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. 2018 May 23;10(6):577. doi: 10.3390/polym10060577

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© 2018 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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Scheme 1 — Ring-expansion polymerization (REP) of ε-caprolactone (CL): (a) 2,2-dibutyl-2-stanna-1,3-dioxebutane [n-Bu₂Sn(OCH₂CH₂CH₂CH₂O)] was used as a cyclic initiator [13,14,15,16,17]; (b) alkyl-organoaluminum initiators were used as initiators [18].