Protecting-group-free synthesis of thiol-functionalized degradable polyesters

Thiol-functionalized degradable polyesters have significant applications in nanoscience and polymer chemistry due to the combination of the biodegradability and biocompatibility of polyesters and the special chemical and physical properties of thiols. It is challenging to synthesize thiol-functionalized polyesters via ring-opening polymerization by using unprotected mercapto-alcohol as an initiator because both hydroxyl and thiol have the ability to initiate the polymerization. Since 2005, the protecting-group-free synthetic strategy has been reported based on chemoselective catalysis and microflow technology. In this review, non-metal and metal catalytic unprotected mercapto-alcohol initiating ring-opening polymerization is summarized in order. The advantages of using flow chemistry are highlighted. The remaining challenges and opportunities are discussed for the development of thiol-polymer synthesis and applications.