Spiropyran (SP) is an effective mechanophore because it is easy to be covalently incorporated into polymers and capable of changing color upon mechanical loading. SP motif is a model mechanophore in fundamental studies of mechanochemistry. Therefore, it is of great significance to gain a deep and comprehensive knowledge of SP mechanochemistry for the exploration of mechanochemistry in general. In the beginning of this thesis, a review of SP mechanophore was presented from an engineering perspective. A workflow for SP mechanochemistry, applications in various polymeric systems, impacting factors and characterization techniques as well as conclusions were thoroughly presented. The review aimed to offer deep insight into polymer mechanochemistry and provide approaches to study other mechanophores using the example of SP mechanochemistry in polymers.
So far there have been three types of SP mechanophores (SP1, SP2 and SP3) reported in the literature. SP1 and SP2 are sensitive to both UV light and mechanical force, whereas SP3 is sensitive to mechanical force but not to UV, which is an excellent candidate for outdoor applications. Due to the unique feature of SP3, this project is mainly focused on applying SP3 mechanophore into functional and structural polymeric materials.
• We designed and synthesized divinyl SP3 mechanophore cross-linker, which can be employed in chain growth polymerization, accounting for more than 80% of total polymer products. As a demonstration, SP3 was incorporated as a cross-linker in the free radical polymerization of methyl acrylate (MA). The mechanoactivation and UV activation of SP3-cross-linked PMA were investigated in details.
• SP3 mechanophore cross-linker was covalently incorporated into two widely used polyolefins through facile cross-linking. It represents the first example of smart polyolefins that feel the force by color changing, opening the possibilities of applying SP mechanophore into widely used polyolefin materials, accounting for more than half of the total polymer materials.
• We prepared force sensitive acrylic latex coating via covalent incorporation of SP3 mechanophore cross-linker. It is the first example of mechanochromic acrylic latexes, and it provides insight into the design of force-sensitive and self-reporting polymer coatings.
• We reported the CO2-breathing induced reversible activation of SP3 mechanophore within microgels. This work provides an effective approach to study the forces inside swollen microgels. It also demonstrates the biomimetic processes with shape deformation and concomitant color/fluorescence change. / Thesis / Doctor of Philosophy (PhD) / Smart polymer has been a research focus for recent decades. One of the most critical responses is to monitor mechanical failures of structural materials, such as stress fraction, fatigue and hysteresis within the polymer by giving off early warnings to prevent the catastrophic failure from occurring. The most prevalent approaches to design a mechanoresponsive polymer is to incorporate a “mechanophore”, containing mechanically labile bonds that are subjective to change under exogenous forces. Spiropyrans (SP) are great candidates for stress/strain sensing in terms of mechanochromism. When mechanical force is applied onto Cspiro-O bond, SP undergoes reversible 6-π ring opening reaction to yield merocyanine (MC). The ring-closed form SP is colorless or yellow and nonfluorescent, whereas the ring-open form MC is purple or blue or red and fluorescent. In this project we first designed and synthesized divinyl spiropyran cross-linker, fitting for chain growth polymerization, which accounts for more than 80% of polymer products. Then the divinyl spiropyran cross-linker was covalently incorporated into polymethylacrylate, polyolefins, acrylic latex coating and CO2-breathing microgels, aiming to broaden the potential applications of mechanophore into various polymers. We also summarized the recent development and studies of spiropyran mechanophore into a comprehensive review from an engineering prospective to provide insights into polymer mechanochemistry and study approaches for other mechanophores.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22391 |
| Date | January 2017 |
| Creators | Li, MENG |
| Contributors | Zhu, Shiping, Chemical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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