Mechanoredox processes, which involve mechanically induced electron transfer, have recently gained significant interest in organic synthesis and biological applications. For macromolecule synthesis, mechanoredox processes utilize force as an alternative energy source to conventional thermal and photochemical systems. However, current mechanoredox mediated polymerization systems often require transition metal additives and show limited control over background activity. Herein, we demonstrate a metal free mechanoredox mediated radical polymerization based on aryl iodonium salts and piezonanoparticles (PNPs). Iodonium salts initiated both free radical polymerization (FRP) and controlled reversible addition-fragmentation chain-transfer (RAFT) polymerization of meth(acrylate) monomers by utilizing ultrasound (US) and ball mill as force (see figure). In the FRP system, high molecular weight polymers were achieved with typical FRP molecular weight distribution (PDI = 1.5-2). On the other hand, in the RAFT system, very good control over the molecular weight was observed (PDI~1.05). Chain end analysis was carried out by high resolution MALDI to confirm the mechanism. Additionally, in both cases, the effects of the PNP loading and nature of the PNPs on polymerization rate were studied. Pleasantly, in the absence of mechanoredox conditions, no significant background activity was realized. The developed methodology can be crucial for mechanically induced post polymerization modification and adaptive material design.

Piezonanoparticles and aryl onium salts facilitate metal free mechanoredox process for free and controlled radical polymerization

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