Peng Yong-Jin, Cai Chen-Ting, Wang Chang-Jun, Zuo Zhong-Fu, Liu Xue-Zheng
College of Comprehensive Studies, Jinzhou Medical University Jinzhou 121001 P. R. China.
College of Chemistry, Nankai University Tianjin 300071 P. R. China.
RSC Adv. 2019 May 16;9(27):15318-15322. doi: 10.1039/c9ra01942a. eCollection 2019 May 14.
Understanding the nature of glass transition is still a great challenge. Glass transition is widely observed in many glassy materials; however, it has never been unambiguously observed in reversible cross-linked polymer, which is an ideal model of the percolation process. Herein, we report the synthesis of a reversible cross-linked polymer incorporated with four-armed Diels-Alder (DA) dynamic covalent bonds, and the robust experimental observation of percolation-induced glass transition in this reversible four-armed cross-linked polymer (DAMF1). Temperature-modulated differential scanning calorimetry (TMDSC) experiment results clearly revealed the presence of a glass transition along with an endothermic or exothermic peak associated with DA/retro-DA (RDA) reaction related to the reconstitution/disassociation of the DAMF1's four-armed cross-linked network. C variable-temperature solid-state NMR experiments further confirmed the DA/RDA reaction during glass transition at a molecular level. The above experimental results provide a direct experimental evidence for the recently developed percolation model of glass transition, which provides new insights into the nature of glass transition.
理解玻璃化转变的本质仍然是一个巨大的挑战。玻璃化转变在许多玻璃态材料中广泛存在；然而，在可逆交联聚合物中从未明确观察到玻璃化转变，而可逆交联聚合物是渗流过程的理想模型。在此，我们报道了一种结合了四臂狄尔斯-阿尔德（DA）动态共价键的可逆交联聚合物的合成，以及在这种可逆四臂交联聚合物（DAMF1）中对渗流诱导的玻璃化转变的有力实验观察。温度调制差示扫描量热法（TMDSC）实验结果清楚地揭示了玻璃化转变的存在以及与DA/逆DA（RDA）反应相关的吸热或放热峰，该反应与DAMF1的四臂交联网络的重构/解离有关。变温固态核磁共振实验在分子水平上进一步证实了玻璃化转变过程中的DA/RDA反应。上述实验结果为最近发展的玻璃化转变渗流模型提供了直接的实验证据，该模型为玻璃化转变的本质提供了新的见解。
