Simultaneous free radical and addition miniemulsion polymerization: Effect of the diol on the microstructure of polyurethane-acrylic pressure-sensitive adhesives

Water-borne polyurethane/acrylic hybrid latexes for their application as pressure-sensitive adhesives were prepared by high solids simultaneous free radical and addition miniemulsion polymerization. In these polymerizations, the polymer network was formed by polyurethane chains that were linked to acrylic chains by the joint reaction of a hydroxyl functional methacrylate and an isocyanate functional polyurethane prepolymer, and by acrylic chains linked among themselves. Under the working conditions, the modification of the polymer architecture was possible by altering the acrylic chains, the polyurethane chains and the links between the polyurethane and the acrylic chains. In the present work, the polymer microstructure was modified by the addition of different diols (polyurethane chain extenders) to the formulation. The effect of the nature of the diol on polymerization kinetics, polymer microstructure and adhesive performance of water-borne PSAs was studied. Adhesive test results demonstrate clearly for the first time that the long-term resistance to shear of an acrylic PSA does not depend only on its gel content but very much depends on the detailed microstructure of the gel inside each particle.