Synthesis of Acrylic-Polyurethane Hybrid Latexes by Miniemulsion Polymerization and Their Pressure-Sensitive Adhesive Applications

The successful incorporation of a NCO-terminated polyurethane (PU) prepolymer in a hybrid miniemulsion is described with the purpose to develop waterborne, high solids, acrylic-PU hybrid nanoparticles to be used in pressure-sensitive adhesive (PSA) applications. To ensure efficient chemical incorporation of the reactive PU into the hybrid latex particles, the NCO moieties were reacted with 2-hydroxyethyl methacrylate (HEMA). The NCO-HEMA coupling reaction was thoroughly studied by conductimetry in order to control the extent of HEMA. incorporation into the PU chains. The resulting HEMA-end-capped prepolymers were chain extended in situ with Bisphenol A (BPA) and polymerized with n-butyl acrylate, methyl meth acrylate, and acrylic acid in the presence of small amounts of a chain transfer agent to form PU/acrylic particles. The amount of chain transfer agent, the ratio between HEMA and BPA, and the amount of PU were varied step by step to study their influence on the final film properties. The miniemulsions and resulting hybrid latexes were characterized in terms of size, monomer conversion, evolution of the ratio of the number of polymer particles to the number of droplets (N-p/N-d), and gel content. In parallel, the mechanical and adhesive properties of the films were tested using probe tack experiments. This allowed us to identify the reaction conditions making it possible to obtain high solids content PU/acrylic hybrid latexes, usable to prepare waterborne pressure-sensitive adhesive films with good adhesive properties, using a simple miniemulsion polymerization method.