Ionic autocrosslinking of water-based polymer latices: A new concept of acid–base interaction occurring upon film formation

Latices of the terpolymer styrene/butyl acrylate/acido-basic monomer, the monomer having either a basic chemical group or an acidic chemical group, were separately prepared by free-radical emulsion polymerization using the nonionic surfactant poly(oxy-1,2-ethanediyl) as steric stabilizer. The basic polymer latices were prepared using 1, 3 or 5% of 2-(dimethylamino)ethyl methacrylate, whereas the acidic polymer latices were prepared using 1, 3 or 5% of acrylic acid (mol% relative to conventional monomers, styrene and butyl acrylate). Blends of the basic and the acidic polymer latices were prepared by simply mixing equal molar quantities of basic and acidic latices. The resulting blends were stable as the steric stabilization prevented unlike particles from colliding. Upon film formation, coalescence of the particles took place, with formation of ionic clusters due to proton exchange from the acidic monomer units to the basic monomer units of neighbouring unlike particles. This constitutes a reversible ionic crosslinking at the periphery of neighbouring particles, which affects the various film properties to different extents.