Synthesis of Multisegmented Degradable Polymers by Atom Transfer Radical Cross-Coupling

Developing an Electrochemically Reversible Switch for Modulating the Optical Signal of Gold Nanoparticles

Gold nanoparticles (AuNPs) possess remarkable optical properties and electrical conductivity, making them highly relevant in various fields such as medical diagnoses, biological imaging, and electronic sensors. However, the existing methods for modulating the optical properties of AuNPs are often under limitations such as a high cost, the complexity of detection, a narrow range of application settings, and irreversibility. In this study, we propose a novel approach to address these challenges by constructing a reversible electrochemical switch. The switch (ITO-OMAD) involves covalently linking nitroxide radicals and AuNPs (AuNPs-NO•), followed by tethering this nanocomposite to a siloxane-derived indium tin oxide (ITO) electrode. By simply electrochemically oxidizing/reducing the nitroxide units, one is able to reversibly modulate the optical properties of AuNPs at will. The surface morphology and structure of the as-prepared ITO-OMAD electrode were characterized through scanning electron microscopy (SEM) and cyclic voltammetry (CV). SEM imaging confirmed the successful anchoring of AuNPs on the ITO electrode. Electrochemical tests performed in the three-electrode system demonstrated that the local surface plasmon resonance (LSPR) of AuNPs can be reversibly regulated by alternatively imposing ± 0.5V (vs. Ag/AgCl) to the modified electrode. The development of this electrochemical switch presents a novel approach to effectively control the optical properties of AuNPs. The further exploration and utilization of this reversible electrochemical switch could significantly enhance the versatility and practicality of AuNPs in numerous applications.

Thermally Degradable Poly(n-butyl acrylate) Model Networks Prepared by PhotoATRP and Radical Trap-Assisted Atom Transfer Radical Coupling

Model poly(n-butyl acrylate) (PBA) networks were prepared by photoinduced atom transfer radical polymerization (photoATRP), followed by curing of polymer stars via atom transfer radical coupling (ATRC) with a nitrosobenzene radical trap. The resulting nitroxyl radical installed thermally labile alkoxyamine functional groups at the junctions of the network. The alkoxyamine crosslinks of the network were degraded back to star-like products upon exposure to temperatures above 135 °C. Characterization of the degraded products via gel permeation chromatography (GPC) confirmed the inversion of polymer topology after thermal treatment.

Tandem Living Insertion and Controlled Radical Polymerization for Polyolefin-Polyvinyl Block Copolymers

Practical synthesis of polyolefin-polyvinyl block copolymers remains a challenge for transition-metal catalyzed polymerizations. Common approaches functionalize polyolefins for post-radical polymerization via insertion methods, yet sacrifice the livingness of the olefin polymerization. This work identifies an orthogonal radical/spin coupling technique which affords tandem living insertion and controlled radical polymerization. The broad tolerance of this coupling technique has been demonstrated for diverse radical/spin traps such as 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide (TIPNO), 1-oxyl- (2,2,6,6-tetramethylpiperidine) -4-yl-α-bromoisobutyrate (TEMPO-Br), and N-tert -butyl-α-phenylnitrone (PBN). Subsequent controlled radical polymerization is demonstrated with NMP and atom transfer radical polymerization (ATRP), yielding polyolefin-polyvinyl di- and triblock copolymers ( Đ <1.3) with acrylic, vinylic and styrenic segments. These findings highlight radical trapping as an approach to expand the scope of polyolefin functionalization techniques to access polyolefin macroinitiators.

Concurrent atom transfer radical polymerization and nitroxide radical coupling relay polymerization

Simultaneous atom transfer radical polymerization (ATRP) and nitroxide radical coupling (NRC) seems impossible because the presence of nitroxide radicals would quench the radical polymerization immediately. However, by combining a nitroxide radical and an ATRP active halogen, a halogen group that can initiate one polymer chain by ATRP, into one functional reagent and adding this functional reagent to an ATRP system, concurrent ATRP-NRC relay polymerization was carried out successfully under proper reaction conditions. The key to success was the conjugate radical trapping and re-initiation took place repeatedly, resulting in polymers with inserted alkoxyamine linkages. This novel relay polymerization method provides numerous possibilities for macromolecular architecture/functionality tailoring by using of different functional reagents.

Facile topological transformation of ABA triblock copolymers into multisite, single-chain-folding and branched multiblock copolymers via sequential click coupling and anthracene chemistry

Telechelic PtBA-b-PSt-b-PtBA copolymers were designed to achieve on-demand topological transformation into multisite, single-chain-folding and branched multiblock copolymers via click/click-like reactions.

Synthesis of multisegmented block copolymer by Friedel–Crafts hydroxyalkylation polymerization

Friedel–Crafts (FC) polycondensation of 1,4-dimethoxybenzene with 4-substituted benzaldehyde species was used to prepare telechelic oligomers and high-molar-mass multisegmented block copolymers.

