Laminar Entrained Flow Reactors were examined to determine whether this type of reactor can be used to measure the kinetic parameters of the pyrolysis reaction of polymers. In case the EFR was operated in the turbulent regime or the diameter of the reactor was to small, sticking of polymer to the reactor wall, became a major problem. In the laminar flow regime this problem did not occur and this operation regime was determined as a function of the Reynolds number. Due to the necessity of operation in the laminar regime significant temperature and velocity gradients exist in the EFR. To correct for these gradients a model was developed incorporating the Navier - Stokes equations to describe the gas phase velocity and temperature distributions and a single particle model to describe the conversion of the individual particles. While correction of the experimental data for the axial gradients proved to be possible, it was not possible to correct this data for radial gradients in the reactor due to the uncertainty in the radial position of the particle. Experiments were performed and corrected for the aforementioned gradients to obtain the first order kinetic parameters for the pyrolysis of LDPE. However, these parameters are inaccurate and therefore a LEER is preferably not to be used to determine kinetics of particles, if operation of the EFR in the laminar regime is necessary (sticking particles). If possible (non sticking particles) the EFR should be operated in the turbulent regime. Finally our pyrolysis experiments of LDPE showed that intermediate wax - like products are produced during the pyrolysis reaction, which are pyrolysed further in the gas phase.