Photoresponsive thiourea and urea catalysts for ring-opening polymerization of L-lactide

Stimulus responsive catalysts have received increasing attention. Photoresponsive catalytic polymerization is particularly attractive because the noninvasive and versatile nature of light. Most photoresponsive ROP catalytic systems exhibit low activities, allowing ROP to be completed within several hours to 10 h. In this contribution, a series of (thio)ureas bearing dithienylcyclopentene optical molecular switch moiety are designed, synthesized, and characterized. The photoresponsive effects in (thio)urea/alkoxide mediated ROP of L-lactide are investigated. These catalysts allow the ROP reactions of L-lactide to be completed within a few minutes to 1 h and the resulting polyesters have narrow molecular weight distributions. The dithienylcyclopentene moiety allows photoisomerization to be completed within 1 min. The catalytic activity of the ROP catalyst can be altered by the photoisomerization of the dithienyl cyclopentene moiety by exposure to ultraviolet or visible light, respectively.