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. 2015 Aug 25;48(16):5481-5486.
doi: 10.1021/acs.macromol.5b01463. Epub 2015 Aug 7.

Poly(thioester) by Organocatalytic Ring-Opening Polymerization

Timothy J Bannin  1 , Matthew K Kiesewetter  1
Affiliations

Poly(thioester) by Organocatalytic Ring-Opening Polymerization

Timothy J Bannin et al. Macromolecules. .

Abstract

Organocatalysts typically used for the ring-opening polymerization (ROP) of cyclic ester monomers are applied to a thiolactone, ε-thiocaprolactone (tCL). In the absence of an H-bond donor, a nucleophilic polymerization mechanism is proposed. Despite the decreased ability of thioesters and thiols (versus esters and alcohols) to H-bond, H-bonding organocatalysts-a thiourea in combination with an H-bond accepting base-are also effective for the ROP of tCL. The increased nucleophilicity of thiols (versus alcohols) is implicated in the increased Mw/Mn of the poly(thiocaprolactone) versus poly(caprolactone), but deleterious transesterification is suppressed in the presence of a thiourea. The thioester monomer, tCL, is shown to be thermodynamically similar to ε-caprolactam but kinetically similar to ε-caprolactone.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Evolution of percent conversion vs Mn and Mw/Mn for the ROP of tCL (1M) from octadecylthiol (0.02 M) in chloroform catalyzed by (upper) 0.05 M MTBD; and (lower) 0.05 M MTBD and 0.05 M 1. Conversion determined by NMR.
Scheme 1
Scheme 1
Nucleophilic Mechanism for the ROP of tCL with DBU
Scheme 2
Scheme 2
Proposed Bifunctional Mechanism for the ROP of tCL by BEMP/1 Cocatalysts
See this image and copyright information in PMC

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