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

S. Naumann, A.W. Thomas, A.P. Dove

Research output: Contribution to journalArticlepeer-review

65 Citations (Scopus)


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.
Original languageEnglish
Pages (from-to)134–138
JournalACS Macro Letters
Issue number1
Publication statusPublished - 6 Jan 2016


  • N-heterocyclic olefins
  • olefins
  • organopolymerization
  • metal-free polymerization
  • Lactones
  • trimethylene carbonate
  • methyl substituents
  • ring-opening polymerization


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