Organic nanoparticles with tunable size and rigidity by hyperbranching and cross-linking using microemulsion ATRP

Unlike inorganic nanoparticles, organic nanoparticles (oNPs) offer the advantage of "interior tailorability," thereby enabling the controlled variation of physicochemical characteristics and functionalities, for example, by incorporation of diverse functional small molecules. In this study, a unique inimer-based microemulsion approach is presented to realize oNPs with enhanced control of chemical and mechanical properties by deliberate variation of the degree of hyperbranching or cross-linking. The use of anionic cosurfactants led to oNPs with superior uniformity. Benefitting from the high initiator concentration from inimer and preserved chain-end functionality during atom transfer radical polymerization (ATRP), the capability of oNPs as a multifunctional macroinitiator for the subsequent surface-initiated ATRP was demonstrated. This facilitated the synthesis of densely tethered poly(methyl methacrylate) brush oNPs. Detailed analysis revealed that exceptionally high grafting densities (~1 nm-2) were attributable to multilayer surface grafting from oNPs due to the hyperbranched macromolecular architecture. The ability to control functional attributes along with elastic properties renders this "bottom-up" synthetic strategy of macroinitiator-type oNPs a unique platform for realizing functional materials with a broad spectrum of applications.

PDMAEMA from α to ω chain ends: tools for elucidating the structure of poly(2-(dimethylamino)ethyl methacrylate)

An in-depth characterization of PDMAEMA prepared by ATRP was conducted, with a focus on end group analysis. This work discusses analytical tools providing essential information about the extent of control over DMAEMA polymerization and chain extension.

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.

Progress on the development of a metal salt-assisted ionization source for the mass spectrometric analysis of polymers

The mass spectrometric analysis of polymers has been addressed as a challenging research topic due to poor ionization and complicated analysis using conventional mass spectrometry. The ionization source has demonstrated a promising future in rapid mass spectrometric analysis. Soft ionization techniques, such as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) are the most ionization sources appeared to be a powerful tools for polymer characterization when combined with MS. However, they always need metal salts to be introduced during the ionization protocol for polymers due to the crucial role played by their ions (cations and anions). The current review focuses on the progress in the development of metal ion-assisted-ionization sources for the mass spectrometric analysis of polymers. Different ionization systems are comprehensively reviewed. The application of metal ion-assisted ESI, nanoESI, PSI, and MALDI-MS for polymer sample analyses is systematically discussed. The future research trends and challenges in this cutting-edge research field are summarized. It also aims to provide the current state-of-the-art of metal salts as a platform for ionization systems for the mass spectrometric characterization of polymers and offers the current challenges and perspectives on the promising future to improve analytical performance in this field. Finally, this mini-review provides a comprehensive handbook to researchers from different research backgrounds wishing to work in this area.

Structurally nanoengineered antimicrobial peptide polymers: design, synthesis and biomedical applications

Antimicrobial resistance not only increases the contagiousness of infectious diseases but also a threat for the future as it is one of the health care concern around the globe. Conventional antibiotics are unsuccessful in combating chronic infections caused by multidrug-resistant (MDR) bacteria, therefore it is important to design and develop novel strategies to tackle this problems. Among various novel strategies, Structurally Nanoengineered Antimicrobial Peptide Polymers (SNAPPs) have been introduced in recent years to overcome this global health care issue and they are found to be more efficient in their performance. Many facile methods are adapted to synthesize complex SNAPPs with required dimensions and unique functionalities. Their unique characteristics and remarkable properties have been exploited for their immense applications in various fields including biomedicine, targeting therapies, gene delivery, bioimaging, and many more. This review article deals with its background, design, synthesis, mechanism of action, and wider applications in various fields of SNAPPs.

Polymers via Reversible Addition-Fragmentation Chain Transfer Polymerization with High Thiol End-Group Fidelity for Effective Grafting-To Gold Nanoparticles

End-group fidelity is the most important property for end-functional polymers. Compared to other controlled living polymerization methods, reversible addition-fragmentation chain transfer (RAFT) polymerization often yields polymers with a lower end-group fidelity, which greatly affects their applications. Herein, we report a staged-thermal-initiation RAFT polymerization for the synthesis of polymers with high thiol end-group fidelity and their high efficiencies for grafting to various gold nanoparticles (GNPs). We experimentally prove that the decrease of end-group fidelity with their molecular weight is caused by the gradual decomposition of the initiator rather than the degradation of chain-transfer agents. We show that the staged-thermal-initiation RAFT polymerization is more effective for synthesis of polymers with high thiol end-group fidelity. The grafting-to assays for various GNPs illustrate the positive correlation between the end-group fidelity of polymers and grafting-to efficiency. This work highlights the prospects for synthesis of high end-group fidelity polymers and their application in the preparation of nanoparticles-polymer hybrid materials.

