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Cited by 97biodegradable polymer synthesis and propertiesCarbon dioxide utilization in catalysisAdvanced Polymer Synthesis and Characterization

Highly Polarized Alkenes as Organocatalysts for the Polymerization of Lactones and Trimethylene Carbonate

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Naumann, Stefan, Thomas, Anthony W., Dove, Andrew P.·2016·ACS Macro Letters
DOI 10.1021/acsmacrolett.5b00873
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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.

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  • Under the same conditions, the ROP of VL is fast but poorly controlled due to the more significant enolate-based initiation.

    “Under the same conditions, the ROP of VL is fast but poorly controlled due to the more significant enolate-based initiation.”

    From Catalysis as an Enabling Science for Sustainable Polymers (2018) · cites this paper as [334]

  • N-heterocyclic olefins have emerged as a class of active and versatile catalysts for the ROP of cyclic esters and carbonates.

    “Recently, N-heterocyclic olefins (NHOs) have emerged as a class of active and versatile catalysts for the ROP of cyclic esters and carbonates.334,335”

    From Catalysis as an Enabling Science for Sustainable Polymers (2018) · cites this paper as [334]

  • In the presence of an alcohol initiator, the ROP of 50 equiv L-LA by as low as 0.2 mol% NHO-2 reached quantitative conversion in less than a minute, resulting in PLAs with low molecular weight distributions (Ð < 1.2).

    “In the presence of an alcohol initiator, the ROP of 50 equiv.L-LA by as low as 0.2 mol% NHO-2 reached quantitative conversion in less than a minute, resulting in PLAs with low molecular weight distributions (Ð <1.2).”

    From Catalysis as an Enabling Science for Sustainable Polymers (2018) · cites this paper as [334]

  • While non-substituted NHOs were ineffective for ROP due to catalyst deactivation, NHO bearing dimethyl substituents proved highly active for the ROP of LA and VL.

    “While non-substituted NHOs (at the exocyclic carbon, NHO-1,3) were ineffective for ROP due to catalyst deactivation (Scheme 11C), NHO bearing dimethyl substituents (NHO-2) proved highly active for the ROP of LA and VL.334”

    From Catalysis as an Enabling Science for Sustainable Polymers (2018) · cites this paper as [334]

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Research works printed but not linked: 31

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Authors
Naumann, S., Thomas, A. W., & Dove, A. P.
Affiliations
University of Warwick (GB)
Corresponding author
  • Naumann, Stefan
  • Dove, Andrew P.
ORCID
Venue
ACS Macro Letters
Publisher
American Chemical Society (ACS)
Published
2016-01-06
Volume
5
Issue
1
Pages
134-138
ISSN
2161-1653 (ISSN-L)
DOI
10.1021/acsmacrolett.5b00873
OpenAlex
W2227905365
Cited by
97
References
32
Citations by year
2026: 6 · 2025: 7 · 2024: 3 · 2023: 2 · 2022: 8 · 2021: 7 · 2020: 8 · 2019: 14 · 2018: 17 · 2017: 12 · 2016: 12
FWCI
7.50
Type
journal article
Language
en
Open access
Licence
Locations
  • ACS Macro Letters (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Warwick Research Archive Portal (University of Warwick) (acceptedVersion)
  • University of Birmingham Research Portal (University of Birmingham) (submittedVersion)
Funders
Deutsche Forschungsgemeinschaft (NA 1206)
Topics
  • Physical Sciences › Materials Science › Biomaterials › biodegradable polymer synthesis and properties
  • Physical Sciences › Chemical Engineering › Process Chemistry and Technology › Carbon dioxide utilization in catalysis
  • Physical Sciences › Chemistry › Organic Chemistry › Advanced Polymer Synthesis and Characterization
Keywords
N-heterocyclic olefins, organocatalysis, ring-opening polymerization, lactones, trimethylene carbonate, L-lactide, δ-valerolactone, ε-caprolactone, structure-activity relationship, catalyst basicity, polymerization control, polymerization pathways, metal-free polymerization

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