Surface characterization of blood compatible amphiphilic graft copolymers having uniform poly(ethylene oxide) side chains

The surface characterization of poly(methyl methacrylate)-graft-poly(ethylene oxide) (PMMA-g-PEO) was investigated by XPS and contact-angle measurement, and its in vitro blood compatibility was assessed by plasma recalcification time measurement. The surface and bulk composition of different PMMA-g-PEO graft copolymer showed that PMMA segments were always enriched at the copolymer–air interface, but surface enrichment of PEO segments could occur in films of copolymers with longer PEO side chain (Mn of PEO, 3200) and a higher bulk PEO content. Contact-angle studies indicated that the surface hydrophilicity increased as the surface PEO content increased. The contact angles of water on the copolymer decreased linearly with contact time until they reached a balance value θe or 0, and the relationship between θ (from the static contact angle, θs to θe) and contact time(t) can be expressed by: θ=−kt. The proportionality constant k and Δθ (θs−θe) depended on the bulk structural parameters (the bulk composition and PEO side chain length). The microphase-separated structure of copolymers was also observed by transmission electron microscopy (TEM). The relationship between the surface properties of PMMA-g-PEO graft copolymer and its blood compatibility was addressed.