The signal-to-noise issue in mass spectrometric analysis of polymers

Mass spectrometric approaches to polymer analysis become increasingly ineffective as average molecular weight increases. This perspective explains these fundamental limits of MS for determining molecular weight distribution of high polymers.

Can We Push Rapid Reversible Deactivation Radical Polymerizations toward Immortality?

All reversible deactivation radical polymerization (RDRP) processes require a compromise between the rate of polymerization, which requires a high radical concentration, and retention of chain end functionality, which requires a low radical concentration. Here, we demonstrate that this compromise may be partially averted where fast deactivation of the propagating radical occurs. It is shown that, contrary to the predictions of classical reaction kinetics, when the probability density functions of the termination reactions are adjusted to take into account the time needed for radical diffusion, a reduction in the extent of termination can be expected if chain deactivation is rapid. We subsequently use this framework to explain experimental results in the copper(0)-mediated polymerization of acrylamide. The main concept put forward in the paper questions the commonly held assumptions of the limitations of RDRP processes and suggests the ability for a seemingly impossible level of control of radical reactions.

ATRP of Methyl Acrylate by Continuous Feeding of Activators Giving Polymers with Predictable End-Group Fidelity

Atom transfer radical polymerization (ATRP) of methyl acrylate (MA) was carried out by continuous feeding of Cu(I) activators. Typically, the solvent, the monomer, the initiator, and the CuBr2/Me6TREN deactivator are placed in a Schlenk flask (Me6TREN: tris[2-(dimethylamino)ethyl]amine), while the CuBr/Me6TREN activator is placed in a gas-tight syringe and added to the reaction mixture at a constant addition rate by using a syringe pump. As expected, the polymerization started when Cu(I) was added and stopped when the addition was completed, and polymers with a narrow molecular weight distribution were obtained. The polymerization rate could be easily adjusted by changing the activator feeding rate. More importantly, the loss of chain end-groups could be precisely predicted since each loss of Br from the chain end resulted in the irreversible oxidation of one Cu(I) to Cu(II). The Cu(I) added to the reaction system may undergo many oxidation/reduction cycles in ATRP equilibrium, but would finally be oxidized to Cu(II) irreversibly. Thus, the loss of chain end-groups simply equals the total amount of Cu(I) added. This technique provides a neat way to synthesize functional polymers with known end-group fidelity.

Bottom-up design of model network elastomers and hydrogels from precise star polymers

Well-defined high-molecular weight star polymers based on low-T_g water-soluble polymers enable bottom-up design of model network elastomers and functional hydrogels.

Fast track access to multi-block copolymers via thiol-bromo click reaction of telechelic dibromo polymers

Multi-block copolymers offer a plethora of exciting properties, easily tuned by modulating parameters such as monomer composition, block length, block number and dispersity.

Recent Developments in the Synthesis of Biomacromolecules and their Conjugates by Single Electron Transfer-Living Radical Polymerization

Single electron transfer-living radical polymerization (SET-LRP) represents a robust and versatile tool for the synthesis of vinyl polymers with well-defined topology and chain end functionality. The crucial step in SET-LRP is the disproportionation of the Cu(I)X generated by activation with Cu(0) wire, powder, or nascent Cu(0) generated in situ into nascent, extremely reactive Cu(0) atoms and nanoparticles and Cu(II)X₂. Nascent Cu(0) activates the initiator and dormant chains via a homogeneous or heterogeneous outer-sphere single-electron transfer mechanism (SET-LRP). SET-LRP provides an ultrafast polymerization of a plethora of monomers (e.g., (meth)-acrylates, (meth)-acrylamides, styrene, and vinyl chloride) including hydrophobic and water insoluble to hydrophilic and water soluble. Some advantageous features of SET-LRP are (i) the use of Cu(0) wire or powder as readily available catalysts under mild reaction conditions, (ii) their excellent control over molecular weight evolution and distribution as well as polymer chain ends, (iii) their high functional group tolerance allowing the polymerization of commercial-grade monomers, and (iv) the limited purification required for the resulting polymers. In this Perspective, we highlight the recent advancements of SET-LRP in the synthesis of biomacromolecules and of their conjugates.

