Novel Synthesis of Multi-Scaled, Surfactant-Free Monodisperse Latexes via Alcoholic Dispersion Polymerization in a Mixed Ionic/Nonionic Initiation System
journal contributionposted on 14.05.2013 by I-Chen Chou, Wen-Yen Chiu
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We propose a new strategy for preparing high solid content, surfactant-free charge stabilized monodisperse latex particles via alcoholic dispersion polymerization by means of a mixed inoic/nonionic initiator system, which produces hundreds of nanometer up to several micrometer sized latex particles with a clean surface in a single batch process. Two criteria should be met to produce these electrostatically stabilized uniform size latexes: (1) The ionic initiator chosen should have a greater or comparable decomposition rate to the nonionic initiator. (2) A relatively small amount of ionic initiator to the nonionic initiator should be employed in the polymerization. The electrostatic stabilization is solely provided by the ionic fragments arising form the ionic initiator in the absence of any stabilizer, and the addition of nonionic initiator has increased the latex uniformity through the enhancement of particle seeds formation at the nucleation stage also the perferred particle phase polymerization after nucleation. The ultimate particle sizes are predominantly controlled by the medium solvency, the polymerization temperature, the concentration of nonionic initiator, and the types of mixed initiator pairs empolyed. A perlonged particle number (Np) variation to the conversion before it reaches a constant is observed, which would be the most stricking difference between the nucleation characteristics in classical dispersion polymerization (usually has unchanged Np below 1% monomer conversion) or soapless polymerization. It is shown that highly monodisperse latex can be formed in wide range of monomer and initiator concentrations also a considerable temperature range. The effect of various factors on this new approach is investigated, and a sepcific mechanism is also presented.