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

Abstract

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.

Mechanochemically mediated controlled radical polymerization

“…球磨碰撞产生的自由基能够引发自由基聚合反应 [94] ，但通常伴随着剧烈碰撞导 致的机械降解事件 [95] ，目前仍没有有效的办法来防止机械降解的发生。这种现 象限制了机械力在合成聚合物方面的应用，也明确了需要开发更加高效的方式 实现低能量机械力驱动的可控自由基聚合反应。2023 年，庞新厂团队 [92] 报道了 在球磨条件下进行的压电 ATRP 反应，球磨产生的强烈共混效应有利于电子转 磨压电 RAFT 聚合反应方面也取得了重要进展，Golder 课题组 [93] 利用球磨 BaTiO 3 过程中产生的氧化还原电势差解离二芳基鎓盐，进而产生自由基引发聚 合反应(图 6(c)) 。Golder 及其合作者 [90] 在随后的工作中优化和扩展了这一体系， 将其扩展到可控自由基聚合，最终在 RAFT 聚合体系中表现出高于 95%的单体 转化率，和窄分子量分布(M w /M n <1.1)。 图 6(d)展示了 Golder 课题组 [90] 通过这 一技术，可控地合成了含有两种不相溶单体( 乙氧基乙氧基乙基丙烯酸酯 (DEGEEA)和丙烯酸六氟丁酯(HFBA) )的两亲性嵌段共聚物，这意味着力 化学方法有潜力完成溶液中无法实现的高分子合成。此外，Golder 及其合作者…”

“…A c c e p t e d https://engine.scichina.com/doi/10.1360/TB-2024-0311 [90] 还探究了球磨罐体中的氧气对聚合反应的影响，这一引发体系在未严格除氧 的条件下，表现出了较长的聚合诱导期(约 1 h) ，考虑到封闭罐体中有限的氧 气含量，实验结果仅能表明这一引发体系具有消耗氧气，重新启动聚合的特点。 图 6 球磨条件下的自由基聚合。 (a)机械球磨实现 2-乙烯基萘固态 ATRP [91] ； (b)球磨条件下进行压电 ATRP 反应 [92] ； (c)球磨或超声 BaTiO 3 解离二芳基 鎓盐产生自由基引发聚合反应 [93] ；( d)压电 RAFT 聚合 [90] Figure 6 Radical polymerization by ball milling. (a) ATRP of 2-vinylnaphthalene [91] ;…”

“…具有重要意义。Golder 课题组 [90] 在 2022 年报道了超声 BaTiO 3 氧化还原二芳基 鎓盐(二苯碘六氟磷酸盐)形成苯基自由基的引发体系，相比于王召课题组 [88] 报道的首例超声压电 导 ATRP 反应 [83] ；( b)低 ppm 铜催化剂及低频超声实现丙烯酸酯类单体 ATRP 反应 [84] ；( c)低含量 ZnO 加速固-液界面的力致电子转移过程增强诱导 ATRP 反 应 [85] ； (d)超声介导三元异质结压电性能引发 ATRP 制备力致发光复合材料 [86] ； (e)基于铁配位物(Fe-TDA)催化的 ATRP 聚合体系 [87] ；( f)基于压电效应…”

Democratization of Sono-RAFT: Reversible-Deactivation Radical Polymerization with Low-Frequency Ultrasound

“…These methods rely on an equilibrium between active and dormant chains, achieved through reversible termination and/or degenerative chain transfer, leading to polymers with controlled molecular weights and narrow molecular weight distributions . Reversible addition–fragmentation chain-transfer (RAFT) polymerization utilizes a chain-transfer agent (CTA) with the general structure of Z–C­(S)­S–R to establish equilibrium via degenerative chain transfer and requires an exogenous radical source to initiate polymerization. − Previous reports have demonstrated that initiating radicals can be generated from diverse sources, including photo, − electrochemical, , and mechanical (i.e., ultrasound, − piezoelectric, , and mechanoredox) , stimuli.…”

“…1 Reversible addition− fragmentation chain-transfer (RAFT) polymerization utilizes a chain-transfer agent (CTA) with the general structure of Z− C(�S)S−R to establish equilibrium via degenerative chain transfer and requires an exogenous radical source to initiate polymerization. 1−6 Previous reports have demonstrated that initiating radicals can be generated from diverse sources, including photo, 7−10 electrochemical, 11,12 and mechanical (i.e., ultrasound, 13−15 piezoelectric, 16,17 and mechanoredox) 18,19 stimuli.…”