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Green Polymer Chemistry: Investigating the Mechanism of Radical Ring-Opening Redox Polymerization (R3P) of 3,6-Dioxa-1,8-octanedithiol (DODT)

Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH 44325, USA
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Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Academic Editor: Atsushi Sudo
Molecules 2015, 20(4), 6504-6519; https://doi.org/10.3390/molecules20046504
Received: 28 February 2015 / Revised: 1 April 2015 / Accepted: 7 April 2015 / Published: 13 April 2015
(This article belongs to the Special Issue Ring-Opening Polymerization)
The mechanism of the new Radical Ring-opening Redox Polymerization (R3P) of 3,6-dioxa-1,8-octanedithiol (DODT) by triethylamine (TEA) and dilute H2O2 was investigated. Scouting studies showed that the formation of high molecular weight polymers required a 1:2 molar ratio of DODT to TEA and of DODT to H2O2. Further investigation into the chemical composition of the organic and aqueous phases by 1H-NMR spectroscopy and mass spectrometry demonstrated that DODT is ionized by two TEA molecules (one for each thiol group) and thus transferred into the aqueous phase. The organic phase was found to have cyclic disulfide dimers, trimers and tetramers. Dissolving DODT and TEA in water before the addition of H2O2 yielded a polymer with Mn = 55,000 g/mol, in comparison with Mn = 92,000 g/mol when aqueous H2O2 was added to a DODT/TEA mixture. After polymer removal, MALDI-ToF MS analysis of the residual reaction mixtures showed only cyclic oligomers remaining. Below the LCST for TEA in water, 18.7 °C, the system yielded a stable emulsion, and only cyclic oligomers were found. Below DODT/TEA and H2O2 1:2 molar ratio mostly linear oligomers were formed, with <20% cyclic oligomers. The findings support the proposed mechanism of R3P. View Full-Text
Keywords: disulfide; poly(disulfide)s; thiol oxidation; radical polymerization; ring polymers; cyclic polymers; oxidation-reduction; reducible polymers disulfide; poly(disulfide)s; thiol oxidation; radical polymerization; ring polymers; cyclic polymers; oxidation-reduction; reducible polymers
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Rosenthal-Kim, E.Q.; Puskas, J.E. Green Polymer Chemistry: Investigating the Mechanism of Radical Ring-Opening Redox Polymerization (R3P) of 3,6-Dioxa-1,8-octanedithiol (DODT). Molecules 2015, 20, 6504-6519.

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