A quenched-flow reactor is introduced as an effective means for the production of polyolefin particles with precisely controlled reaction times as low as 40 ms. The use of off-line scanning electron microscopy and induced-coupled plasma yields experimental data on the development of the kinetics and morphology of nascent structures during the polymerisation of ethylene on a heterogeneous TiCl4MgCl2 Ziegler-Natta catalyst. Initial ex situ observations revealed the development of specific morphologies very early during the reaction (e.g., cracks in platelike surfaces, fines, extrudates, etc.) that can potentially lead to fines, and the kinetic analysis showed extremely high reaction rates at very short times.