We then turned to thermo-mechanochemical reactions with simultaneous mechanical and thermal activation and monitored them in situ by synchrotron PXRD (Fig. , ESI Figs. Please do not adjust margins Please do not adjust margins S6 and S7). In the first experiment, we used a ramp heating rate of 2 °C/min for milling of polymorph α (for details see ESI). Time-resolved in situ PXRD data showed the onset of a polymorphic transition to polymorph β after 30 min of milling (Fig. and) when the temperature of the milling reactor reached 86 °C (Fig. ). Both polymorphs co-existed until the milling temperature reached 90 °C, after which only polymorph β was present, thus indicating a completion of the α→β transition. In the second experiment, the obtained polymorph β was milled under LAG conditions with n-pentane as a liquid additive at room temperature. After ca. 6 min of milling, we observed a gradual disappearance of the diffraction peaks corresponding to β (ESI Fig. ). However, we attributed this feature to the change in the rheology of the reaction mixture § and the inhomogeneous distribution of the milled sample, which led to its disappearance from the X-ray beam. Nevertheless, the same sample was again milled but this time heated at a faster rate without ramp heating (Fig. ). Immediately after the heating started, we observed the appearance of diffraction peaks, which at the temperature of 73 °C were more pronounced and clearly showed the presence of α (Fig. ). In continuation of the same experiment, the onset of the α→β transition was observed at 100 °C after only 4.4 minutes of milling and finished after 4.9 min of milling at a milling temperature of 108 °C (Fig. and). Hence, thermomechanochemical experiments with different heating rates demonstrated that both milling temperature and time markedly influence the polymorphic transition temperature.