Go Eun Sul, Hong Eun Ji, Lee Ji Yeong, Stolar Tomislav, Peterson Gregory I, Emmerling Franziska L, Kim Kyoungsoo, Kim Jeung Gon
Department of Chemistry, Jeonbuk National University, Jeonju 54896, Republic of Korea.
BAM Federal Institute for Materials Research and Testing, Richard-Willstätter-Strasse11, 12489 Berlin, Germany.
JACS Au. 2025 May 29;5(6):2720-2727. doi: 10.1021/jacsau.5c00322. eCollection 2025 Jun 23.
As mechanochemical synthesis has advanced significantly, there has been intense interest in understanding the underlying mechanisms of these reactions. Given that many mechanochemical processes are conducted in the solid-state without solvation yet sometimes yield faster reactions than those in solution, we sought to address the following question: Are mechanochemical reactions homo- or heterogeneous? To investigate, we employed a model system involving the mixing and copolymerization of l-lactide (LLA) and d-lactide (DLA), monitored through powder X-ray diffraction (PXRD), nuclear magnetic resonance, and differential scanning calorimetry. and PXRD analyses of the mixture of LLA and DLA showed that vibratory ball milling rapidly transformed the initially heterogeneous lactide mixture into a homogeneous phase within one min due to collisions between the balls and the jar. By varying the milling conditions, we were able to regulate the level of mixing, which subsequently influenced the copolymerization outcomes. In the solid-state ball-milling copolymerization of LLA and DLA in the presence of a catalyst and initiator, multiblock copolymers of poly-(l-lactic acid) and poly-(d-lactic acid) were formed within one min during the early stage of the reaction, when incomplete mixing of the monomers led to a process governed by phase heterogeneity. In contrast, prolonged polymerization promoted conditions approaching homogeneity, ultimately yielding atactic poly-(lactic acid). This transition from heterogeneous to homogeneous reactions is a distinctive feature compared to conventional homogeneous reactions, potentially leading to mechano-exclusive reaction designs.
随着机械化学合成取得显著进展，人们对理解这些反应的潜在机制产生了浓厚兴趣。鉴于许多机械化学过程是在固态下进行且无溶剂化作用，但有时却比溶液中的反应更快，我们试图解决以下问题：机械化学反应是均相的还是非均相的？为了进行研究，我们采用了一个模型体系，该体系涉及左旋丙交酯（LLA）和右旋丙交酯（DLA）的混合及共聚反应，并通过粉末X射线衍射（PXRD）、核磁共振和差示扫描量热法进行监测。对LLA和DLA混合物的PXRD分析表明，由于球与研磨罐之间的碰撞，振动球磨在一分钟内迅速将最初的非均相丙交酯混合物转变为均相。通过改变研磨条件，我们能够调节混合程度，进而影响共聚反应结果。在有催化剂和引发剂存在的情况下，LLA和DLA的固态球磨共聚反应中，在反应早期的一分钟内，当单体混合不完全导致反应受相非均质性控制时，形成了聚（左旋乳酸）和聚（右旋乳酸）的多嵌段共聚物。相比之下，延长聚合时间会促使反应条件接近均相，最终生成无规聚（乳酸）。与传统均相反应相比，这种从非均相反应到均相反应的转变是一个独特的特征，可能会导致机械化学独有的反应设计。
