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Molecular structure plays a crucial role in determining the final properties of pressure-sensitive adhesives. Here, we demonstrate that the molecular structure of polyurethane/(meth)acrylic hybrids synthesized by miniemulsion photopolymerization changes during storage of the dispersion at room temperature because of the spontaneous formation of nanogels by the assembly of polymer chains within the polymer particles. Analysis of the nanogel structure by asymmetric-flow field-flow fractionation allows identification of the molecular structure that provides the unusual combination of high tack adhesion and excellent shear resistance at high temperature [maximum value of the shear-adhesion failure temperature (SAFT) test, >210 °C].

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Hybrid polyurethane/acrylic particles have been synthesized by miniemulsion polymerization at various temperatures to determine the effect of the reaction temperature on the polymer microstructure and the adhesive properties of films prepared from latexes. Simultaneous free radical polymerization of a mixture of (meth)acrylic monomers in the presence of 2‐hydroxyethyl methacrylate and addition polymerization of an isocyanate terminated prepolymer and chain extending diol have been performed and the resulting polymers are characterized in terms of their gel content, sol molecular weight, swelling degree, and microgel size. The changes in the polymer microstructure are related to bulk effects in the adhesive films resulting from differences in the polymerization kinetics at different temperatures.

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