Lin Yangju, Barbee Meredith H, Chang Chia-Chih, Craig Stephen L
Department of Chemistry , Duke University , Durham , North Carolina 27708 , United States.
J Am Chem Soc. 2018 Nov 21;140(46):15969-15975. doi: 10.1021/jacs.8b10376. Epub 2018 Nov 7.
Mechanochromic force probes, including spiropyran derivatives, have proven to be useful in visualizing the stress/strain distribution and fracture behavior in polymeric materials. Here, we report the macroscopic response of silicone elastomers including cross-links made up of three spiropyran (SP) regioisomers. The SP derivatives SP( o), SP( m), and SP( p) are connected to the network through an identical attachment point on the indoline fragment and regioisomeric attachments ortho, meta, and para to the spirocyclic C-O bond on the benzaldehyde fragment, respectively. The relative colorimetric response of these regioisomers under quasi-static uniaxial tensile load is SP( o) > SP( m) > SP( p), consistent with the expected mechanical sensitivity of the regioisomers obtained from molecular modeling. The extrapolated strain onset for detectable activation of all three regioisomers, however, is indistinguishable and occurs at ∼90% uniaxial strain. Finally, the ratiometric response of the three isomers is constant across the strains investigated (90-135% uniaxial strain), in contrast to expectations based on simulations of strained intact polymer networks.
机械变色力探针，包括螺吡喃衍生物，已被证明可用于可视化聚合物材料中的应力/应变分布和断裂行为。在此，我们报告了含由三种螺吡喃（SP）区域异构体组成的交联结构的硅氧烷弹性体的宏观响应。SP衍生物SP（o）、SP（m）和SP（p）分别通过吲哚啉片段上的相同连接点以及苯甲醛片段上与螺环C-O键邻位、间位和对位的区域异构连接点连接到网络。这些区域异构体在准静态单轴拉伸载荷下的相对比色响应为SP（o）>SP（m）>SP（p），这与通过分子建模获得的区域异构体预期机械灵敏度一致。然而，所有三种区域异构体可检测激活的外推应变起始点无法区分，且发生在约90%的单轴应变处。最后，与基于应变完整聚合物网络模拟的预期相反，三种异构体的比率响应在所研究的应变范围内（90 - 135%单轴应变）保持恒定。
