Magnetic susceptibility measurements were performed on samples 1-5,c-e with a SQUID magnetometer. The SCO properties (hysteresis width, transition temperature, and HS fraction) of the as-synthesized product can be altered by thermal annealing. This effect occurs due to the recrystallization of the CP inside the polymeric micelles at annealing temperatures above the glass transition temperature Tg of PS (109 °C/382 K, see Figure ), proven by temperature-dependent powder X-ray diffraction (T-PXRD). To investigate the impact of thermal annealing on the different samples, several cooling and heating cycles were made for each sample where the maximum temperature was increased step-wise from 300 K to 370 K, 380 K and 400 K. All measurements were made in the sweep mode with a velocity of 5 K min -1 . After thermal annealing of the samples at 400 K for 1 h, the final measurement was made first in the sweep mode (5 K min -1 ) and then in the settle mode (before each measurement point the temperature was allowed to stabilize, average measurement velocity 0.5 K min -1 ) to allow the investigation of kinetic effects. As representatives, the magnetic properties of the smallest and the largest nanoparticles with five synthesis cycles, 1e and 5e, are displayed as χMT vs. T plots in Figure and B in the temperature range between 300 K and 50 K, to illustrate the differences in the annealing behavior as a function of the particle size and shape. The full temperature range of all samples with all measurement cycles is given in the Supporting Information, Figures . Moreover, the residual HS fraction was calculated from the measurements by dividing the χMT value at 50 K by the starting value at 300 K (Table ).