The present study describes the temporary evolution of size and morphology of thermosensitive and biocompatible microgel particles based on ethylene glycol (EG). P-MeO(2)MA-co-OEGMA particles were synthesized by precipitation polymerization. The growth of the microgel particles was analyzed at different reaction times using dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The scattering data show the increase of particle size and swelling capability during the polymerization process. After 60 min further continuation of the polymerization reaction causes no further change of neither external nor internal particle properties. SANS measurements reveal the formation of a dense core, mainly consisting of cross-linker at an early polymerization state. This is followed by the growth of a loosely packed polymer shell. Nanodomains, observed during the volume phase transition (VPT), as well as a second correlation-length of the network fluctuations arise with progressing polymerization reaction related to the buildup of the shell.