Colloidal templating: seeded emulsion polymerization of a soluble shell with a controlled alkyne surface density

Abstract

A general methodology for producing ca. 100 nm core–shell colloidal particles in which the shell has an elevated alkyne functionality and yet remains thermoplastic is presented. The availability of accessible alkyne groups on the surface of the aqueous-phase particles allows for the in situ surface modification of the particles through a copper(I) catalyzed Huisgen 1,3-dipolar cycloaddition with an azide-terminated surface agent. The core is an extensively crosslinked polymer which can be easily removed by dispersing the particles in a solvent and centrifuging and collecting the cores, leaving the solubilized shells. This allows for the complete characterization of the colloidal surface reactions in the absence of the volumetrically dominant core. The technique is demonstrated with a core–shell colloid composed of a 135 nm crosslinked polystyrene (PS) core coated with a ca. 10 nm thick uncrosslinked poly(methyl acrylate-co-propargyl acrylate) shell. Due to the applicability of this technique for generating particles useful in biomedical imaging or drug delivery applications, the core–shell particles are surface modified with a variety of azide-terminated poly(ethylene glycol) (PEG) derivatives, including a poloxamer which was terminated on either end by an azide and a naphthalimide chromophore. The resulting fluorescent particles had an absorbance at 413 nm and peak emission at 525 nm. The PEG derivatives could be attached to the particles at a grafting density of ca. 0.2–0.3 groups/nm2.