力化学调控自由基聚合

Mechanochemically mediated controlled radical polymerization

力化学探究物质在机械力作用下发生的化学和物理化学变化,通过机械力反应,可以制备传统方法难以获得的材料,并且有望减少有机溶剂的使用,促进绿色化学的发展.近年来,力化学与可控自由基聚合领域的交叉研究迅速发展,为高分子科学提供了新的思路和方法.这一领域已经取得了一系列重要的进展,开创了基于超声化学、压电催化和接触电催化的力化学调控自由基聚合技术,不仅能够实现高分子量聚合物的制备,还能实现外力对聚合物链长和结构的精确控制.然而,当前力化学调控的自由基聚合仍存在一些关键问题需要解决,如副反应、氧气不兼容性和引入大量无机颗粒等,限制了其进一步应用.本文回顾了力化学的历史和高分子力化学的发展,综述了力化学调控自由基聚合的研究进展,并探讨了该领域面临的问题与挑战.

The coupling of mechanical forces with chemical phenomena at the molecular level has led to a renaissance in the field ofmechanochemistry. 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 synthesisof materials through reaction pathways that are challenging to access via thermal or light-activated processes. These routesinclude mechanical degradation, activation, catalysis, and initiation under harsh conditions to drive chemicaltransformation in organic or polymer chemistry.Since Staudinger discovered the mechanical degradation of polymer chains during the polymer mixing process, thedestructive effects of mechanical force on polymers have been intensively investigated. With the development ofmechanochemistry, researchers observed that the cleavage of covalent bonds in the polymer main chain induced bymechanical force generates active macromolecular radicals, thereby enabling the conversion of mechanical force fromdestructive to productive. Consequently, the relationship between polymer mechanochemistry and radical chemistry hasbeen established. While mechanical force serves as an external stimulus enabling the degradation and modification ofpolymers, progress in regulating polymer synthesis has been sluggish. Currently, most reported polymerization reactionsstill 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 rapiddevelopment, providing new insights into polymer science. Nowadays, mechanochemical controlled radical polymerization(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 widelyused 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 ofproducts. These significant advances have effectively promoted the development of RDRP controlled by external fields. Asan effective control method, mechanical force is expected to effectively complement external field control methods such aslight, heat, and electricity. Although mechano-CRP has made significant progress, there are still some critical problems tobe solved, mainly in the following aspects. (1) High energy input: Most systems need high-frequency ultrasound or highenergyball 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-RDRPsystem is not compatible with oxygen, so it needs to be carried out under inert gas, especially for magnified reactions whichrequire high-end equipment. (3) Impurities: Mechano-RDRP based on the piezoelectric effect or contact electric effectrequires the introduction of a large number of inorganic particles as mechanochemical conversion units to realize theenergy conversion of mechanical energy, electric energy and chemical energy. A lot of impurities will inevitably beintroduced, which puts higher requirements on the post-treatment of polymer products, making it difficult to apply to thepreparation of polymer hybrids/composites. Overall, mechanochemically controlled radical polymerization is a promisingmethod, 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 therecent progress of force-mediated radical polymerization. We aim to clarify its critical scientific problems and hope to pointout the direction for the innovation and development of a new mechanochemical radical polymerization system.