Gold Nanoparticles Protected with Thiol-Derivatized Amphiphilic Poly(ϵ-caprolactone)-b-poly(acrylic acid)

Amphiphilic poly(ϵ-caprolactone)-b-poly(acrylic acid) (HS-PCL-b-PAA) with a thiol functionality in the PCL terminal has been prepared in a novel synthetic cascade. Initially, living anionic ring-opening polymerization (ROP) of ϵ-caprolactone (ϵ-CL) employing the difunctional initiator, 2-hydroxyethyl 2-bromoisobutyrate, followed by esterification with 2,4-dinitrophenyl- or 4-monomethoxytrityl-protected mercaptoacetic acids (Prot-), provided well-defined PCL macroinitiators capped with protected thiols.

The macroinitiators allowed atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBA) in a controlled fashion by use of NiBr2(PPh3)2 catalyst to produce Prot-PCL-b-PtBA with narrow polydispersities (1.17−1.39). Subsequent mild deprotection protocols provided HS-PCL-b-PAA. Reduction of a gold salt in the presence of this macroligand under thiol-deficient conditions afforded stable, aggregation-free nanoparticles, as evidenced from UV−vis spectroscopy and transmission electron microscopy (TEM), the latter revealed nanoparticles with a mean diameter of 9.0 ± 3.1 nm.