Mechanically Initiated Bulk‐Scale Free‐Radical Polymerization

Abstract

Mechanical initiation of polymerization offers the chance to generate polymers in new environments using an energy source with unique capabilities. Recently, a renewed interest in mechanically controlled polymerization has yielded many techniques for controlled radical polymerization by ultrasound. However, other types of polymerizations induced by mechanical activation are rare, especially for generating high‐molecular‐weight polymers. Herein is an example of using piezoelectric ZnO nanoparticles to generate free‐radical species that initiate chain‐growth polymerization and polymer crosslinking. The fast generation of high amounts of reactive radicals enable the formation of polymer/gel by ultrasound activation. This chemistry can be used to harness mechanical energy for constructive purposes in polymeric materials and for controlled polymerizations for bulk‐scale reactions.

Ultrasound-Mediated Atom Transfer Radical Polymerization (ATRP)

“…The proposed mechanism assumes that Fe III located on the surface of piezoelectric facilitates the free-radical transfer during ultrasonic agitation, and thus, the piezocatalytic cleavage of alkyl halides occurs (Figure 5). It constitutes a different mechanism than in previous reports, where the predominant role of piezoelectric was to provide electrons to reduce Cu II [50].…”

“…The application of Fe III in connection with ZnO allows for the mechanically controlled free-radical polymerization and crosslinking in a one-pot fashion, and thus, more efficient consumption of ultrasound energy, making a mechanoradical polymerization potentially applicable and compatible with many conventional methods [50].…”

“…It is generated from the mechanical effect of acoustic cavitation on liquid medium resulting in the growth, formation and implosive collapse of bubbles in liquids followed by the formation of extremely high temperature and pressure conditions [45]. Considering RDRP, both reversible addition-fragmentation chain-transfer polymerization (RAFT) [46,47] and ATRP [12,40,41,42,43,48,49,50,51,52,53] successfully applied ultrasonication as an external stimulus for promoting polymerization reactions. In the field of controlled polymer synthesis, the ultrasound-mediated effect can be divided for physical sonochemistry and mechanochemistry [45,54].…”

“…ATRP uses the both of those approaches. It is considered in two different ways: mechano-ATRP (ultrasonication as a mechanical force to induce an electric charge in response to an applied mechanical strain with the use of piezoelectric) [40,41,42,48,49,50] and sono-ATRP, where the driving force of an activator’s regeneration are hydroxyl radicals in aqueous media [12,43,51] and reactive radical species from solvent/ligand/additional reagents in organic solvent [52,53]. The range of frequencies used in ATRP covers mainly low frequencies (20–40 kHz); however, the higher frequencies (490 kHz) have been also investigated.…”

Post‐Polymerization Thiol Substitutions Facilitated by Mechanochemistry

“…In the realm of polymer science, mechanochemistry has often been used as a tool for the controlled chain scission of macromolecules containing mechanophores . However, there are examples that describe the use of mechanochemistry to facilitate polymer synthesis . An idea that has been investigated to a lesser extent is the use of mechanochemistry to facilitate post‐polymerization modification reactions.…”