Two general methods for the synthesis of thiol-functional polycaprolactones

We report here two different methods for preparing thiol-functional polymers. The first method consists of esterifying the hydroxyl-terminated polyesters with a thiol-protected mercaptoacetic acid. The Sangers reagent (2,4-dinitrofluorobenzene) was used to protect the mercaptoacetic acid and was removed with mercaptoethanol under mild conditions. The second technique involves the preparation of a protected thiol-functional initiator, the alpha-(2,4-dinitrophenylthio)ethanol, that could then be used in the polymerization of epsilon-caprolactone. This "functionalization from initiation" technique could also lead to the preparation of well-defined multibranched polymers with a thiol group at the focal point after the polymerization with a mercapto-initiator carrying dihydroxy or tetrahydroxy functionalities as initiating sites. The ultimate motivation in the preparation of such functional polymers is to elaborate nanocomposites by using the polymers as macroligands in the synthesis of nanoparticles.