed to a specific interaction between ZnTPP and trithiocarbonates, suggesting novel recognition at the molecular level. This interaction between the photoredox catalyst and trithiocarbonate group confers specific properties to this polymerization, such as oxygen tolerance, enabling living radical polymerization in the presence of air and also ability to manipulate the polymerization rates (kp(app) from 1.2-2.6 × 10(-2) min(-1)) by varying the visible wavelengths.

Organo-photocatalysts for photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization

In this work, we demonstrate the use of organophotoredox catalysts under visible light to perform photoinduced electron transfer-reversible addition fragmentation chain transfer (PET-RAFT) for the polymerization of methacrylate monomers.

Combining Enzymatic Monomer Transformation with Photoinduced Electron Transfer - Reversible Addition-Fragmentation Chain Transfer for the Synthesis of Complex Multiblock Copolymers.

A novel and facile method, involving enzymatic monomer synthesis and a photocontrolled polymerization technique, has been successfully employed for the preparation of high-order multiblock copolymers. New acrylate monomers were synthesized via enzymatic transacylation between an activated monomer, i.e., 2,2,2-trifluoroethyl acrylate (TFEA), and various functional alcohols. These synthesized monomers were successfully polymerized without further purification via photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization under low energy blue LED light (4.8 W) in the presence of an iridium-based photoredox catalyst (fac-[Ir(ppy)3]). In this condition, PET-RAFT allows us to achieve high monomer conversion (∼100%) with excellent integrity of the end group (>80%). Different multiblock (co)polymers, including poly(hexyl acrylate) pentablock homopolymer, poly(methyl acylate-b-ethyl acrylate-b-n-propyl acrylate-b-n-butyl acrylate-b-n-pentyl acrylate) pentablock copolymer, and poly(3-oxobutyl acrylate-b-methyl acrylate-b-3-(trimethylsilyl)prop-2-yn-1-yl acrylate) triblock copolymer containing functional groups were rapidly prepared via sequential addition of monomers without purification steps.

SET‐RAFT of MMA mediated by ascorbic acid‐activated copper oxide

AbstractIn this work, cupric oxide (CuO) or cuprous oxide (Cu2O) was used as the catalyst for the single electron transfer‐reversible addition‐fragmentation chain transfer (SET‐RAFT) polymerization of methyl methacrylate in the presence of ascorbic acid at 25 °C. 2‐Cyanoprop‐2‐yl‐1‐dithionaphthalate (CPDN) was used as the RAFT agent. The polymerization occurred smoothly after an induction period arising from the slow activation of CuO (or Cu2O) and the “initialization” process in RAFT polymerization. The polymerizations conveyed features of “living”/controlled radical polymerizations: linear evolution of number‐average molecular weight with monomer conversion, narrow molecular weight distribution, and high retention of chain end fidelity. From the polymerization profile, it was deduced that the polymerization proceeded via a conjunct mechanism of single electron transfer‐living radical polymerization (SET‐LRP) and RAFT polymerization, wherein CPDN acting as the initiator for SET‐LRP and chain transfer agent for RAFT polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012