Quantitative reversible one pot interconversion of three crystalline polymorphs by ball mill grinding.

11 February 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


We demonstrate here using a disulfide system the first example of reversible, selective and quantitative transformation between three crystalline polymorphs by ball mill grinding. This includes the discovery of a previously unknown polymorph. Each polymorph is reproducibly obtained under well-defined neat or liquid-assisted grinding conditions, revealing subtle control over the apparent thermodynamic stability. We discovered that presence of a contaminant as low as 1.5% mol mol-1 acting as a template is required to enable all these three polymorph transformations. The relative stabilities of the polymorphs are determined by the sizes of the nanocrystals produced under different conditions and by surface interactions with small amounts of added solvent. For the first time, we show evidence that each of the three polymorphs is obtained with a unique and reproducible crystalline size. This mechanochemical approach gives access to bulk quantities of metastable polymorphs that are inaccessible through recrystallisation.


ball mill grinding
reversible polymorph interconversion

Supplementary materials

Supplementary Material
Details on materials, experimental methods, and computational methods.


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