Mechanophore activation at heterointerface and surface crowdedness as a determining factor

Polymer Mechanochemistry;Interface;Grafting Density;Mechanophore

Li, Jun

关键词: Polymer Mechanochemistry;    Interface;    Grafting Density;    Mechanophore;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/90781/LI-DISSERTATION-2016.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

When bringing "mechanical force" and "polymer" into conversation, one might naturally relate to everyday scenarios such as worn cloth, broken taillight and cracked paint. The intuitive viewpoint reflects the historic consensus that mechanically induced chemical changes are destructive. Starting from 2005, several research groups reported the productive use of mechanical force in polymer mechanochemistry around the topic of mechanophore, a molecular unit that chemically responds in a selective manner to a mechanical perturbation, design and development. Most of the research is focused on mechanophore embedded polymers. However, behavior of mechanophores at heterointerfaces is particularly interesting, as interfaces in composite materials are often the weakest point where damage-reporting and self-healing are applicable. To achieve this goal, a model system was constructed to allow facile synthesis and activation characterization of mechanophore. Anthracene-maleimide cycloadduct was selected as the target mechanophore and immobilized on the surface of silica nanoparticles. Surface-initiated polymerization yielded poly (methyl acrylate) grafted mechanophore anchored silica nanoparticles. The mechanically-activated retro [4+2] cycloaddition was deliberately designed to yield the cleavage of the polymer with an anthracene end-cap. UV diode-array detector coupled gel permeation chromatography was used to confirm the selective cleavage of anthracene-containing polymer and to rigorously quantify the kinetic coefficient of mechanochemical reaction. Comparison with mechanophore embedded polymer show that both the threshold molecular weight and linear increase of kinetic coefficient against molecular weight apply for interfacial mechanophores. Furthermore, we investigated the controlling factors of interfacial mechanophore activation and found that aside from degree of polymerization, surface crowdedness of the interface largely influences the activation behavior. More specifically, the mechanophore grafted with lower density activated significantly faster than that grafted with higher grafting density. These results provide a greater understanding of mechanotransduction processes at heterogeneous interfaces and thus allow design of mechanoresponsive composite materials.Our efforts in developing a thermally and mechanically triggerable ruthenium catalyst system for material remodeling application were also discussed.