Low ppm CuBr-Triggered Atom Transfer Radical Polymerization under Mild Conditions

CuBr-mediated surface-initiated controlled radical polymerization in air

Herein, we present a straightforward CuBr-mediated surface-initiated controlled radical polymerization (SI-CRP) method for fabricating polymer brushes using microliter volumes of reaction solution in air and at room temperature. The key advantage of this method is its ability to rapidly grow polymer brushes with oxygen tolerance, driven by the controlled disproportionation of CuI into CuII and Cu0 by CuBr and ligand. We demonstrate the successful preparation of homo-, block, patterned, and wafer-scale polymer brushes. Additionally, the catalyst in CuBr-mediated SI-CRP is reusable, long-lasting, and compatible with various monomers. This work broadens the potential of CuBr for polymer brush growth, making it accessible to both experts and non-experts.

Versatile Light-Mediated Synthesis of Degradable Bottlebrush Polymers Using α-Lipoic Acid

Bottlebrush polymers have a variety of useful properties including a high entanglement molecular weight, low Young's modulus, and rapid kinetics for self-assembly. However, the translation of bottlebrushes to real-world applications is limited by complex, multi-step synthetic pathways and polymerization reactions that rely on air-sensitive catalysts. Additionally, most bottlebrushes are non-degradable. Herein, we report an inexpensive, versatile, and simple approach to synthesize degradable bottlebrush polymers under mild reaction conditions. Our approach relies on the "grafting-through" polymerization of α-lipoic acid (LA)-functionalized macromonomers. These macromonomers can be polymerized under mild, catalyst-free conditions, and due to reversibility of the disulfide bond in LA, the resulting bottlebrush polymers can be depolymerized by cleaving disulfide backbone bonds. Bottlebrushes with various side-chain chemistries can be prepared through the atom transfer radical polymerization (ATRP) of LA-functionalized macromonomers, and the backbone length is governed by the macromonomer molecular weight and solvent polarity. We also demonstrate that LA-functionalized macromonomers can be copolymerized with acrylates to form degradable bottlebrush networks. This work demonstrates the preparation of degradable bottlebrush polymers with a variety of side-chain chemistries and provides insight into the light-mediated grafting-through polymerization of dithiolane-functionalized macromonomers.

PEGA-BA@Ce6@PFCE Micelles as Oxygen Nanoshuttles for Tumor Hypoxia Relief and Enhanced Photodynamic Therapy

Tumor hypoxia, which is mainly caused by the inefficient microvascular systems induced by rapid tumor growth, is a common characteristic of most solid tumors and has been found to hinder treatment outcomes for many types of cancer therapeutics. In this study, an amphiphilic block copolymer, poly (ethylene glycol) methyl ether acrylate-block-n-butyl acrylate (PEGA-BA), was prepared via the ATRP method and self-assembled into core-shell micelles as nano radiosensitizers. These micelles encapsulated a photosensitizer, Chlorin e6 (Ce6), and demonstrated well-defined morphology, a uniform size distribution, and high oxygen loading capacity. Cell experiments showed that PEGA-BA@Ce6@PFCE micelles could effectively enter cells. Further in vitro anticancer studies demonstrated that the PEGA-BA@Ce6@PFCE micelles significantly suppressed the tumor cell survival rate when exposed to a laser.

Visible Light-ATRP Driven by Tris(2-Pyridylmethyl)Amine (TPMA) Impurities in the Open Air

Atom transfer radical polymerization (ATRP) of oligo(ethylene oxide) monomethyl ether methacrylate (OEOMA500 ) in water is enabled using CuBr2 with tris(2-pyridylmethyl)amine (TPMA) as a ligand under blue or green-light irradiation without requiring any additional reagent, such as a photo-reductant, or the need for prior deoxygenation. Polymers with low dispersity (Đ = 1.18-1.25) are synthesized at high conversion (>95%) using TPMA from three different suppliers, while no polymerization occurred with TPMA is synthesized and purified in the laboratory. Based on spectroscopic studies, it is proposed that TPMA impurities (i.e., imine and nitrone dipyridine), which absorb blue and green light, can act as photosensitive co-catalyst(s) in a light region where neither pure TPMA nor [(TPMA)CuBr]+ absorbs light.

Oxygen-Enhanced Atom Transfer Radical Polymerization through the Formation of a Copper Superoxido Complex

In controlled radical polymerization, oxygen is typically regarded as an undesirable component resulting in terminated polymer chains, deactivated catalysts, and subsequent cessation of the polymerization. Here, we report an unusual atom transfer radical polymerization whereby oxygen favors the polymerization by triggering the in situ transformation of CuBr/L to reactive superoxido species at room temperature. Through a superoxido ARGET-ATRP mechanism, an order of magnitude faster polymerization rate and a rapid and complete initiator consumption can be achieved as opposed to when unoxidized CuBr/L was instead employed. Very high end-group fidelity has been demonstrated by mass-spectrometry and one-pot synthesis of block and multiblock copolymers while pushing the reactions to reach near-quantitative conversions in all steps. A high molecular weight polymer could also be targeted (DP_n = 6400) without compromising the control over the molar mass distributions (Đ < 1.20), even at an extremely low copper concentration (4.5 ppm). The versatility of the technique was demonstrated by the polymerization of various monomers in a controlled fashion. Notably, the efficiency of our methodology is unaffected by the purity of the starting CuBr, and even a brown highly-oxidized 15-year-old CuBr reagent enabled a rapid and controlled polymerization with a final dispersity of 1.07, thus not only reducing associated costs but also omitting the need for rigorous catalyst purification prior to polymerization.

Cu(0)-RDRP of acrylates using an alkyl iodide initiator

In the vast majority of atom transfer radical polymerizations, alkyl bromides or alkyl chlorides are commonly employed as initiators. Herein, alkyl iodides are demonstrated as ATRP initiators.

Bioenhanced Rapid Redox Initiation for RAFT Polymerization in the Air

A well-controlled bioenhanced reversible addition-fragmentation chain transfer (RAFT) in the presence of air is carried out by using glucose oxidase (GOx), glucose, ascorbic acid (Asc acid), and ppm level of hemin. The catalytic concentration of hemin is employed to enhance hydrogen peroxide (H₂ O₂ )/Asc acid redox initiation, achieving rapid RAFT polymerization. Narrow molecular weight distributions and high monomer conversion (Ð as low as 1.09 at >95% conversion) are achieved within tens of minutes. Several kinds of monomers are used to verify the universal implication of the presented method. The influences of the pH and feed ratio of each component on the polymerization rate are assessed. Besides, a polymerization rate regulation is realized by managing Asc acid addition. This work significantly increases the rate of redox-initiated GOx-deoxygen RAFT polymerization by using simple and green reactants, facilitating the application of RAFT polymerization in areas such as biomedical applications.

Tuning dispersity of linear polymers and polymeric brushes grown from nanoparticles by atom transfer radical polymerization

Molecular weight distribution imposes considerable influence on the properties of polymers, making it an important parameter, impacting morphology and structural behavior of polymeric materials.