Controlling the Morphology of Film-Forming, Nanocomposite Latexes Containing Layered Double Hydroxide by RAFT-Mediated Emulsion Polymerization

Stable nanocomposite latexes with sandwich, encapsulated, or armored morphology were produced by starved-feed emulsion polymerization in the presence of layered double hydroxide (LDH) nanoparticles. Four statistical copolymers of acrylic acid (AA) and n-butyl acrylate (BA) were adsorbed on the LDH surface, and a film-forming methyl acrylate (MA)/BA (8:2 mass/mass) monomer feed was chosen to facilitate subsequent film formation under ambient conditions. P(AA (17.5)-co-BA(175))-R (R = RAFT function) produced the sandwich morphology, while P(AA(7.5)-co-BA(7.5))-R gave the encapsulated morphology, which is remarkable given that nonencapsulated morphologies are normally considered to be the preferred equilibrium structures for nanocomposite particles. Adsorption behavior and monomer conversion profiles were very similar for the two systems, and we tentatively ascribe the morphological difference to the higher density of RAFT functions in the P(AA(7.5)-co-BA(7.5))-R system. A RAFT-free analogue produced armored latexes, highlighting the importance of the RAFT function for promoting growth of the polymer shell from the nanoparticle surface.