Zwitterionic polymer-grafted microspheres prepared by RAFT polymerization

Using a macro-RAFT agent composed of zwitterionic poly(carboxymethyl betaine) (PCMB), butyl acrylate was polymerized in emulsion polymerization system to give microspheres (PCMB-MS). Microspheres having cationic or anionic graft chains were also prepared using the similar procedures. The dispersion of PCMB-MS was very stable, and the addition of neither sodium chloride nor proteins affected colloidal properties of the MS at all. In contrast, significant salt- and protein-induced aggregations of the lopsidedly charged microspheres were observed. Upon deionization, furthermore, the dispersion of anionic poly(methacrylic acid)-grafted-MS (PMA-MS) showed clear iridescence, and its peak reflectivity was more than 90 % due to the formation of colloid crystal driven by both the electrostatic and steric repulsions between the MSs. The dispersion of PCMB-MS also showed iridescence, though its reflectivity (< 60 %) was smaller than that of PMA-MS probably because of the smaller electrostatic repulsion between PCMB-MSs than that between PMA-MSs.