Biodegradable Polymeric Architectures via Reversible Deactivation Radical Polymerizations

Reversible deactivation radical polymerizations (RDRPs) have proven to be the convenient tools for the preparation of polymeric architectures and nanostructured materials. When biodegradability is conferred to these materials, many biomedical applications can be envisioned. In this review, we discuss the synthesis and applications of biodegradable polymeric architectures using different RDRPs. These biodegradable polymeric structures can be designed as well-defined star-shaped, cross-linked or hyperbranched via smartly designing the chain transfer agents and/or post-polymerization modifications. These polymers can also be exploited to fabricate micelles, vesicles and capsules via either self-assembly or cross-linking methodologies. Nanogels and hydrogels can also be prepared via RDRPs and their applications in biomedical science are also discussed. In addition to the synthetic polymers, varied natural precursors such as cellulose and biomolecules can also be employed to prepare biodegradable polymeric architectures.

Inducing an Order-Order Morphological Transition via Chemical Degradation of Amphiphilic Diblock Copolymer Nano-Objects

The disulfide-based cyclic monomer, 3-methylidene-1,9-dioxa-5,12,13-trithiacyclopentadecane-2,8-dione (MTC), is statistically copolymerized with 2-hydroxypropyl methacrylate to form a range of diblock copolymer nano-objects via reversible addition–fragmentation chain transfer (RAFT) polymerization. Poly(glycerol monomethacrylate) (PGMA) is employed as the hydrophilic stabilizer block in this aqueous polymerization-induced self-assembly (PISA) formulation, which affords pure spheres, worms or vesicles depending on the target degree of polymerization for the core-forming block. When relatively low levels (<1 mol %) of MTC are incorporated, high monomer conversions (>99%) are achieved and high blocking efficiencies are observed, as judged by ¹H NMR spectroscopy and gel permeation chromatography (GPC), respectively. However, the side reactions that are known to occur when cyclic allylic sulfides such as MTC are statistically copolymerized with methacrylic comonomers lead to relatively broad molecular weight distributions. Nevertheless, the worm-like nanoparticles obtained via PISA can be successfully transformed into spherical nanoparticles by addition of excess tris(2-carboxyethyl)phosphine (TCEP) at pH 8–9. Surprisingly, DLS and TEM studies indicate that the time scale needed for this order–order transition is significantly longer than that required for cleavage of the disulfide bonds located in the worm cores indicated by GPC analysis. This reductive degradation pathway may enable the use of these chemically degradable nanoparticles in biomedical applications, such as drug delivery systems and responsive biomaterials.

Degradable vinyl polymers for biomedical applications

Vinyl polymers have been the focus of intensive research over the past few decades and are attractive materials owing to their ease of synthesis and their broad diversity of architectures, compositions and functionalities. Their carbon-carbon backbones are extremely resistant to degradation, however, and this property limits their uses. Degradable polymers are an important field of research in polymer science and have been used in a wide range of applications spanning from (nano)medicine to microelectronics and environmental protection. The development of synthetic strategies to enable complete or partial degradation of vinyl polymers is, therefore, of great importance because it will offer new opportunities for the application of these materials. This Review captures the most recent and promising approaches to the design of degradable vinyl polymers and discusses the potential of these materials for biomedical applications.

Nitroxide-coated silver nanoparticles: synthesis, surface physicochemistry and antibacterial activity

We report the synthesis of well-defined silver nanoparticles with high antibacterial activity. Nitroxides on their surface may be oxidized under the influence of ROS to oxoammonium ions which are capable of interacting with bacterial membrane.

Synthesis, characterization, micellization and application of novel multiblock copolymers with the same compositions but different linkages

Several novel multiblock copolymers, (PEO-b-PS-b-PEO-Diyne)_s, [PEO-b-PS-b-PEO-(OH)₄]_s and (PEO-b-PS-b-PEO-Acetal)_s, with the same compositions but different linkages were constructed, and their micellization and application were studied.

Synthesis of thermally cleavable multisegmented polystyrene by an atom transfer nitroxide radical polymerization (ATNRP) mechanism

Based on the common features of well-defined NRC reaction, ATRP and NMRP mechanisms, an atom transfer nitroxide radical polymerization (ATNRP) mechanism was presented, and further used to construct multisegmented PS_m embedded with multiple alkoxyamine linkages.

Synthesis and characterization of amphiphilic triblock Copolymers with Identical compositions but different block sequences

The amphiphilic triblock copolymers PAA-b-PS-b-PAA and PS-b-PAA-b-PS were synthesized by a combination of an atom transfer radical polymerization mechanism and a nitroxide radical coupling reaction or copper-catalyzed azide/alkyne click chemistry.

A smart synthesis of gold/polystyrene core–shell nanohybrids using TEMPO coated nanoparticles

We propose a novel route for preparation of core–shell nanostructures based on the macroradicals coupling with nitroxides attached to the nanoparticle surface.

Nitroxides: applications in synthesis and in polymer chemistry

This Review describes the application of nitroxides to synthesis and polymer chemistry. The synthesis and physical properties of nitroxides are discussed first. The largest section focuses on their application as stoichiometric and catalytic oxidants in organic synthesis. The oxidation of alcohols and carbanions, as well as oxidative C-C bond-forming reactions are presented along with other typical oxidative transformations. A section is also dedicated to the extensive use of nitroxides as trapping reagents for C-centered radicals in radical chemistry. Alkoxyamines derived from nitroxides are shown to be highly useful precursors of C-centered radicals in synthesis and also in polymer chemistry. The last section discusses the basics of nitroxide-mediated radical polymerization (NMP) and also highlights new developments in the synthesis of complex polymer architectures.