Ko Kwangwook, Lundberg David J, Johnson Alayna M, Johnson Jeremiah A
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
J Am Chem Soc. 2024 Apr 3;146(13):9142-9154. doi: 10.1021/jacs.3c14554. Epub 2024 Mar 25.
The development of cleavable comonomers (CCs) with suitable copolymerization reactivity paves the way for the introduction of backbone deconstructability into polymers. Recent advancements in thionolactone-based CCs, exemplified by dibenzo[c,e]-oxepine-5(7H)-thione (DOT), have opened promising avenues for the selective deconstruction of multiple classes of vinyl polymers, including polyacrylates, polyacrylamides, and polystyrenics. To date, however, no thionolactone CC has been shown to copolymerize with to an appreciable extent to enable polymer deconstruction. Here, we overcome this challenge through the design of a new class of benzyl-functionalized thionolactones (bDOTs). Guided by detailed mechanistic analyses, we find that the introduction of radical-stabilizing substituents to bDOTs enables markedly increased and tunable copolymerization reactivity with methyl methacrylate (MMA). Through iterative optimizations of the molecular structure, a specific bDOT, , is discovered to copolymerize efficiently with MMA. High molar mass deconstructable PMMA-based copolymers (dPMMA, > 120 kDa) with low percentages of (1.8 and 3.8 mol%) are prepared using industrially relevant bulk free radical copolymerization conditions. The thermomechanical properties of dPMMA are similar to PMMA; however, the former is shown to degrade into low molar mass fragments (<6.5 kDa) under mild aminolysis conditions. This work presents the first example of a radical ring-opening CC capable of nearly random copolymerization with MMA without the possibility of cross-linking and provides a workflow for the mechanism-guided design of deconstructable copolymers in the future.
具有合适共聚反应活性的可裂解共聚单体（CCs）的开发为将主链可解构性引入聚合物铺平了道路。以二苯并[c,e]-氧杂环庚烷-5(7H)-硫酮（DOT）为代表的基于硫代内酯的CCs的最新进展为包括聚丙烯酸酯、聚丙烯酰胺和聚苯乙烯类在内的多种乙烯基聚合物的选择性解构开辟了有前景的途径。然而，迄今为止，尚未有硫代内酯CC被证明能与[具体物质未给出]以可观的程度共聚以实现聚合物解构。在此，我们通过设计一类新型的苄基官能化硫代内酯（bDOTs）克服了这一挑战。在详细的机理分析指导下，我们发现向bDOTs引入自由基稳定取代基可显著提高并调节与甲基丙烯酸甲酯（MMA）的共聚反应活性。通过对分子结构的迭代优化，发现一种特定的bDOT，[具体bDOT未给出]，能与MMA高效共聚。使用工业相关的本体自由基共聚条件制备了具有低百分比[具体物质未给出]（1.8和3.8 mol%）的高摩尔质量可解构的基于聚甲基丙烯酸甲酯的共聚物（dPMMA，[具体数值未给出]>120 kDa）。dPMMA的热机械性能与聚甲基丙烯酸甲酯相似；然而，前者在温和的氨解条件下会降解为低摩尔质量片段（<6.5 kDa）。这项工作展示了第一个能够与MMA几乎无规共聚且不存在交联可能性的自由基开环CC的实例，并为未来可解构共聚物的机理导向设计提供了一个工作流程。
