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In situ EPR and Raman spectroscopy in the curing of bis-methacrylate–styrene resins

The curing of bis-methacrylate–styrene resins initiated by the cobalt catalyzed decomposition of cumyl hydroperoxide is monitored at ambient temperatures in situ by EPR and Raman spectroscopy. EPR spectroscopy shows the appearance of organic radicals after ca. 1 h from initiation with an increase in...

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Autores principales: Eijsink, Linda E., Sardjan, Andy S., Sinnema, Esther G., den Besten, Hugo, van den Berg, Keimpe J., Flapper, Jitte, van Gemert, Rogier, Feringa, Ben L., Browne, Wesley R.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: The Royal Society of Chemistry 2022
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8979059/
https://www.ncbi.nlm.nih.gov/pubmed/35425317
http://dx.doi.org/10.1039/d1ra09386j
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author Eijsink, Linda E.
Sardjan, Andy S.
Sinnema, Esther G.
den Besten, Hugo
van den Berg, Keimpe J.
Flapper, Jitte
van Gemert, Rogier
Feringa, Ben L.
Browne, Wesley R.
author_facet Eijsink, Linda E.
Sardjan, Andy S.
Sinnema, Esther G.
den Besten, Hugo
van den Berg, Keimpe J.
Flapper, Jitte
van Gemert, Rogier
Feringa, Ben L.
Browne, Wesley R.
author_sort Eijsink, Linda E.
collection PubMed
description The curing of bis-methacrylate–styrene resins initiated by the cobalt catalyzed decomposition of cumyl hydroperoxide is monitored at ambient temperatures in situ by EPR and Raman spectroscopy. EPR spectroscopy shows the appearance of organic radicals after ca. 1 h from initiation with an increase in intensity from both polystyrene and methacrylate based radical species over a further ca. 2 h period to reach a maximum spin concentration of ca. 2–3 mM. Alkene conversion to polymer was monitored by Raman spectroscopy in real time in situ with EPR spectroscopy and reveals that the appearance of the radical signals is first observed only as the conversion approaches its maximum extent (70% at room temperature), i.e., the resin reaches a glass-like state. The radicals persist for several months on standing at room temperature. Flash frozen samples (77 K) did not show EPR signals within 1 h of initiation. The nature of the radicals responsible for the EPR spectra observed were explored by DFT methods and isotope labelling experiments (D(8)–styrene) and correspond to radicals of both methacrylate and polystyrene. Combined temperature dependent EPR and Raman spectroscopy shows that conversion increases rapidly upon heating of a cured sample, reaching full conversion at 80 °C with initially little effect on the EPR spectrum. Over time (i.e. subsequent to reaching full conversion of alkene) there was a small but clear increase in the EPR signal due to the methacrylate based radicals and minor decrease in the signal due to the polystyrene based radicals. The appearance of the radical signals as the reaction reaches completion and their absence in samples flash frozen before polymerization has halted, indicate that the observed radicals are non-propagating. The formation of the radicals due to stress within the samples is excluded. Hence, the observed radicals are a representative of the steady state concentration of radicals present in the resin over the entire timespan of the polymerization. The data indicate that the lack of EPR signals is most likely due to experimental aspects, in particular spin saturation, rather than low steady state concentrations of propagating radicals during polymerization.
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spelling pubmed-89790592022-04-13 In situ EPR and Raman spectroscopy in the curing of bis-methacrylate–styrene resins Eijsink, Linda E. Sardjan, Andy S. Sinnema, Esther G. den Besten, Hugo van den Berg, Keimpe J. Flapper, Jitte van Gemert, Rogier Feringa, Ben L. Browne, Wesley R. RSC Adv Chemistry The curing of bis-methacrylate–styrene resins initiated by the cobalt catalyzed decomposition of cumyl hydroperoxide is monitored at ambient temperatures in situ by EPR and Raman spectroscopy. EPR spectroscopy shows the appearance of organic radicals after ca. 1 h from initiation with an increase in intensity from both polystyrene and methacrylate based radical species over a further ca. 2 h period to reach a maximum spin concentration of ca. 2–3 mM. Alkene conversion to polymer was monitored by Raman spectroscopy in real time in situ with EPR spectroscopy and reveals that the appearance of the radical signals is first observed only as the conversion approaches its maximum extent (70% at room temperature), i.e., the resin reaches a glass-like state. The radicals persist for several months on standing at room temperature. Flash frozen samples (77 K) did not show EPR signals within 1 h of initiation. The nature of the radicals responsible for the EPR spectra observed were explored by DFT methods and isotope labelling experiments (D(8)–styrene) and correspond to radicals of both methacrylate and polystyrene. Combined temperature dependent EPR and Raman spectroscopy shows that conversion increases rapidly upon heating of a cured sample, reaching full conversion at 80 °C with initially little effect on the EPR spectrum. Over time (i.e. subsequent to reaching full conversion of alkene) there was a small but clear increase in the EPR signal due to the methacrylate based radicals and minor decrease in the signal due to the polystyrene based radicals. The appearance of the radical signals as the reaction reaches completion and their absence in samples flash frozen before polymerization has halted, indicate that the observed radicals are non-propagating. The formation of the radicals due to stress within the samples is excluded. Hence, the observed radicals are a representative of the steady state concentration of radicals present in the resin over the entire timespan of the polymerization. The data indicate that the lack of EPR signals is most likely due to experimental aspects, in particular spin saturation, rather than low steady state concentrations of propagating radicals during polymerization. The Royal Society of Chemistry 2022-01-19 /pmc/articles/PMC8979059/ /pubmed/35425317 http://dx.doi.org/10.1039/d1ra09386j Text en This journal is © The Royal Society of Chemistry https://creativecommons.org/licenses/by-nc/3.0/
spellingShingle Chemistry
Eijsink, Linda E.
Sardjan, Andy S.
Sinnema, Esther G.
den Besten, Hugo
van den Berg, Keimpe J.
Flapper, Jitte
van Gemert, Rogier
Feringa, Ben L.
Browne, Wesley R.
In situ EPR and Raman spectroscopy in the curing of bis-methacrylate–styrene resins
title In situ EPR and Raman spectroscopy in the curing of bis-methacrylate–styrene resins
title_full In situ EPR and Raman spectroscopy in the curing of bis-methacrylate–styrene resins
title_fullStr In situ EPR and Raman spectroscopy in the curing of bis-methacrylate–styrene resins
title_full_unstemmed In situ EPR and Raman spectroscopy in the curing of bis-methacrylate–styrene resins
title_short In situ EPR and Raman spectroscopy in the curing of bis-methacrylate–styrene resins
title_sort in situ epr and raman spectroscopy in the curing of bis-methacrylate–styrene resins
topic Chemistry
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8979059/
https://www.ncbi.nlm.nih.gov/pubmed/35425317
http://dx.doi.org/10.1039/d1ra09386j
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