Visible light-controlled living cationic polymerization of methoxystyrene

Study of high-strength, low-shrinkage dental resin composites with bifunctional polysilsesquioxane

OBJECTIVES

The aim of this study was to develop a new composite resin to solve the problem of volume shrinkage of conventional dental restorative composite resins during the curing process in order to improve their mechanical properties and reduce the risk of restoration failure.

METHODS

We synthesized the mercapto-alkenyl click chemical reaction product (MN-POSS) of acrylate-based POSS (MAP-POSS) with N-Acetylcysteine (NAC) using a bifunctional polysilsesquioxane modification technique and improved its dispersion in the resin matrix by physicochemical methods. In addition, methacrylate-based epoxy POSS (ME-POSS) was further synthesized and used to modify acrylate dental resins to form a free radical-cation hybrid light-curing system.

RESULTS

The results showed that the composites modified with MN-POSS significantly improved mechanical strength, while the application of ME-POSS effectively reduced polymerization shrinkage, improved the water absorption and dissolution properties of the materials, and enhanced mechanical properties and hardness. This study provides new ideas and material solutions to improve the performance of dental restorative materials.

SIGNIFICANCE

Both of these improved solutions demonstrate the potential of bifunctional POSS as a modified filler, providing new ideas and methods for the design of future dental restorative materials.

Triarylmethyl Cations as Photocatalysts for Radical-Mediated Cycloaddition Reactions

We have developed a novel photocatalytic system using readily available triarylmethyl cations for radical-mediated (4 + 2) and (2 + 2) cycloaddition reactions. A variety of substituted triarylmethyl cations were investigated, and the optimal catalyst exhibited high efficiency and broad substrate scope, affording the desired cycloadducts in good to excellent yields with high regio- and diastereoselectivities. Furthermore, the catalyst could be immobilized on a polymer support and reused multiple times without a significant loss of activity.

Recycling Polyester and Polycarbonate Plastics with Carbocation Lewis Acidic Organocatalysts

The effective management of plastic waste is critical for environmental sustainability. This work explores the use of carbocation catalysts for the recycling of common polyesters and polycarbonates through alcoholysis. We demonstrate complete depolymerization of end-of-life materials and investigate the relationship between the catalytic reactivity and the structural features of the carbocation compounds, including the cations and their counteranions. Carbocations function as Lewis acids, facilitating the interaction with carbonyls in polymer chains. Moreover, our approach enables the hierarchical degradation of the polyester blends. This research not only elucidates the catalytic role of carbocations in the alcoholysis of these polymers, but also establishes a metal-free process for the efficient recycling of waste plastics.

Enabling controllable time-dependent phosphorescence in carbonized polymer dots based on chromophore excited triplet energy level modulation by ionic bonding

Time-dependent phosphorescence color (TDPC) materials are highly attractive for realizing multitiered dynamic information encryption and anti-counterfeiting. It's extremely challenging to modulate puzzle of multiple luminescence species and understand the intrinsic mechanism. Herein, we demonstrate a novel and synthesize-friendly strategy to develop a high contrast TDPC carbonized polymer dots (CPDs) with adjustable lifetime and quantum yields. The ionic bonding is introduced in self-protected CPDs to effectively tune the excited triplet energy level of chromophores, and promote the stable existence of L-aspartic (AA) with green phosphorescence at 545 nm, and alkali metal aspartates (AA-M) with red phosphorescence at 665 nm. The precise regulation for TDPC lifetime can be achieved based on heavy atom effort and crosslink-enhanced emission (CEE) effect. And, the efficient radiative energy transfer could be proven as an intrinsic mechanism for better understanding the TDPC materials. These results further expand on the fundamental principle to design high-quality TDPC materials with more flexible regulation for luminescence properties, providing a major step forward in broadening the scope of smart phosphorescence applications.

