Poly(thioester) by Organocatalytic Ring-Opening Polymerization

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 <i>M</i>_w/<i>M</i>_n 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