Messmer Daniel, Bertran Oscar, Kissner Reinhard, Alemán Carlos, Schlüter A Dieter
Polymer Chemistry , Department of Materials , ETH Zürich , Vladimir-Prelog-Weg 5 , 8093 Zürich , Switzerland . Email:
Department of Physics , EETAC , Universitat Politècnica de Catalunya , c/ Esteve Terrades, 7 , 08860 , Castelldefels , Spain.
Chem Sci. 2019 May 8;10(24):6125-6139. doi: 10.1039/c9sc01639b. eCollection 2019 Jun 28.
We present a comprehensive investigation of main-chain scission processes affecting peripherally charged and neutral members of a class of dendronized polymers (DPs) studied in our laboratory. In these thick, sterically highly congested macromolecules, scission occurs by exposure to solvents, in some cases at room temperature, in others requiring modest heating. Our investigations rely on gel permeation chromatography and atomic force microscopy and are supported by molecular dynamics simulations as well as by electron paramagnetic resonance spectroscopy. Strikingly, DP main-chain scission depends strongly on two factors: first the solvent, which must be highly polar to induce scission of the DPs, and second the dendritic generation . In DPs of generations 1 ≤ ≤ 8, scission occurs readily only for = 5, no matter whether the polymer is charged or neutral. Much more forcing conditions are required to induce degradation in DPs of ≠ 5. We propose solvent swelling as the cause for the main-chain scission in these individual polymer molecules, explaining in particular the strong dependence on : < 5 DPs resemble classical polymers and are accessible to the strongly interacting, polar solvents, whereas > 5 DPs are essentially closed off to solvent due to their more closely colloidal character. = 5 DPs mark the transition between these two regimes, bearing strongly sterically congested side chains which are still solvent accessible to some degree. Our results suggest that, even in the absence of structural elements which favour scission such as cross-links, solvent swelling may be a generally applicable mechanochemical trigger. This may be relevant not only for DPs, but also for other types of sterically strongly congested macromolecules.
我们对影响在我们实验室中研究的一类树枝状聚合物（DPs）的外围带电和中性成员的主链断裂过程进行了全面研究。在这些厚实、空间位阻高度拥挤的大分子中，通过暴露于溶剂会发生断裂，在某些情况下是在室温下，在其他情况下则需要适度加热。我们的研究依赖于凝胶渗透色谱法和原子力显微镜，并得到分子动力学模拟以及电子顺磁共振光谱的支持。引人注目的是，DP的主链断裂强烈依赖于两个因素：首先是溶剂，它必须是高极性的才能诱导DPs的断裂；其次是树枝状代数。在1≤≤8代的DPs中，只有当=5时才容易发生断裂，无论聚合物是带电的还是中性的。对于≠5的DPs，需要更苛刻的条件才能诱导降解。我们提出溶剂溶胀是这些单个聚合物分子中主链断裂的原因，特别解释了对的强烈依赖性：<5的DPs类似于经典聚合物，可被强相互作用的极性溶剂所接触，而>5的DPs由于其更接近胶体的性质基本上对溶剂封闭。=5的DPs标志着这两种状态之间的转变，带有空间位阻高度拥挤的侧链，在一定程度上仍然可被溶剂接触。我们的结果表明，即使在没有有利于断裂的结构元素（如交联）的情况下，溶剂溶胀也可能是一种普遍适用的机械化学触发因素。这可能不仅与DPs相关，也与其他类型的空间位阻强烈拥挤的大分子相关。
