Atom Transfer Radical Polymerization (ATRP): Current Status and Future Perspectives

Inorganic Sulfites: Efficient Reducing Agents and Supplemental Activators for Atom Transfer Radical Polymerization

Inorganic sulfites such as sodium dithionite (Na₂S₂O₄), sodium metabisulfite (Na₂S₂O₅), and sodium bisulfite (NaHSO₃) have been studied as reducing agents for atom transfer radical polymerization (ATRP). They act not only as very efficient reducing agents but also as supplemental activators for SARA (supplemental activator and reducing agent) ATRP of methyl acrylate in DMSO at ambient temperature. In combination with Cu(II)Br₂/Me₆TREN, they produced poly(methyl acrylate) with controlled molecular weight, low dispersity (M_w/M_n = 1.05), and well-defined chain-end functionality. Sulfites are eco-friendly, approved by FDA as food and beverage additives, and used commercially in many industrial processes.

Modification of the surfaces of silicon wafers with temperature-responsive cross-linkable poly[oligo(ethylene oxide) methacrylate]-based star polymers

Temperature-responsive photo-cross-linkable poly[oligo(ethylene oxide) monomethyl ether methacrylate] (POEOMA)-based star polymers were synthesized by atom transfer radical polymerization (ATRP), for the modification of silicon (Si) wafer surfaces. The polymers showed a lower critical solution temperature (LCST) behavior in aqueous media. The polymers were modified with benzophenone (Bzp) functional groups that were utilized in UV-triggered (λ = 365 nm) cross-linking reactions for the preparation of polymer networks. The star polymers were deposited onto the surfaces of Si wafers by spin coating, and stable polymer films were formed by simple UV irradiation. The stability of thermoresponsive cross-linked polymer films deposited on the Si wafer was confirmed by changing their hydrophilicity by changing the temperature of the environment. In addition, the POEOMA-based star polymers could be utilized for the preparation of photolithography-patterned surfaces. The successful formation of uniform stable polymeric films indicates that Bzp-functionalized POEOMA star polymers can be used for a simple Si surface modification.

Visible Light and Sunlight Photoinduced ATRP with ppm of Cu Catalyst

Photochemically induced ATRP was performed with visible light and sunlight in the presence of parts per million (ppm) copper catalysts. Illumination of the reaction mixture yielded polymerization in case of 392 and 450 nm light but not for 631 nm light. Sunlight was also a viable source for the photoinduced ATRP. Control experiments suggest photoreduction of the Cu^II complex (ligand to metal charge transfer in the excited state), yielding a Cu^I complex, and a bromine radical that can initiate polymerization. No photoactivation of Cu^I complex was detected. This implies that the mechanism of ATRP in the presence of light is a hybrid of ICAR and ARGET ATRP. The method was also used to synthesize block copolymers and polymerizations in water.

Preparation of cationic nanogels for nucleic acid delivery

Cationic nanogels with site-selected functionality were designed for the delivery of nucleic acid payloads targeting numerous therapeutic applications. Functional cationic nanogels containing quaternized 2-(dimethylamino)ethyl methacrylate and a cross-linker with reducible disulfide moieties (qNG) were prepared by activators generated by electron transfer (AGET) atom transfer radical polymerization (ATRP) in an inverse miniemulsion. Polyplex formation between the qNG and nucleic acid exemplified by plasmid DNA (pDNA) and short interfering RNA (siRNA duplexes) were evaluated. The delivery of polyplexes was optimized for the delivery of pDNA and siRNA to the Drosophila Schneider 2 (S2) cell-line. The qNG/nucleic acid (i.e., siRNA and pDNA) polyplexes were found to be highly effective in their capabilities to deliver their respective payloads.

Synthesis of Molecular Bottlebrushes by Atom Transfer Radical Polymerization with ppm Amounts of Cu Catalyst

Molecular bottlebrushes were prepared by ICAR (initiators for continuous activator regeneration) atom transfer radical polymerization (ATRP) and supplemental activator and reducing agent (SARA) ATRP in the presence of 50 ppm Cu-based catalyst. Poly(n-butyl acrylate) (PBA) side chains were grafted from a polymethacrylate backbone resulting in well-defined molecular bottlebrushes. Imaging of individual bottlebrush macromolecules by atomic force microscopy corroborated the targeted degrees of polymerization of the backbone and side chains. Initiation efficiency was determined by cleaving the side chains to be around 50%.

Substituted Tris(2-pyridylmethyl)amine Ligands for Highly Active ATRP Catalysts

The synthesis and application of a very active catalyst for copper-catalyzed atom transfer radical polymerizations (ATRP) with tris([(4-methoxy-2,5-dimethyl)-2-pyridyl] methyl)amine (TPMA*) ligand is reported. Catalysts with TPMA* ligands are approximately 3 orders of magnitude more active than those with tris(2-pyridylmethyl)amine (TPMA). Catalyst activity was evaluated by cyclic voltammetry, stopped-flow, and ATRP kinetics. Catalysts with TPMA* ligands perform better than those with TPMA ligands, especially at low catalyst concentrations.

Preparation of polymeric nanoscale networks from cylindrical molecular bottlebrushes

The design and control of polymeric nanoscale network structures at the molecular level remains a challenging issue. Here we construct a novel type of polymeric nanoscale networks with a unique microporous nanofiber unit employing the intra/interbrush carbonyl cross-linking of polystyrene side chains for well-defined cylindrical polystyrene molecular bottlebrushes. The size of the side chains plays a vital role in the tuning of nanostructure of networks at the molecular level. We also show that the as-prepared polymeric nanoscale networks exhibit high specific adsorption capacity per unit surface area because of the synergistic effect of their unique hierarchical porous structures. Our strategy represents a new avenue for the network unit topology and provides a new application for molecular bottlebrushes in nanotechnology.

RAFT Copolymerization of Styrene/Divinylbenzene in Supercritical Carbon Dioxide

An experimental study on the kinetics of the reversible addition–fragmentation chain transfer (RAFT) dispersion copolymerization with crosslinking of styrene and divinylbenzene in supercritical carbon dioxide (scCO2) is presented. This is the first time that such a controlled polymer network synthesis is carried out in scCO2. S-Thiobenzoyl thioglycolic acid (TBTGA) and dibenzoyl peroxide were used as RAFT agent and initiator, respectively. The polymerizations were carried out in a high pressure cell with lateral sapphire windows at 80°C. The effect of RAFT agent concentration, including the case without RAFT controller, on polymerization rate, molecular weight development, gel fraction, swelling index, and particle morphology was analysed.

Living Radical Polymerization by the RAFT Process – A Third Update

This paper provides a third update to the review of reversible deactivation radical polymerization (RDRP) achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible addition-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669) and the second in December 2009 (Aust. J. Chem. 2009, 62, 1402). This review cites over 700 publications that appeared during the period mid 2009 to early 2012 covering various aspects of RAFT polymerization which include reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses, and a diverse range of applications. This period has witnessed further significant developments, particularly in the areas of novel RAFT agents, techniques for end-group transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.