Synthesis of poly(ethylene-co-butylene)-block-poly(ethylene oxide) surfactant and its use in the synthesis of polyhydroxyethyl methacrylate nanoparticles containing azo-dye
A synthetic path to poly(ethylene-co-butylene)-block-poly(ethylene oxide), a substitute for the "KLE" surfactant was developed. For this purpose, mono hydroxyl end-functionalized poly(ethylene-co-butylene) (similar to 3800 g mol(-1)) was modified with a triple bond at its hydroxyl group, while two samples of mono hydroxyl end-functionalized poly(ethylene oxide) (similar to 2000 g mol(-1) and 5000 g mol(-1)) were modified with an azide group. The two blocks were bound together by click chemistry and the products characterized by 1H NMR spectroscopy, EA and GPC. The ability of these new block copolymers to stabilize nanodroplets in inverse miniemulsion polymerization of 2-hydroxyethyl methacrylate (HEMA) was investigated. It was found that the molecular weight of the poly(ethylene oxide) block strongly influences the stability of the miniemulsions; only the copolymer with the short oligoethylene block gave satisfactory results. The possibility of encapsulating Disperse Red 1 (DR1) dye in polyhydroxyethyl methacrylate (PHEMA) was also investigated and the miniemulsions were optimized such as to prepare particles with a maximum DR1 loading of approximately 21 wt%. To avoid dye agglomeration and phase separation during polymerization, DR1 was equipped with a polymerizable group. The resulting particles were characterized by DLS, SEM, TGA, UV-vis and DSC. These particles are of importance as fillers in polydimethylsiloxane composites that are used as electrostrictive materials.