Synthesis and Characterization of Poly(ε-caprolactone-b-4-vinylpyridine): Initiation, Polymerization, Solution Morphology, and Gold Metalation

Abstract

We have synthesized a difunctional initiator—the hydroxyl-4-oxo-N-alkoxyamine (HOA)—by first mixing benzoyl peroxide (BPO) and 4-hydroxyl-2,2,6,6-tetramethylpiperdinooxy (4-OH-TEMPO) in styrene at temperatures below 25 °C to give the 4-oxo-N-alkoxyamine (OA) and then hydrolyzing the benzoate ester on OA with NaOH. This low-temperature preparation of OA reveals that benzyloxyl radicals can be generated from the BPO through redox reaction with 4-OH-TEMPO as well as through thermal decomposition. The N-oxoammonium cation (i.e., the oxidative state of 4-OH-TEMPO), which formed as a side product, mediated the alcohol oxidation to give OA. We prepared three PCL-b-P4VP diblock copolymers (BC1−3) from HOA through two-step polymerizations: (i) diethylaluminum alkoxide-induced ring-opening polymerization of ε-caprolactone at 25 °C followed by (ii) nitroxide-mediated radical polymerization of 4-vinylpyridine at 125 °C. With the combination of biodegradable hydrophobic PCL blocks and polymeric blocks of P4VP ligands, we used the immiscible PCL-b-P4VP copolymers to transport AuCl4− anions from aqueous phases to organic phases and to stabilize Au nanoparticles in the PCL-b-P4VP micelles Au-BC1−3 after reduction with NaBH4.