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Highly polarized alkenes as organocatalysts for the polymerization of lactones and trimethylene carbonate
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Naumann, Stefan, Thomas, Anthony W. and Dove, Andrew P. (2016) Highly polarized alkenes as organocatalysts for the polymerization of lactones and trimethylene carbonate. ACS Macro Letters, 5 (1). pp. 134-138. 5b00873. doi:10.1021/acsmacrolett.5b00873 ISSN 2161-1653.
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Official URL: http://dx.doi.org/10.1021/acsmacrolett.5b00873
Abstract
In this work, the activity of N-heterocyclic olefins
(NHOs), a newly emerging class of organopolymerization catalyst, is investigated to affect the metal-free polymerization of lactones and trimethylene carbonate (TMC). A decisive structure−activity relationship is revealed. While catalysts of the simplest type bearing an exocyclic CH2 moiety polymerize L-lactide (L-LA) and δ-valerolactone (δ-VL) in a non-living and non-quantitative manner, the introduction of methyl substituents on the exocyclic carbon radically changes this behavior. 2-Isopropylidene-1,3,4,5-tetramethylimidazoline is found to be highly active for a range of monomers such as L-LA, δ-VL, ε-caprolactone (ε-CL), and TMC, with quantitative conversion occurring within seconds with catalyst loadings of just 0.2 mol %. The high activity of this NHO further enables the ring-opening polymerization (ROP) of the macrolactone ω-pentadecalactone (PDL). However, this broad applicability is offset by a lack of control over the polymerizations, including side reactions as a consequence of its strong basicity. To overcome this, a saturated, imidazolinium-derived analogue was synthesized and subsequently demonstrated to possess a harnessed reactivity which enables it to polymerize both L-LA and TMC in a controlled manner (ĐM < 1.2). NMR spectroscopic and MALDI-ToF MS experiments highlight the differences in polymerization pathways for 2-methylene-1,3,4,5-tetramethylimidazoline, in which the exocyclic carbon is not substituted, in contrast to 2-isopropylidene-1,3,4,5-tetramethylimidazoline, with the former operating
via its nucleophilicity and the latter acting as a base with enolizable δ-VL.
Item Type: | Journal Article | ||||||||
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Subjects: | Q Science > QD Chemistry | ||||||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Chemistry | ||||||||
Library of Congress Subject Headings (LCSH): | Chemistry, Organic, Catalysis, Asymmetric synthesis | ||||||||
Journal or Publication Title: | ACS Macro Letters | ||||||||
Publisher: | American Chemical Society | ||||||||
ISSN: | 2161-1653 | ||||||||
Official Date: | 6 January 2016 | ||||||||
Dates: |
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Volume: | 5 | ||||||||
Number: | 1 | ||||||||
Page Range: | pp. 134-138 | ||||||||
Article Number: | 5b00873 | ||||||||
DOI: | 10.1021/acsmacrolett.5b00873 | ||||||||
Status: | Peer Reviewed | ||||||||
Publication Status: | Published | ||||||||
Access rights to Published version: | Open Access (Creative Commons) | ||||||||
Funder: | Engineering and Physical Sciences Research Council (EPSRC) |
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