Universal Copolymerization of Crosslinked Polyether Electrolytes for All-Solid-State Lithium-Metal Batteries

Solid polymer electrolytes (SPEs) are pivotal in advancing the practical implementation of all-solid-state batteries. Poly(1,3-dioxane) (PDOL)-based electrolytes have attracted significant attention due to the pseudo-high conductivity achieved through sophisticated in situ polymerization methods; however, such PDOL-based electrolytes present challenges of crystallization over time and monomers residual during processing. In this study, integrating LiTFSI and LiDFOB as a universal copolymerization strategy for developing high-performance PDOL electrolytes with a wide range of epoxy crosslinkers is proposed. It is discovered that this approach leverages the protective effects of TFSI anions on the boron active center and catalyzes polymer chain growth via crosslinking. The homogenously crosslinked (benzene-centered) PDOL electrolyte exhibits remarkable thermo-mechanical stability (up to 100 °C), high ion migration number (tLi+ = 0.42), a wide electrochemical window (≈5.0 V vs Li+/Li), and high ionic conductivity (4.5×10-4 S cm-1). Notably, the crosslinked PDOL electrolyte is in the all-solid-state with minimal monomer/oligomer residual, exhibiting no crystallization during relaxation, delivering a robust performance in all-solid-state lithium metal batteries.

Protein-polymer bioconjugation, immobilization, and encapsulation: a comparative review towards applicability, functionality, activity, and stability

Polymer-based biomaterials have received a lot of attention due to their biomedical, agricultural, and industrial potential. Soluble protein-polymer bioconjugates, immobilized proteins, and encapsulated proteins have been shown to tune enzymatic activity, improved pharmacokinetic ability, increased chemical and thermal stability, stimuli responsiveness, and introduced protein recovery. Controlled polymerization techniques, increased protein-polymer attachment techniques, improved polymer surface grafting techniques, controlled polymersome self-assembly, and sophisticated characterization methods have been utilized for the development of well-defined polymer-based biomaterials. In this review we aim to provide a brief account of the field, compare these methods for engineering biomaterials, provide future directions for the field, and highlight impacts of these forms of bioconjugation.

Asymmetric Ion-Pairing Photoredox Catalysis for Stereoselective Cationic Polymerization under Light Control

By virtue of noninvasive regulations by light, photocontrolled polymerizations have attracted considerable attention for the precision synthesis of macromolecules. However, a cationic polymerization with simultaneous photocontrol and tacticity-regulation remains elusive so far. Herein, we introduce an asymmetric ion-pairing photoredox catalysis strategy that allows for the development of a stereoselective cationic polymerization with concurrent light regulation for the first time. By employing an ion pair catalyst (PC+/*A-) consisting of a photoredox active cation (PC+) and a sterically confined chiral anion (*A-) to deliver the stereochemical control, the cationic polymerization of vinyl ethers can be achieved with photocontrol and high isotactic selectivity (up to 91% m) at a remarkable low catalyst loading (50 ppm).

Visible Light-Regulated Ring-Opening Polymerization of Lactones by Employing Indigo as a Photoacid Catalyst

The development of visible light-regulated polymerizations for precision synthesis of polymers has drawn considerable attention in the past years. In this study, an ancient dye, indigo, is successfully identified as a new and efficient photoacid catalyst, which can readily promote the ring-opening polymerization of lactones under visible light irradiation in a well-controlled manner, affording the desired polyester products with predictable molecular weights and narrow dispersity. The enhanced acidity of indigos by excitation is crucial to the H-bonding activation of the lactone monomers. Chain extension and block copolymer synthesis are also demonstrated with this method.

Zinc-Mediated Living Cationic Polymerization

Here, we present a facile and robust method for living cationic polymerization using zinc wire as a catalyst precursor. Well-defined poly(vinyl ether)s with various molecular weights and narrow molecular weight distributions (Đ < 1.10) can be achieved at room temperature. Excellent living characteristics were observed in kinetic and chain extension experiments. Mechanistic investigations revealed that the polymerization was catalyzed by the in situ generation of trace zinc ions, which is the key to polymerization under mild conditions. The utilization of zinc wire offers several advantages, including reusability, easy separation and low metal residue. Furthermore, we extended the application of this method in continuous flow polymerization, opening up a promising avenue for scalable and efficient industrial production under mild conditions.

