Molecular structure plays a crucial role 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 the storage of the dispersion at room temperature, because of the spontaneous formation of nanogels by assembly of polymer chains within the polymer particles. Analysis of the nanogel structure by asymmetric-flow field-flow fractionation allows identifying 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 test (SAFT), >210 ºC).