Ring-opening polymerization of β-thiobutyrolactone catalyzed by phosphazenes

Thiolactones that give access to polythioesters (PTEs) upon ring-opening polymerization (ROP) have recently attracted increasing attention especially due to their biocompatibility and improved degradability among other properties. We report herein on the ROP of the simplest four-membered ring thiola...

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Bibliographic Details
Published in:Polymer chemistry 2023-08, Vol.14 (33), p.3851-3861
Main Authors: Li, Hui, Guillaume, Sophie M, Carpentier, Jean-Franois
Format: Article
Language:English
Subjects:
Basicity
Biocompatibility
Chemical Sciences
Chemical synthesis
Dispersion
Ion pairs
Monomers
NMR
Nuclear magnetic resonance
Phosphazene
Polymer chemistry
Polymerization
Ring opening polymerization
Room temperature
Spectrometry
Steric hindrance
Toluene
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Summary:Thiolactones that give access to polythioesters (PTEs) upon ring-opening polymerization (ROP) have recently attracted increasing attention especially due to their biocompatibility and improved degradability among other properties. We report herein on the ROP of the simplest four-membered ring thiolactone, namely racemic β-thiobutyrolactone ( rac -TBL), mediated by commercially available phosphazene bases, affording the corresponding poly(3-thiobutyrolactone) (P3TB). The reactions proceeded at room temperature, in toluene or in THF, with the apparent reactivity increasing monotonously with the basicity and steric hindrance of the phosphazene (BEMP t Bu-P 1 < t Bu-P 2 < t Bu-P 4 ). This trend suggests that initiation of the ROP proceeds, at least to some extent, by abstraction of one acidic methylene hydrogen from the monomer, to generate eventually a phosphazenium-thiocarboxylate ion-pair species that next acts as the initiating/chain-propagating species. ROP performed in THF was kinetically controlled affording P3TBs with defined molar mass and fair dispersity, some features of a living ROP. Detailed 1 H, 13 C, 31 P and DOSY NMR spectroscopic, MALDI-ToF/ESI mass spectrometric and TGA studies conducted on the polymers produced using t Bu-P 4 supported the concomitant formation of {[ t Bu-P 4 ]H} + and essentially α-thiocrotonate,ω-[thiocarboxylate] − end-capped linear P3TBs; yet, the presence of cyclic P3TBs could not be excluded. The molar mass values, as determined by NMR analysis from this thiocrotonate end-group ( M n,NMR ), increased linearly with the monomer conversion, yet with a nonzero intercept, suggesting slow initiation vs . propagation. The molar mass of the recovered P3TBs was moderately controlled ( M n,SEC = 7.5-18.5 kg mol −1 , M n,NMR = 5.2-22.4 kg mol −1 ), displaying relatively narrow dispersities ( M = 1.39-1.52 in THF). This work provides the second example of chemical synthesis of P3TB. Ring-opening polymerization of β-thiobutyrolactone proceeds effectively in the presence of phosphazenes, especially the more basic ones. Mechanistic issues are discussed in light of spectroscopic, spectrometric and kinetic data.
ISSN:1759-9954
1759-9962
DOI:10.1039/d3py00707c