Visualizing Chain Growth of Polytelluoxane via Polymerization Induced Emission

Visualizing polymer chain growth is always a hot topic for tailoring structure-function properties in polymer chemistry. However, current characterization methods are limited in their ability to differentiate the degree of polymerization in real-time without isolating the samples from the reaction vessel, let alone to detect insoluble polymers. Herein, a reliable relationship is established between polymer chain growth and fluorescence properties through polymerization induced emission. (TPE-C2)2 -Te is used to realize in situ oxidative polymerization, leading to the aggregation of fluorophores. The relationship between polymerization degree of growing polytelluoxane (PTeO) and fluorescence intensity is constructed, enabling real-time monitoring of the polymerization reaction. More importantly, this novel method can be further applied to the observation of the polymerization process for growing insoluble polymer via surface polymerization. Therefore, the development of visualization technology will open a new avenue for visualizing polymer chain growth in real-time, regardless of polymer solubility.

Visible-Light-Induced Cationic Polymerization of Isobutylene: A Route toward the Synthesis of End-Functional Polyisobutylene

The visible-light-induced cationic polymerization of isobutylene with a dimanganese decacarbonyl (Mn2(CO)10)/diphenyl iodonium hexafluorophosphate (Ph2I+PF6-) photoinitiating system in a CH2Cl2/n-hexane mixture at -30 °C was reported. It was shown that polymerization is initiated by chloromethylisobutyl carbocations generated by the oxidation of chloromethylisobutyl radicals by Ph2I+PF6-. The latter are formed via chlorine abstraction from solvent (CH2Cl2) by MnCO5· radicals, which are generated by the photoinduced decomposition of Mn2(CO)10, followed by single isobutylene addition. This initiating system allowed us to synthesize valuable low molecular weight polyisobutylene with a relatively low polydispersity (Mn = 2000-3000 g mol-1; Đ < 1.7) and high content of exo-olefin end groups (up to 90%). The molecular weight of polyisobutylenes could be easily controlled in the range from 2000 to 12000 g mol-1 by changing the diphenyl iodonium salt concentration. Poly(β-pinene) with Mn = 5000 g mol-1 and Đ ∼ 2.0 was successfully synthesized using the same photoinitiating system.

Asymmetric counteranion-directed photoredox catalysis

Photoredox catalysis enables distinctive and broadly applicable chemical reactions, but controlling their selectivity has proven to be difficult. The pursuit of enantioselectivity is a particularly daunting challenge, arguably because of the high energy of the activated radical (ion) intermediates, and previous approaches have invariably required pairing of the photoredox catalytic cycle with an additional activation mode for asymmetric induction. A potential solution for photoredox reactions proceeding via radical ions would be catalytic pairing with enantiopure counterions. However, although attempts toward this approach have been described, high selectivity has not yet been accomplished. Here we report a potentially general solution to radical cation-based asymmetric photoredox catalysis. We describe organic salts, featuring confined imidodiphosphorimidate counteranions that catalyze highly enantioselective [2+2]-cross cycloadditions of styrenes.

Monophosphoniums as Effective Photoredox Organocatalysts for Visible Light-Regulated Cationic RAFT Polymerization

Visible light-regulated metal-free polymerizations have attracted considerable attention for macromolecular syntheses in recent years. However, few organic photocatalysts show high efficiency and strict photocontrol in cationic polymerizations. Herein, we introduce monophosphonium-doped polycyclic arenes as an organic photocatalyst, which features the high tunability, broad redox window, long excited state lifetime, and excellent temporal control in the cationic reversible addition-fragmentation chain transfer polymerization of vinyl ethers. A correlation of the catalytic performance and the photophysical and electrochemical properties of photocatalysts is also discussed.