End group modification of poly(acrylates) obtained via ATRP: a user guide

The versatile and high yielding end-functionalization with a varienty of functional groups is presented for poly(acrylates) obtained by ATRP.

Star Polymers

Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

Cu(0)-mediated living radical polymerization: recent highlights and applications; a perspective

Cu(0)-mediated living radical polymerization or single electron transfer living radical polymerization (Cu(0)-mediated LRP or SET-LRP) is a versatile polymerization technique that has attracted considerable interest during the past few years for the facile preparation of advanced materials.

Discrete copper(ii)-formate complexes as catalytic precursors for photo-induced reversible deactivation polymerization

Traditional copper-mediated reversible deactivation polymerization techniques (RDRP) employ various components mixedin situ(e.g.ligand, metal salt, additional deactivation speciesetc.) in order to achieve good control over the molecular weight distributions.

Access to Multiblock Copolymers via Supramolecular Host-Guest Chemistry and Photochemical Ligation

We combine supramolecular host-guest interactions of β-cyclodextrin (CD) with light-induced Diels-Alder reactions of 2-methoxy-6-methylbenzaldehyde (photoenol, PE) for the formation of multiblock copolymers. Via the synthesis of a new bifunctional chain transfer agent (CTA) and subsequent reversible addition-fragmentation chain transfer (RAFT) polymerization, we introduce a supramolecular recognition unit (tert-butyl phenyl) and a photoactive unit (photoenol) to a polymer chain in order to obtain an α,ω-functionalized polymeric center block, having orthogonal recognition units at each chain end. Multiblock copolymers are formed via the light-induced reaction of the photoenol with a maleimide-functionalized polymer chain and the supramolecular self-assembly of the tert-butyl phenyl group with the β-CD end group of a third polymer chain. By employing the fast and efficient photoinduced Diels-Alder reaction in combination with supramolecular host-guest interactions, a novel method for macromolecular modular ligation is introduced.

Insights into relevant mechanistic aspects about the induction period of Cu0/Me6TREN-mediated reversible-deactivation radical polymerization

The induction period and subsequent autoaccelerated polymerization of a Cu⁰/Me₆TREN-catalyzed system originate from the accumulation of soluble copper species.

Aqueous SET-LRP catalyzed with “in situ” generated Cu(0) demonstrates surface mediated activation and bimolecular termination

Ultrafast, inversely temperature dependent aqueous SET-LRP with “in situ” generated Cu(0) yields quantitative chain-ends demonstrating surface mediated activation and termination.

In the (Very) Long Run We Are All Dead: Activation and Termination in SET-LRP/SARA-ATRP

The rate constants of activation and termination were determined for SET-LRP/SARA-ATRP polymerizations of methyl acrylate. Measurement of the rate of generation of CuBr₂ throughout the reaction (using data from Levere et al., Macromolecules 2012, 45, 8267-8274) allowed evaluation of the chain length dependence of the two rate constants, which were found to be 1.25(9) × 10^-4DP_n^-0.51(3) cm·s^-1 (activation) and 3.1(1) × 10⁹DP_n^-0.49(2) L·mol^-1·s^-1 (termination). Addition of the CuBr₂ deactivator at the beginning of the reaction is found to result in a higher proportion of dead chains due to rapid termination of short chains.

Synthesis and Aggregation of Double Hydrophilic Diblock Glycopolymers via Aqueous SET-LRP

A chemically unprotected mannose-containing acrylate (ManA) monomer was synthesized and polymerized by Cu(0)-mediated radical polymerization in water (SET-LRP). One-pot block copolymerization was achieved upon addition of a solution of N-isopropylacrylamide (NIPAm) or diethylene glycol ethyl ether acrylate (DEGEEA) forming thermoresponsive double hydrophilic diblock glycopolymers which revealed self-assembly properties in aqueous solution forming well-defined, sugar-decorated nanoparticles.

Self-activation and activation of Cu(0) wire for SET-LRP mediated by fluorinated alcohols

Herein we report the self-activation and activation of Cu(0) wire used to form a catalyst in single-electron transfer living radical polymerization (SET-LRP) in two fluorinated alcohols employed as solvents, 2,2,2-trifluoroethanol (TFE) and 2,2,3,3-tetrafluoropropanol (TFP).

Cu(0)-mediated polymerization of hydrophobic acrylates using high-throughput experimentation

In this paper the optimization of the Cu(0)-mediated polymerization of n-butyl acrylate and 2-methoxyethyl acrylate is reported using an automated parallel synthesizer.