Thiol-functionalized branched and linear poly(ε-caprolactone): Direct synthesis, characterization and application in stabilizing silver nanoparticles

Yttrium trisphenolates was developed as highly chemoselective catalyst toward thiol, primary and secondary hydroxyl. By utilizing yttrium trisphenolates, well-defined thiol-functionalized branched and linear poly(ε-caprolactone) were directly synthesized via ring-opening polymerization of ε-caprolactone in the presence of unprotected 3-mercaptopropane-1, 2-diol and 2-mercapto-1-ethanol as initiator respectively. The expected structures were characterized by ¹H NMR, MALDI TOF MS and SEC. High thiol fidelities (>70%) and yields (>90%) of products were obtained with controlled molecular weights. The resultant thiol-functionalized poly(ε-caprolactone) were used to stabilize silver nanoparticles through two-phase method. The red shift of the UV-vis absorption band of linear poly(ε-caprolactone) protected nanoparticles was observed comparing with the branched counterpart. Both two kinds of nanoparticles were well-dispersed with diameters around 2-3 nm according to TEM.