Preparation of highly monodisperse fluorescent polymer particles by miniemulsion polymerization of styrene with a polymerizable surfactant

Abstract

Miniemulsion polymerization of styrene (St) in the presence of a hydrophobe (hexadecane:HD) using a cationic polymerizable surfactant ( N , N -dimethyl- N - n -dodecyl- N-2-methacryloyloxyethylammonium bromide:C 12Br) and a cationic initiator (2,2′-azobis(2-amidinopropane) dihydrochloride:V50), called St/C 12Br/V50 hereafter, proceeded efficiently compared with that using sodium dodecyl sulfate (SDS) and potassium persulfate (KPS), i.e., St/SDS/KPS, providing monodisperse polystyrene latex particles with a narrower particle size distribution. In St/C 12Br/AIBN, where an oil-soluble initiator, i.e., 2,2′-azobisisobutyronitrile (AIBN), was used in place of V50, little changes in polymerization kinetics or in particle size distribution were observed, while a significant drop in polymerization rate and a broad particle size distribution were observed with St/SDS/AIBN. A polymerizable pyrene derivative (1-pyrenylmethyl methacrylate: PyMMA) was quantitatively incorporated into monodisperse latex particles in St/PyMMA/C 12Br/V50 compared to pyrene (Py) in St/Py/C 12Br/V50. Contrary to our expectation, however, increased excimer emission was observed with St/PyMMA/C 12Br/V50 particles, indicating less evenly distributed pyrene chromophores in the particles. The fluorescence lifetime of pyrene chromophores in St/Py/C 12Br/V50 particles was determined to be 286 ns, which was 17 times longer than that of pyrene in THF solution.