We next conducted laboratory ex situ experiments to complement the in situ studies. For example, we repeated the ramp heating experiment (using 2 °C/min heating rate) of milling polymorph α and stopped the reaction after reaching 87 °C. Subsequent ex situ PXRD analysis confirmed the presence of both polymorphs in the reaction mixture (ESI Fig. ), thus reproducing the results that we obtained at the synchrotron facility (Fig. ). We were also curious to see if we could lower the thermo-mechanochemical transition temperature even further by varying milling temperature and time parameters. Importantly, after isothermal milling of polymorph α at 81 °C for 1 h, pure polymorph β was obtained (ESI Fig. ). However, further lowering of the milling temperature to 71 °C and extension of milling time to 2 h did not result in a polymorphic transition, which was also the case after continuing to mill the same sample for an additional 24 h at 71 °C (ESI Fig. ). We also performed LAG of polymorph α for 2 h at 71 °C with THF as a liquid additive but α→β transition did not occur (ESI Fig. ). Thus, the lowest detected limit for α→β transition by thermo-mechanochemistry was 81 °C.