Continuous flow protecting-group-free synthetic approach to thiol-terminated poly(ε-caprolactone)

A novel continuous flow protecting-group-free synthetic approach was developed to thiol-terminated poly(ε-caprolactone). Sn(OTf)2 catalyzed unprotected 6-mercapto-1-hexanol initiating chemoselective ring-opening polymerization of ε-caprolactone was conducted in PTFE tubular reactor. This continuous flow polymerization platform achieved quantitative chemoselectivity and fast polymerization that cannot be done in batch. By changing the [monomer]/[initiator] feed ratio, the molecular weights of products were well controlled with narrow molecular weight distributions. The structure of the resultant thiol-terminated poly(ε-caprolactone) was demonstrated by NMR, MALDI TOF MS and SEC.