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Authors
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Metzler, L. ; Reichenbach, T. ; Brügner, O. ; Komber, H. ; Lombeck, F. ; Müllers, S. ; Hanselmann, R. ; Hillebrecht, T. ; Walter, M. ; Sommer, M.
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Title
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High molecular weight mechanochromic spiropyran main chain copolymers via reproducible microwave-assisted suzuki polycondensation
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Date
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09.04.2015
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Number
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46043
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Abstract
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Suzuki-Miyaura polycondensation (SPC) is widely used to prepare of a variety of copolymers for a broad range of applications. Despite SPC protocols are often used in many instances, the limits of this method and issues of molecular weight reproducibility are not often looked at into detail. By using a spiropyran-based (SP) mechanochromic copolymer, we present an optimized protocol for the microwave-assisted SPC of a mechanochromic, alternating copolymer P(SP-alt-C10) that allows to reproduce molecular weight distributions. Several parameters such as microwave power, temperature, stoichiometry, and ligand are screened, leading to molecular weights up to Mw ~ 174 kg/mol. The process of optimization is guided by NMR end group analysis which shows that dehalogenation, oxidative deborylation and SP cleavage are the limiting factors that impede further increase of molar masses, while other classical side reactions such as protiodeborylation are not observed. Embossing films of P(SP-alt-C10) yields the colored merocyanine (MC) copolymer P(MC-alt-C10) that undergoes a thermally facilitated back reaction to P(SP-alt-C10). DFT suggests that the barrier of the SP to MC transition has two contributions, with the first one being related to the color change and the second one to internal bond reorganizations. The barrier height is 1.5 eV, which suggests that the ease of the thermally facilitated back reaction is either due to residual energy stored in the deformed polymer matrix, or arises from an MC isomer that is not in the thermodynamically most stable state.
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Publisher
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Polymer Chemistry
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Wikidata
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Citation
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Polymer Chemistry 6 (2015) 3694-3707
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DOI
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https://doi.org/10.1039/C5PY00141B
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Tags
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