Kinetically controlled polymorphism and amorphization of 1-methylpiperidine under high hydrostatic pressure

Phase transformations of 1-methylpiperidine under static and dynamic compression up to 21 GPa were investigated via in-situ Raman spectroscopy in a diamond anvil cell. Static compression reveals at least three crystalline phases and an amorphous state, which are kinetically sensitive and metastable. Dynamic compression rapidly induces amorphization, and subsequent decompression leads to spontaneous crystallization through Phase III and Phase II. The high-pressure phase behavior of 1-methylpiperidine is kinetically controlled rather than purely thermodynamic, governed by structural evolution, molecular flexibility, and metastable state formation.