Electro-selective interconversion of living cationic and radical polymerizations

Electrochemically Generated Carbocations in Organic Synthesis

This Minireview examines a selection of case studies that showcase distinctive and enabling electrochemical approaches that have allowed for the generation and reaction of carbocation intermediates under mild conditions. Particular emphasis is placed on the progress that has been made in this area of organic synthesis and polymer chemistry over the past decade.

Recent Developments on Cationic Polymerization of Vinyl Ethers

In recent times, the evolution of cationic polymerization has taken a multidirectional approach, with the development of cationic reversible addition-fragmentation chain transfer (RAFT) polymerization. In contrast to the conventional cationic polymerization methods, which were typically carried out under inert atmospheres and low temperatures, various novel polymerization techniques have been developed where the reactions are carried out in open air, operate at room temperature, are cost-effective, and are environmentally friendly. Besides, several external stimuli, such as heat, light, chemicals, electrical potential, etc. have been employed to activate and control the polymerization process. It also enables the combination of cationic polymerization with other polymerization methods in a single reaction vessel, eliminating the necessity for isolation and purification during intermediate steps. In addition, significant advancements have been made through various modifications in catalyst systems, resulting in polymers with an exceptionally high level of stereoregularity. This review article comprehensively analyses the recent developments in cationic polymerization, encompassing their applications and offering insights into future perspectives.

Interconvertible Living Radical and Cationic Polymerization using a Dual Photoelectrochemical Catalyst

The necessity of well-tuned reactivity for successful controlled polymer synthesis often comes with the price of limited monomer substrate scope. We demonstrate here the on-demand interconversion between living radical and cationic polymerization using two orthogonal stimuli and a dual responsive single catalyst. The dual photo- and electrochemical reactivity of 10-phenylphenothiazine catalyst provides control of the polymer's molar mass and composition by orthogonally activating the common dormant species toward two distinct chemical routes. This enables the synthesis of copolymer chains that consist of radically and cationically polymerized segments where the length of each block is controlled by the duration of the stimulus exposure. By alternating the application of photochemical and electrochemical stimuli, the on-demand incorporation of acrylates and vinyl ethers is achieved without compromising the end-group fidelity or dispersity of the formed polymer. The results provide a proof-of-concept for the ability to substantially extend substrate scope for block copolymer synthesis under mild, metal-free conditions through the use of a single, dual reactive catalyst.

Recent progress in the construction of polymers with advanced chain structures via hybrid, switchable, and cascade chain-growth polymerizations

Recent progress of hybrid, switchable, and cascade chain-growth polymerizations for the preparation of polymers with advanced chain structures with diverse compositions has been summarized.

Thiol-Ene Cationic and Radical Reactions: Cyclization, Step-Growth, and Concurrent Polymerizations for Thioacetal and Thioether Units

Thiol-ene cationic and radical reactions were conducted for 1:1 addition between a thiol and vinyl ether, and also for cyclization and step-growth polymerization between a dithiol and divinyl ether. p-Toluenesulfonic acid (PTSA) induced a cationic thiol-ene reaction to generate a thioacetal in high yield, whereas 2,2'-azobisisobutyronitrile resulted in a radical thiol-ene reaction to give a thioether, also in high yield. The cationic and radical addition reactions between a dithiol and divinyl ether with oxyethylene units yielded amorphous poly(thioacetal)s and crystalline poly(thioether)s, respectively. Under high-dilution conditions, the cationic and radical reactions resulted in 16- and 18-membered cyclic thioacetal and thioether products, respectively. Furthermore, concurrent cationic and radical step-growth polymerizations were realized using PTSA under UV irradiation to produce polymers having both thioacetal and thioether linkages in the main chain.

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.

100th Anniversary of Macromolecular Science Viewpoint: Photochemical Reaction Orthogonality in Modern Macromolecular Science

The ability to perform multiple chemical reactions independently (orthogonally) in a single reaction vessel can allow simplified reaction protocols for intricate chemical syntheses. Light is an especially advantageous external stimuli to enact such orthogonal chemical reactions due to its independence with other stimuli, instantaneous spatiotemporal control, and material penetrability. The potential to combine orthogonal chemistry and polymerization is also very appealing, as these systems may open the door for polymeric materials to find applications in emerging and high-tech fields, including biotechnology, microelectronics, sensors, energy, and others. We highlight the use of light in orthogonal polymerization protocols, particularly for living and controlled polymerization, and explore potential future directions and challenges for this technology.