Solvent-free describes a process or formulation that proceeds without a liquid medium, so that reactants, catalysts or coating components meet as solids, melts or gases ^[1]. In polymer processing the term covers melt extrusion, solid-state shear and reactive extrusion, where the polymer itself serves as the reaction medium ^[2]. In organic synthesis it denotes reactions run by grinding, by heating the neat reactants or under microwave irradiation, in which the absence of dilution raises the effective concentration of the reacting groups ^[2]. Removing the solvent also removes the drying step and the residual-solvent specification, and it takes away the medium that would otherwise dissipate heat or dissolve an intermediate ^[3].