Alkyne Functional Block Copolymers as Precursors to Cobalt Nanoparticles

Abstract

Block copolymers are those that contain two or more homopolymer units connected together on a single chain. They are of great interest for their ability to phase-separate and form highly ordered structures on the nanometer scale. Amphiphilic block copolymers contain hydrophobic and hydrophilic blocks which allow them to self-assemble in aqueous solution, which has potential for various medical applications. Functionalized block copolymers also have potential to form metal-polymer hybrid materials that can self-assemble and form highly-ordered nanostructures, which may be useful for technological applications. In this work, alkyne-functional block copolymers were synthesized and used to create cobalt-copolymer composites. ABA triblock copolymer poly[4-(phenylethynyl)styrene]-b-poly(ethylene oxide)-b-poly[4-(phenylethynyl)styrene] was synthesized at a variety of molecular weights by atom transfer radical polymerization (ATRP) of 4-PES onto a difunctional poly(ethylene oxide) macroinitiator (PEO, M_n=~10,000 g/mol). AB diblock copolymers poly(ethylene oxide)-b-poly[4-(phenylethynyl)styrene] and polystyrene-b-poly[4-(phenylethynyl)styrene] were synthesized at a variety of molecular weights by ATRP of 4-PES onto monofunctional PEO and polystyrene (PS) macroinitiators (PEO M_n=~5,000 g/mol; PS M_n=~4400 g/mol). Copolymer products were analyzed by <super>1</super>H NMR spectroscopy and gel permeation chromatography (GPC). Polydispersities of diblock copolymers were fairly narrow (1.10-1.25), indicating well controlled polymerizations. Copolymer samples were treated with Co₂(CO)₈ in solution to form cobalt-functional block copolymers. Transmission electron microscopy was used to investigate the structural properties of the cobalt composite of triblock copolymer PPES₅₅-PEO₂₂₇-PPES₅₅, and showed spherical structures 15-40 nm in diameter.