Polymer/Laponite Nanocomposite Films Produced from Surfactant-Free Latexes Using Cationic Macromolecular Reversible Addition-Fragmentation Chain Transfer Copolymers

In this work, the use of positively charged macromolecular reversible addition-fragmentation chain transfer (RAFT) copolymers (macro-RAFTs) in the synthesis of Laponite RD-based nanocomposite latex particles is described. For this purpose, two different amphiphilic copolymers composed of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and n-butyl acrylate (BA) units are investigated. In the first step, the macroRAFT is adsorbed onto Laponite, and then, in the second step, the macroRAFT-modified clay platelets are used in the emulsion copolymerization of methyl methacrylate (MMA), methyl acrylate (MA), or styrene (Sty), with BA. By acting as both coupling agents and stabilizers, the macroRAFT agents lead to the formation of partially encapsulated particles and dumbbell structures. When hydrophobic monomer mixtures that can form film are used, these morphologies result in nanocomposite films with increased stiffness, in comparison to the pure polymer matrix. As observed by dynamic mechanical analysis, the high Young's modulus level presented by the composite films in the rubbery plateau (above 100 MPa when filled with 10 wt% of clay) highlights the strong mechanical reinforcement. Such an improvement can be attributed to the formation of two percolating networks, one of homogeneously distributed and connected platelets and one of macroRAFT chains, within the polymer matrix.