Shaohua Shen

Reversible fluorescence modulation of spiropyran-functionalized carbon nanoparticles

Fluorescent carbon nanoparticles (CNPs) with diameters of about 3 nm which can emit blue-green light were synthesized through the hydrothermal carbonization of ethylenediaminetetraacetic acid disodium salt (EDTA·2Na). Then, the CNPs were functionalized with spiropyrans to obtain the spiropyran-functionalized CNPs. The emission of the spiropyran-functionalized CNPs centered at 510 nm could be switched off, while being turned on at 650 nm via energy transfer after UV light irradiation. The process could be reversed by using visible light irradiation. The optical switching of the fluorescence was repeated 10 times without apparent “fatigue”, showing excellent photoreversibility and high stability. Spiropyran-functionalized CNPs may find potential applications in biological imaging and labeling, reversible data storage/erasing, as well as individual light-dependent nanoscale devices.

Preparation of Monodisperse Cationic Microspheres by Dispersion Polymerization of Styrene and a Cation-Charged Monomer in the Absence of a Stabilizer

Cationic polystyrene (PS) microspheres with monodispersity were prepared by dispersion polymerization of styrene and [2-(methacyrloyloxy) ethyl] trimethylammonium chloride (METMAC) in methanol/water system. The effects of METMAC, styrene, and initiator concentration as well as solvent composition on the diameters and size distribution of PS microspheres were systematically investigated. The results indicated that monodisperse cationic PS microspheres could be generated at METMAC concentration less than 2 mol% relative to styrene amount, and too high or low styrene amount was unfavorable to produce cationic PS microspheres. Moreover, it was found that with initiator concentration increasing, the average diameter and the size distribution of cationic PS microspheres also markedly increased. Solvent composition played a significantly important role in the preparation of cationic PS microspheres by dispersion polymerization of styrene and METMAC. Finally, the possible growth and stabilization mechanism of cationic PS microspheres was proposed. The electrostatic repulsion derived from positive charge on the surface of PS microspheres was responsible for the stabilization during dispersion polymerization in the absence of a stabilizer.

A Novel Route to Prepare Cationic Polystyrene Latex Particles with Monodispersity

Relatively clean cation-charged polystyrene (PS) latex particles were prepared via a novel and simple route in the absence of steric stabilizers. The reaction system only included medium, styrene, and initiator with quaternary ammonium moiety. The influences of initiator concentration, and medium composition on the diameter and size distribution of PS latex particles were systematically investigated. The particle morphology and size, the surface N content, and the particle size distribution were respectively determined by SEM, XPS, and laser particle size analyzer. The results indicated that monodisperse and cation-charged PS latex particles with diameter of 0.45–0.95 μm could be successfully produced via the simple reaction system, and cationic initiator concentration played a key role in the preparation of uniform PS latex particles. Finally, a plausible mechanism was proposed for explaining nucleation, growth, and stabilization of PS latex particles.

Functional block copolymers from controlled radical and ring opening polymerization

Three techniques of controlled radical polymerization, namely nitroxide-mediated radical polymerization (NMRP), atom transfer radical polymerization (ATRP), and reversible addition-fragmentation chain transfer (RAFT) polymerization in combination with ring opening polymerization (ROP) were employed to prepare functional block-copolymers with controllable molecular weight and narrow molecular weight distribution. The structure, molecular weight, and PDI of block-copolymers were characterized by various techniques. The synthesis routes of NMRP-ROP, ROP-ATRP, and ROPRAFT exhibited excellent controllable features in the preparation of functional block-copolymers.