Exploiting Visible-Light Induced Radical to Cation Transformation Pathway for Reactivity Enhanced Electrophilic Aromatic Substitution Polymerization of Heteroaromatics.

A straightforward approach is employed to synthesize methylene-bridged poly(hetero aromatic)s based on furan, pyrrole, thiophene, and thiophene derivatives. The process involves an electrophilic aromatic substitution reaction facilitated by a visible light-initiated system consisting of manganese decacarbonyl and an iodonium salt. The approach mainly relies on the formation of halomethylium cation, the attack of this cation to heteroaromatic, regeneration of methylium cation on the heteroaromatic, and reactivity differences between halomethylium and heteroaromatic methylium cations for successful polymerizations. This innovative synthetic strategy lead to the formation of polymers with relatively high molecular weights as the stoichiometric imbalance between the comonomers increased. Accordingly, these newly obtained polymers exhibit remarkable fluorescence properties, even at excitation wavelengths as low as 330 nm. Moreover, by harnessing the halogens at chain ends of homopolymers, block copolymers are successfully synthesized, offering opportunities for tailored applications in diverse fields.

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; D < 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(ß-pinene) with Mn = 5000 g mol-1 and D ∼ 2.0 was successfully synthesized using the same photoinitiating system.

Visible Light Induced Degradation of Poly(methyl methacrylate-co-methyl α-chloro acrylate) Copolymer at Ambient Temperature.

Poly(methyl methacrylate) (PMMA) is a well-known and widely used commodity plastic. High production amount of PMMA causes excessive waste creation that highlights the necessity of recycling. Conventional recycling methods require elevated temperatures to induce degradation or depolymerization. In this work, visible light induced photodegradation system by using dimanganese decacarbonyl (Mn2 (CO)10 ) with high halogen affinity is reported. Halide functional photodegradable polymers are prepared by copolymerization of methyl methacrylate and methyl α-chloroacrylate by conventional reversible addition-fragmentation chain-transfer polymerization. Synthesized copolymers are efficiently degraded to low molecular weight oligomers under visible light irradiation in the presence of Mn2 (CO)10 . Characteristics of precursors, degraded polymers, and kinetics of depolymerization are investigated by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourrier transform infrared (FTIR), and proton nuclear magnetic resonance (1 H-NMR) spectroscopies. The reported approach is expected to trigger further development of more environmentally friendly recycling techniques in the near future as we  are moving toward a greener and more sustainable world.

Photoinitiated Cationic Ring-Opening Polymerization of Octamethylcyclotetrasiloxane.

Photochemical techniques have recently been revitalized as they can readily be adapted to different polymerization modes to yield a wide range of complex macromolecular structures. However, the implementation of the photoinduced cationic methods in the polymerization of cyclic siloxane monomers has scarcely been investigated. Octamethylcyclotetrasiloxane (D4) is an important monomer for the synthesis of polydimethylsiloxane (PDMS) and its copolymers. In this study, the cationic ring-opening polymerization (ROP) of D4, initiated by diphenyl iodonium hexafluorophosphate (DPI), has been studied. Both direct and indirect initiating systems acting at broad wavelength using benzophenone and pyrene were investigated. In both systems, photochemically generated protonic acids and silylium cations are responsible for the polymerization. The kinetics of the polymerization are followed by viscosimetry and GPC analyses. The reported approach may overcome the problems associated with conventional methods and therefore represents industrial importance for the fabrication of polysiloxanes.

Visible Light Induced High Resolution and Swift 3D Printing System by Halogen Atom Transfer.

3D printing technology offers solutions for numerous needs in industry and the daily life of individuals. In recent years, most research efforts have focused on this technology as the market share has grown and requirements have become specified in their related fields. In this work, a novel visible light induced 3D printing system with high resolution and short printing time using dimanganese decacarbonyl (Mn2 (CO)10 ) in combination with organic halides is reported. The radicals formed through halogen abstraction by photochemically generated manganese pentacarbonyl from organic halides with high quantum efficiency initiate the polymerization of acrylic resins. The kinetics of the process using various halide-containing molecules in the photoinitiaiting system are investigated with real-time fourrier transform infrared spectroscopy and photo-differential scanning calorimetry analyses, and the characteristics of 3D printouts are presented and compared with that of the commercial photoinitiator, 2,4,6-trimethylbenzoyl)phosphine oxide without Mn2 (CO)10 . The results obtained confirm that the combination of Mn2 (CO)10 and structurally diverse organic halides is a class of promising 3D system for various applications.

Dimanganese decacarbonyl catalyzed visible light induced ambient temperature depolymerization of poly(methyl methacrylate).

Recent years have witnessed an enormous development in photoinduced systems, opening up possibilities for advancements in industry and academia in terms of green chemistry providing environmentally friendly conditions and spatiotemporal control over the reaction medium. A vast number of research have been conducted on photoinduced systems focusing on the development of new polymerization methods, although scarcely investigated, depolymerization of the synthesized polymers by photochemical means is also possible. Herein, we provide a comprehensive study of visible light induced dimanganese decacarbonyl (Mn2(CO)10) assisted depolymerization system for poly(methyl methacrylate) with chlorine chain end prepared by Atom Transfer Radical Polymerization. Contrary to the conventional procedures demanding high temperatures, the approach offers ambient temperature for the photodepolymerization process. This novel light-controlled concept is easily adaptable to macroscales and expected to promote further research in the fields matching with the environmental concerns.

Visible Light Induced Conventional Step-Growth and Chain-Growth Condensation Polymerizations by Electrophilic Aromatic Substitution.

A novel visible light induced step-growth polymerization by electrophilic aromatic substitution between photochemically generated carbocations and dimethoxybenzene nucleophile is described. Conventional step-growth polymerization and chain-growth condensation polymerization (CCP) mechanisms are presented. It is found that by changing the molar ratios of the monomers slightly, the CCP mechanism becomes operative and relatively higher molecular weight polymers are obtained because of the higher reactivity of the end groups of the intermediates and oligomers than that of the monomers. The possibility of grafting onto polymers containing epoxide at their side chains by photoinduced chain end activation of poly(dimethoxyphenylene methylene) is demonstrated. This study is expected to promote potential applications of the combination of photoinduced electron transfer reactions and CCP in macromolecular synthesis and material science.

Visible light induced step-growth polymerization by electrophilic aromatic substitution reactions.

A novel visible light induced step-growth polymerization to form poly(phenylene methylene) by electrophilic aromatic substitution reactions is described. The effect of different nucleophilic aromatic molecules on polymerization has been investigated. The possibility of combining step-growth polymerization with conventional free radical and free radical promoted cationic polymerizations through photoinduced chain-end activation has been demonstrated. Highly fluorescent fibers of the resulting block copolymers were obtained using the electrospinning technique. The versatile photoinduced step-growth polymerization process reported herein paves the way for a new generation of polycondensates and their combination with chain polymers that cannot be obtained by conventional methods.

Visible Light Induced Step-Growth Polymerization by Substitution Reactions.

A new visible light induced step-growth polymerization of dibromoxylene, and diols using dimanganese decacarbonyl and diphenyliodonium salt is described. The polymerization is suggested to proceed by substitution reaction between dixylenium cations formed upon visible light irradiation in the presence of dimanganese decacarbonyl and diphenyl iodonium salt. For the described substitution reaction with diols as nucleophilic component, the scope of the process is studied. Furthermore, the presence of halide groups at chain ends of the resulting polymers provided the possibility of initiating subsequent free radical and free radical promoted cationic resulting in the formation of polyether-based block copolymers.