Polymer Microspheres with Permanent Antibacterial Surface from Surface-Initiated Atom Transfer Radical Polymerization

Cross-linked poly(4-vinylbenzyl chloride) (PVBC) microspheres were first synthesized by suspension copolymerization of 4-vinylbenzyl chloride (VBC) in the presence of a cross-linking agent, ethylene glycol dimethacrylate (EGDMA). Subsequent modification of the microsphere surfaces via surface-initiated atom transfer radical polymerization (ATRP) of 2-(dimethylamino)ethyl methacrylate (DMAEMA), using the VBC units of PVBC on the microsphere surface as the macroinitiators, gave rise to well-defined (nearly monodisperse) and covalently tethered poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) brushes. Quaternization of the tertiary amine groups of the PDMAEMA brushes with alkyl bromides (1-bromododecane or 1-bromohexane) gave rise to a high concentration of quaternary ammonium salt (QAS) on the microsphere surfaces. The chemical composition of the microsphere surfaces at various stages of surface modification was characterized by X-ray photoelectron spectroscopy (XPS). The bactericidal effect of the QAS-functionalized microspheres on Escherichia coli and Staphylococcus aureus was demonstrated. The permanence of the bactericidal activity was also demonstrated through the repeated applications of the surface-modified PVBC microspheres without any significant loss of their surface activity or functionality.