Dynamic Memory Effects in the Mechanochemistry of Cyclic Polymers
Dynamic Memory Effects in the Mechanochemistry of Cyclic Polymers
复制标题
DOI：
10.1021/jacs.9b03564
复制
发表时间：
2019-07-17
影响因子：
15
通讯作者：
Craig, Stephen L.
中科院分区：
文献类型：
--
作者：
Lin, Yangju;Zhang, Yudi;Craig, Stephen L.
采用扩环复分解聚合法制备了主链上沿着含有多个偕二氯环丙烷（gDCC）力学活性基团的环状聚合物。利用脉冲超声处理研究了环状聚合物的机械力化学。将每个链减半事件（Phi）活化的gDCC机械载体的分数与线性类似物的分数进行比较。对于167 kDa环状聚合物，Phi = 0.38，而对于158 kDa线性聚合物类似物，Phi = 0.62，即使环状链断裂必然通过与初始线性系统组成相当的线性中间体进行。机械化学产物的臭氧分解进一步表明，环状聚合物中的机械化学“活化区”比线性聚合物中的连续性更低。这些结果表明，在环状聚合物断裂的线性中间体在相同的高应变率拉伸事件中，它是形成的，并进一步保留至少部分的记忆，其原始的环状构象在断裂的时间进行随后的断裂。
Cyclic polymers containing multiple gem-dichlorocyclopropane (gDCC) mechanophores along their backbone were prepared using ring expansion metathesis polymerization. The mechanochemistry of the cyclic polymers was investigated using pulsed ultrasonication. The fraction of gDCC mechanophores that are activated per chain halving event (Phi) was compared to that of linear analogs. For 167 kDa cyclic polymer, Phi = 0.38, vs Phi = 0.62 for 158 kDa linear polymers analogs, even though cyclic chain fragmentation necessarily proceeds through a linear intermediate of comparable composition to the initially linear systems. Ozonolysis of the mechanochemical products further shows that the mechanochemical "activation zone" in the cyclic polymer is less continuous than in the linear polymer. These results suggest that the linear intermediate in cyclic polymer fragmentation undergoes subsequent scission during the same high strain rate extensional event in which it is formed and furthermore retains at least a partial memory of its original cyclic conformation at the time of fragmentation.