Sowan Nancy, Song Han Byul, Cox Lewis M, Patton James R, Fairbanks Benjamin D, Ding Yifu, Bowman Christopher N
Materials Science and Engineering Program, University of Colorado, Boulder, CO, 80309-0596, USA.
Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO, 80309-0596, USA.
Adv Mater. 2021 Feb;33(5):e2007221. doi: 10.1002/adma.202007221. Epub 2020 Dec 23.
A covalent adaptable network (CAN) with high glass transition temperature (T ), superior mechanical properties including toughness and ductility, and unprecedented spatio-temporally controlled dynamic behavior is prepared by introducing dynamic moieties capable of reversible addition fragmentation chain transfer (RAFT) into photoinitiated copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC)-based networks. While the CuAAC polymerization yields glassy polymers composed of rigid triazole linkages with enhanced toughness, the RAFT moieties undergo bond exchange leading to stress relaxation upon light exposure. This unprecedented level of stress relaxation in the glassy state leads to numerous desirable attributes including glassy state photoinduced plasticity, toughness improvement during large deformation, and even photoinduced reversal of the effects of physical aging resulting in the rejuvenation of mechanical and thermodynamic properties in physically aged RAFT-CuAAC networks that undergo bond exchange in the glassy state. Surprisingly, when an allyl-sulfide-containing azide monomer (AS-N ) is used to form the network, the network exhibits up to 80% stress relaxation in the glassy state (T - 45 °C) under fixed displacement. In situ activation of RAFT during mechanical loading results in a 50% improvement in elongation to break and 40% improvement in the toughness when compared to the same network without light-activation of RAFT during the tensile testing.
通过将能够进行可逆加成-断裂链转移（RAFT）的动态基团引入基于光引发的铜（I）催化叠氮化物-炔烃环加成反应（CuAAC）的网络中，制备出一种具有高玻璃化转变温度（T）、包括韧性和延展性在内的优异机械性能以及前所未有的时空可控动态行为的共价自适应网络（CAN）。虽然CuAAC聚合产生由具有增强韧性的刚性三唑键组成的玻璃态聚合物，但RAFT基团会发生键交换，导致光照时应力松弛。这种在玻璃态下前所未有的应力松弛水平带来了许多理想的特性，包括玻璃态光致可塑性、大变形过程中韧性的提高，甚至物理老化效应的光致逆转，从而使在玻璃态下发生键交换的物理老化RAFT-CuAAC网络的机械和热力学性能得以恢复活力。令人惊讶的是，当使用含烯丙基硫醚的叠氮化物单体（AS-N）形成网络时，该网络在固定位移下的玻璃态（T - 45°C）中表现出高达80%的应力松弛。与在拉伸测试期间未对RAFT进行光活化的相同网络相比，在机械加载过程中原位活化RAFT会使断裂伸长率提高50%，韧性提高40%。
