Date of Award
Program or Major
Doctor of Philosophy
Emulsion polymerization is a multiphase reaction process and the overall kinetics depend on the reaction rates in both the aqueous and particle phases. The morphology development within composite latex particles is controlled by both kinetic and thermodynamic factors. Functional monomers like acrylic acid and 2-hydroxyethyl methacrylate are widely used in emulsion polymerization at low concentrations (usually < 10% to total monomers) to improve various properties like shear and freeze thaw stability of the latex, adhesion of the polymer to metal and paper, and to create the possibility for post-polymerization chemical modifications. These monomers are highly water soluble and very much more polar than the commonly used acrylate and styrene monomers. This dissertation deals with the effect of such functional monomers on the reaction kinetics during the emulsion polymerization and on the resulting morphology of the composite latex particles.
A detailed examination of the distribution behavior of vinyl acid and hydroxy (meth)acrylate functional monomers between the nonfunctional monomer phase and the aqueous phase is reported here. Due to the dimerization and multimer formation capabilities of vinyl acid and hydroxy (meth)acrylate monomer via hydrogen bonding, the distribution of these monomers between aqueous and organic phases can be highly concentration dependent. In addition, the distribution of vinyl acids is a strong function of pH. Common emulsion polymerization with functional monomers uses more than one nonfunctional monomer. We found that the distribution of functional monomers can be effectively predicted for multicomponent nonfunctional monomer mixtures using appropriate `mixing rules'. The distribution of a monomer between the aqueous phase and the polymer particle phase is normally estimated using monomer-polymer Flory-Huggins interaction parameters and we have carefully determined such parameters for the functional monomers and various polymers examined in this work.
From the experimental and simulation studies for seeded emulsion copolymerizations with functional monomers, we found that both the aqueous phase and the particle phase kinetics are affected by these monomers. The functional monomers produced longer oligoradicals (Z-mers) in the water phase which then entered the particles to promote polymerization. Moreover, the distribution studies revealed an increase in the water phase monomer concentrations when these functional monomers were present. Both of these phenomena combined to result in an increase in the radical entry rate into the particles as compared to reactions without functional monomers under similar conditions.
The particle morphologies obtained from seeded emulsion polymerizations with functional monomers were characterized and compared to those without the functional monomers. In these studies the levels of the functional monomers were varied between 0% and 10% and the polarity differences between the seed and second stage polymers changed in different directions depending on the particular system. For all of the systems studied, it was found that for the cases where the final particle morphology was either at or close to equilibrium (in terms of the minimization of free energy), the incorporation of the functional monomers did not impact the morphology significantly. However for the cases where the final morphologies were kinetically controlled, increases in the amount of functional monomer in a nonpolar second stage monomer increased the amount of phase mixing with a polar seed polymer.
Tripathi, Amit Kumar, "TOWARDS THE UNDERSTANDING OF THE EFFECT OF FUNCTIONAL MONOMERS ON LATEX PARTICLE MORPHOLOGY FORMED BY EMULSION POLYMERIZATION" (2014). Doctoral Dissertations. 2157.