Unintended Rate Enhancement in Mechanochemical Kinetics by Using Poly(methyl methacrylate) Jars

Abstract

Time-resolved in situ (TRIS) X-ray diffraction has changed how mechanochemical transformations are studied but requires the use of X-ray transparent jars often made from poly(methyl methacrylate) (PMMA). However, using PMMA jars can alter the apparent kinetics of mechanochemical polymorphism by an order of magnitude, questioning the interpretability of established TRIS methods. Our results suggest that rate enhancement in PMMA jars may not be dominated by chemical effects of the polymer, but rather a result of different equilibrium temperatures within the jar. These features must be better understood before control over mechanochemical reactions can be achieved.

In situ investigation of controlled polymorphism in mechanochemistry at elevated temperature

“…Though they can appear to be 'brute force' methods, a remarkable degree of control is possible over mechanochemical processes. For example, the outcome of a mechanochemical reaction can be tuned to signicant degrees by including additives (liquid, 18,19 solids, 20,21 or polymers 16,22 ) or by changing the material of the milling jar 16,23,24 and ball. [25][26][27][28] Though it is a natural analogy to solution chemistry, attempts to ne-tune mechanochemical reactions by either controlling the bulk temperature or by changing the magnitude of the input mechanical energy have been less commonly explored, particularly regarding organic materials.…”

Direct in situ measurement of polymorphic transition temperatures under thermo-mechanochemical conditions

“…11 The polymorphic outcome of mechanochemical reactions is highly sensitive to the reaction conditions in neat grinding (NG), liquid-assisted grinding (LAG), 12–15 ion and liquid-assisted grinding, 16 and polymer-assisted grinding 17 approaches. It can also be modified by using different milling jars 18,19 and balls. 20 Notably, polymorphic transitions induced by milling can modify the bulk temperature of the reaction mixture.…”

Direct in situ measurement of polymorphic transition temperatures in thermo-mechanochemical reactions

“…11 The polymorphic outcome of mechanochemical reactions is highly sensitive to the reaction conditions in neat grinding (NG), liquid-assisted grinding (LAG), [12][13][14][15] ion and liquid-assisted grinding, 16 and polymer-assisted grinding 17 approaches. It can also be modified by using different milling jars 18,19 and balls 20 or by avoiding balls completely. 21 Interestingly, Emmerling and Michalchuk have recently shown how thermomechanochemical reactions lowered the polymorphic transition temperature in isonicotinamide and glutaric acid cocrystals by at least 15 °C compared to the corresponding DSC transition temperature.…”