Most emulsions use low level functional monomers for targeted end use applications such as adsorption and adhesion, water resistance and ambient crosslinking reactions. The challenge has been to fully characterize the location of these functional monomers in the latex particle. Functional monomers for adsorption property are preferentially placed close to the surface. In this work, we present a novel approach that enables us to probe surfaces as well as deeper into the latex particle for up to about 5-15 nm depending upon the composition of the polymers. The technique involves swelling of the latex particles with mixtures of water and water miscible solvents such as tetrahydrofuran (THF) to hydroplasticize components at the shell of the particle with variable depth based on the amount of THF used. This is followed by T2 (spin-spin relaxation) and diffusion (PFGNMR) filter experiments to remove signals of partially swollen portion of the polymer close to the core of the particle and water soluble species in the aqueous phase, respectively. This leaves only the signals from the hydroplasticized shell of the particle. We have demonstrated the method to probe the location of polymerizable surfactants, aceto acetoxy methacrylate (AAEM) and Diacetone acrylamide (DAAm). While AAEM is distributed throughout the depth we measured (5-10 nm), we detected some portion of DAAm much closer to the surface. We have also shown that changes to synthetic conditions appear to have the ability enhance the amount of DAAm close to the surface. Highly crosslinked latex particles and functional monomers without protonated side group or unique signals may not be accessible by this method.

Distribution of functional monomers in latex particles: PFGNMR study

255th National Meeting (2018)

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