Caracterização de latex poliestirenicos por centrifugação em gradiente de densidade

AUTOR(ES)

Jose Machado Moita Neto

DATA DE PUBLICAÇÃO

1994

RESUMO

This thesis contains five parts: Synthesis of polystyrene and poly[styrene-co-(acrylic acid)] latices, containing the basic information on emulsion polymerization together with the procedures used in this work, in the synthesis of PS and PSAA latices. Characterization of the latices of polystyrene and poly[styrene-co-(acrylic acid)], where the products of synthesis are characterized by several techniques: infrared spectroscopy, nuclear magnetic resonance (C and H), X-rays diffraction, transmission electron microscopy, gel permeation chromatography, viscometry and densimetry. Polystyrene latex samples synthesized following the same procedure present similar particle size distributions, but different molar masses. Rheological properties of the polystyrene latex, where the rheological behavior of polystyrene latex in different salt concentrations, particle concentration and in presence and absence of surfactants is described. There is a critical shear stress at low ionic strength, assigned to repulsive forces among latex particles. Centrifugation in density gradient: the technique, which gives the principIes of centrifugation in density gradients. A study on the linearity, stability and reproducibility of the sucrose density gradients used in this work is also presented. Centrifugation of latices in density gradients, presenting the behavior of PS and PSAA latices in sucrose density gradients. The effect of salts and of surfactants on the migration profile of the latex particles is also examined. A PS latex sample in the presence of 10 M de NaCI is divided in three fractions with different densities. This has thus a heterogeneity which has not been evidenced by other methods in the literature, so far. The heterogeneity of the poly[styrene-co-(acrylic acid)] latex is algo evidenced but only in the presence of 3:1 electrolytes.

ASSUNTO(S)

polimerização acido acrilico latex - sintese

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