Mechanochemical ring-opening metathesis polymerization: development, scope, and mechano-exclusive polymer synthesis

Anionic ring-opening polymerization of functional epoxide monomers in the solid state

Despite recent advancements in mechanochemical polymerization, understanding the unique mechanochemical reactivity during the ball milling polymerization process still requires extensive investigations. Herein, solid-state anionic ring-opening polymerization is used to synthesize polyethers from various functional epoxide monomers. The critical parameters of the monomers are investigated to elucidate the unique reactivity of ball milling polymerization. The controllable syntheses of the desired polyethers are characterized via NMR, GPC, and MALDI-ToF analyses. Interestingly, bulky monomers exhibit faster conversions in the solid-state in clear contrast to that observed for solution polymerization. Particularly, a close linear correlation is observed between the conversion of the ball milling polymerization and melting point of the functional epoxide monomers, indicating melting point as a critical predictor of mechanochemical polymerization reactivity. This study provides insights into the efficient design and understanding of mechanochemical polymerization.

Mechanochemical Synthesis of Stimuli Responsive Microgels

Mechanochemical approaches are widely used for the efficient, solvent-free synthesis of organic molecules, however their applicability to the synthesis of functional polymers has remained underexplored. Herein, we demonstrate for the first time that mechanochemically triggered free-radical polymerization allows solvent- and initiator-free syntheses of structurally and morphologically well-defined complex functional macromolecular architectures, namely stimuliresponsive microgels. The developed mechanochemical polymerization approach is applicable to a variety of monomers and allows synthesizing microgels with tunable chemical structure, variable size, controlled number of crosslinks and reactive functional end-groups.

TM-Free and TM-Catalyzed Mechanosynthesis of Functional Polymers

Mechanochemically induced methods are commonly used for the depolymerization of polymers, including plastic and agricultural wastes. So far, these methods have rarely been used for polymer synthesis. Compared to conventional polymerization in solutions, mechanochemical polymerization offers numerous advantages such as less or no solvent consumption, the accessibility of novel structures, the inclusion of co-polymers and post-modified polymers, and, most importantly, the avoidance of problems posed by low monomer/oligomer solubility and fast precipitation during polymerization. Consequently, the development of new functional polymers and materials, including those based on mechanochemically synthesized polymers, has drawn much interest, particularly from the perspective of green chemistry. In this review, we tried to highlight the most representative examples of transition-metal (TM)-free and TM-catalyzed mechanosynthesis of some functional polymers, such as semiconductive polymers, porous polymeric materials, sensory materials, materials for photovoltaics, etc.

Mechanoredox Catalysis Enables a Sustainable and Versatile Reversible Addition-Fragmentation Chain Transfer Polymerization Process

The sustainable synthesis of macromolecules with control over sequence and molar mass remains a challenge in polymer chemistry. By coupling mechanochemistry and electron-transfer processes (i.e., mechanoredox catalysis), an energy-conscious controlled radical polymerization methodology is realized. This work explores an efficient mechanoredox reversible addition-fragmentation chain transfer (RAFT) polymerization process using mechanical stimuli by implementing piezoelectric barium titanate and a diaryliodonium initiator with minimal solvent usage. This mechanoredox RAFT process demonstrates exquisite control over poly(meth)acrylate dispersity and chain length while also showcasing an alternative to the solution-state synthesis of semifluorinated polymers that typically utilize exotic solvents and/or reagents. This chemistry will find utility in the sustainable development of materials across the energy, biomedical, and engineering communities.

Mechanochemical solid-state vinyl polymerization with anionic initiator

Mechanochemistry has been extended to various polymer syntheses to achieve efficiency, greenness, and new products. However, many fundamental polymerization reactions have not been explored, although anionic polymerization of vinyl compounds has been pursued under mechanochemical conditions. Two solid monomers, 4-biphenyl methacrylate and 4-vinyl biphenyl, representing methacrylate and styrenic classes, respectively, were reacted with secondary butyl lithium under high-speed ball-milling. The alkyl-anion-promoted polymerization process was established by excluding radical initiation and producing the expected polymers with good efficiency. However, the generally expected features of anionic polymerization, such as molecular weight control and narrow dispersity, were not observed. Analysis of the milling parameters, reaction monitoring, and microstructural analysis revealed that the mechanism of the mechanochemical process differs from that of conventional anionic polymerizations. The mechanical force fractured the newly formed polymer chains via anionic initiation and generated macroradicals, which participated in the polymerization process. The anionic process governs the initiation step and the radical process becomes dominant during the propagation step.

Mechanochemical Synthesis of Polyanilines and Their Nanocomposites: A Critical Review

The mechanochemical synthesis of polyanilines (PANIs), made by oxidative polymerization of anilines, is reviewed. First, previous knowledge of the polymerization reaction in solution is discussed to understand the effect of different parameters: oxidant/monomer ratio, added acid, oxidant, temperature and water content on the properties of the conducting polymers (molecular weight, degradation, doping/oxidation level, conductivity, and nanostructure). The work on mechanochemical polymerization (MCP) of anilines is analyzed in view of previous data in solution, and published data are critically reconsidered to clarify the interpretation of experimental results. A key factor is the production of acids during polymerization, which is often overlooked. The production of gaseous HCl during MCP of aniline hydrochloride is experimentally observed. Since some experiments involves the addition of small amounts of water, the kinetics and heat balance of the reaction with concentrated solutions were simulated. A simple experiment shows fast (<2 min) heating of the reaction mixture to the boiling point of water and temperature increments are observed during MCP in a mortar. The form and sizes of PANI nanostructures made by MCP or solution are compared. The extensive work on the production of nanocomposites by MCP of anilines together with different nanomaterials (porous clays, graphene, carbon nanotubes, metal, and oxide nanoparticles) is also described.