Reversible redox controlled acids for cationic ring-opening polymerization

Advancements in externally controlled polymerization methodologies have enabled the synthesis of novel polymeric structures and architectures, and they have been pivotal to the development of new photocontrolled lithographic and 3D printing technologies. In particular, the development of externally controlled ring-opening polymerization (ROP) methodologies is of great interest, as these methods provide access to novel biocompatible and biodegradable block polymer structures. Although ROPs mediated by photoacid generators have made significant contributions to the fields of lithography and microelectronics development, these methodologies rely upon catalysts with poor stability and thus poor temporal control. Herein, we report a class of ferrocene-derived acid catalysts whose acidity can be altered through reversible oxidation and reduction of the ferrocenyl moiety to chemically and electrochemically control the ROP of cyclic esters.

Electrochemistry for Atom Transfer Radical Polymerization

Atom Transfer Radical Polymerization (ATRP) is the most powerful and most employed technology of Controlled Radical Polymerization (CRP) to produce polymers with well-defined architecture, that is, composition, topology, and functionality. Several hundreds of papers are published every year on ATRP processes, mainly based on empiric experimental procedures. Electrochemistry powerfully entered in the field of ATRP about 10 years ago, providing important contributions both to the further development of the process and to a better understanding of its mechanism. Five main issues took advantage of electrochemistry and/or its synergism with ATRP: i) understanding the mechanism of ATRP activation; ii) determination of thermodynamic parameters; iii) determination of activation and deactivation rate constants; iv) the SARA ATRP vs SET-LRP dispute: the role of Cu⁰ ; v) electrochemically-mediated ATRP.

Role of External Field in Polymerization: Mechanism and Kinetics

The past decades have witnessed an increasing interest in developing advanced polymerization techniques subjected to external fields. Various physical modulations, such as temperature, light, electricity, magnetic field, ultrasound, and microwave irradiation, are noninvasive means, having superb but distinct abilities to regulate polymerizations in terms of process intensification and spatial and temporal controls. Gas as an emerging regulator plays a distinctive role in controlling polymerization and resembles a physical regulator in some cases. This review provides a systematic overview of seven types of external-field-regulated polymerizations, ranging from chain-growth to step-growth polymerization. A detailed account of the relevant mechanism and kinetics is provided to better understand the role of each external field in polymerization. In addition, given the crucial role of modeling and simulation in mechanisms and kinetics investigation, an overview of model construction and typical numerical methods used in this field as well as highlights of the interaction between experiment and simulation toward kinetics in the existing systems are given. At the end, limitations and future perspectives for this field are critically discussed. This state-of-the-art research progress not only provides the fundamental principles underlying external-field-regulated polymerizations but also stimulates new development of advanced polymerization methods.

Dual atom transfer radical polymerization for ultrasensitive electrochemical DNA detection

Atom transfer radical polymerization as a form of controlled/living radical polymerization is particularly attractive. In this work, dual atom transfer radical polymerization (ATRP) is reported for ultrasensitive DNA detection. Firstly, a peptide nucleic acid (PNA) modified with a thiol group was self-assembled on an electrode surface to capture target DNA (TDNA). The initiator of the first ATRP (ATRP-1), α-bromoisobutyric acid (BIBA), was linked to forming PNA/DNA heteroduplexes via coordination of Zr⁴⁺. The polymer chain formed by the monomer of ATRP-1 (2-(2-bromoisobutyryloxy) ethyl methacrylate, BIEM) was also one of initiators of the second ATRP (eATRP-2). The other initiator of eATRP-2 was additional BIBA. ATRP-1 involves activator regeneration by electron transfer (ARGET) ATRP, regulated via excess reducing agent. eATRP-2 is electrochemically mediated ATRP which can control the polymerization via an appropriate applied potential. Compared with one ATRP, more monomers of eATRP-2 modified with ferrocene are attached to electrode surface. Under optimal conditions, this dual ATRP strategy provides a low limit of detection (25 aM, ~150 molecules) with satisfactory selectivity and stability. Importantly, this strategy presents a useful prospect for the field of biomolecule detection.

Under pressure: electrochemically-mediated atom transfer radical polymerization of vinyl chloride

Electrochemically mediated ATRP (eATRP) of vinyl chloride (VC), a less activated monomer, was successfully achieved. It is the first report on eATRP of a gaseous monomer under pressure.

Electrochemical Behavior of Thiocarbonylthio Chain Transfer Agents for RAFT Polymerization

Electrochemical activation of thiocarbonylthio reversible addition-fragmentation chain transfer (RAFT) agents (S=C(Z)S-R) is explored as a potential method for initiating RAFT polymerization under mild conditions without producing initiator-derived byproducts. Herein we apply cyclic voltammetry to establish a predominant reduction mechanism, where electrochemical reduction is coupled to an irreversible first-order chemical reaction. Structure-dependent trends in cyclic voltammograms (CVs), and comparison to absorption spectra, clarify the role of R- and Z-groups in determining reduction processes. The major reduction peak moves to more cathodic potentials in the series dithiobenzoates > trithiocarbonates > heteroaromatic dithiocarbamates > xanthates ∼ N-alkyl-N-aryldithiocarbamates, due to the Z-group influence on thiocarbonyl bond reactivity. More active (electron-withdrawing, radical stabilizing) R-groups shift the reduction peak anodically, in part due to their influence on the rate of the coupled chemical reaction. Analysis of CVs across a range of scan rates revealed that kinetic control over the reduction mechanism is influenced by both the charge transfer rate and chemical reaction rate.