The coupling of mechanical forces with chemical phenomena at the molecular level has led to a renaissance in the field of mechanochemistry.In recent years,the emergence of novel polymerization technologies involving temperature,light,electricity,and other external field regulations has highlighted mechanical force as a productive pathway.Mechanochemical routes in chemical synthesis minimize the use of potentially harmful solvents and enable the synthesis of materials through reaction pathways that are challenging to access via thermal or light-activated processes.These routes include mechanical degradation,activation,catalysis,and initiation under harsh conditions to drive chemical transformation in organic or polymer chemistry.Since Staudinger discovered the mechanical degradation of polymer chains during the polymer mixing process,the destructive effects of mechanical force on polymers have been intensively investigated.With the development of mechanochemistry,researchers observed that the cleavage of covalent bonds in the polymer main chain induced by mechanical force generates active macromolecular radicals,thereby enabling the conversion of mechanical force from destructive to productive.Consequently,the relationship between polymer mechanochemistry and radical chemistry has been established.While mechanical force serves as an external stimulus enabling the degradation and modification of polymers,progress in regulating polymer synthesis has been sluggish.Currently,most reported polymerization reactions still rely on substantial quantities of solvents in the liquid phase or the heating of solid monomers to their molten states.In recent years,the intersection of mechanochemistry and controlled radical polymerization(CRP)has witnessed rapid development,providing new insights into polymer science.Nowadays,mechanochemical controlled radical polymeriza-tion(mechano-CRP)can be realized by many methods,such as sonochemical atom transfer radical polymerization(ATRP),piezoelectric catalytic ATRP,piezoelectric catalytic reversible addition-fragmentation chain transfer(RAFT)polymerization,and contact electrocatalytic ATRP.Mechanical force,as a reliable external field control method,is widely used to initiate free radical polymerization.Benefiting from the existing reversible-deactivation radical polymerization(RDRP)systems,researchers have achieved control of the structure,molecular weight and molecular weight distribution of products.These significant advances have effectively promoted the development of RDRP controlled by external fields.As an effective control method,mechanical force is expected to effectively complement external field control methods such as light,heat,and electricity.Although mechano-CRP has made significant progress,there are still some critical problems to be solved,mainly in the following aspects.(1)High energy input:Most systems need high-frequency ultrasound or high-energy ball milling driven polymerization,which easily causes side reactions such as macromolecular chain degradation,making it challenging to prepare high molecular weight polymers.(2)Inert atmosphere:The current mechano-RDRP system is not compatible with oxygen,so it needs to be carried out under inert gas,especially for magnified reactions which require high-end equipment.(3)Impurities:Mechano-RDRP based on the piezoelectric effect or contact electric effect requires the introduction of a large number of inorganic particles as mechanochemical conversion units to realize the energy conversion of mechanical energy,electric energy and chemical energy.A lot of impurities will inevitably be introduced,which puts higher requirements on the post-treatment of polymer products,making it difficult to apply to the preparation of polymer hybrids/composites.Overall,mechanochemically controlled radical polymerization is a promising method,but it still requires further efforts for a comprehensive and in-depth understanding.In this perspective,we review the historical development of mechanochemical radical polymerization and focus on the recent progress of force-mediated radical polymerization.We aim to clarify its critical scientific problems and hope to point out the direction for the innovation and development of a new mechanochemical radical polymerization system.
mechanochemistrypolymer chemistryexternal field regulationcontrolled radical polymerization
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