Polystyrene Colloids with Surface-Grafted Polyethylene Oxide as Model Systems for Site-Specific Drug Delivery: I. Preparation and Surface Chemical Characterization Using SIMS and XPS

Abstract

A range of copolymer colloids with covalently attached polyethylene oxide (PEO) (2000 Da) chains have been prepared by potassium persulfate-initiated emulsion copolymerization of styrene with a PEO acrylate macromonomer. The surface orientation of the macromonomer chains has been confirmed by the combined use of static secondary ion mass spectrometry (SSIMS) and X-ray photoelectron spectroscopy (XPS). The surface analysis data proved entirely complementary. The detection of molecular ions diagnostic of PEG within the SSIMS spectra and their increase in relative intensity with increasing macromonomer content provided clear evidence of the surface presence of PEO for the range of polystyrene (PS)-PEO colloids. Similarly, the XPS studies showed that the level of PEO, as inferred from the ether C-O carbon environment within the C1s spectra, increased with increasing levels of macromonomer in the latex. This surface analytical data on these near-monodispersed colloids was complemented by particle size, electrophoretic mobility, and colloid stability analysis, all of which showed a marked dependence on the level of surface PEO. The relevance of these findings is discussed both in terms of the particle formation mechanism and in the context of the potential of these colloids as model systems for probing the influence of PEO surface density on colloidal biodistribution in vivo.