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Polymers 2018, 10(8), 844; https://doi.org/10.3390/polym10080844

Identity of Low-Molecular-Weight Species Formed in End-To-End Cyclization Reactions Performed in THF

Department of Chemistry and Biochemistry, Santa Clara University, 500 El Camino Real, Santa Clara, CA 95053, USA
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Received: 19 July 2018 / Accepted: 27 July 2018 / Published: 31 July 2018
(This article belongs to the Special Issue Cyclic Polymers)
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Abstract

Cyclic polymers were produced by end-to-end coupling of telechelic linear polymers under dilute conditions in THF, using intramolecular atom transfer radical coupling or click chemistry. In addition to the expected shift to longer elution times on gel permeation chromatography (GPC) indicative of the formation of cyclic product, lower molecular weight species were consistently observed upon analysis of the unpurified cyclization reaction mixture. By systematically removing or altering single reaction components in the highly dilute cyclization reaction, it was found that THF itself was responsible for the low-molecular-weight material, forming oligomeric chains of poly(THF) regardless of the other reaction components. When the reactions were performed at higher concentrations and for shorter time intervals, conducive to intermolecular chain-end-joining reactions, the low-molecular-weight peaks were absent. Isolation of the material and analysis by 1H NMR confirmed that poly(THF) was being formed in the highly dilute conditions required for cyclization by end-to-end coupling. When a series of mock cyclization reactions were performed with molar ratios of the reactants held constant, but concentrations changed, it was found that lower concentrations of reactants led to higher amounts of poly(THF) side product. View Full-Text
Keywords: cyclic polymers; click chemistry; atom transfer radical coupling cyclic polymers; click chemistry; atom transfer radical coupling
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Pan, C.W.; Xia, K.; Parker, S.A.; Tillman, E.S. Identity of Low-Molecular-Weight Species Formed in End-To-End Cyclization Reactions Performed in THF. Polymers 2018, 10, 844.

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