STUDIES OF THE MECHANISM OF CRYSTAL-GROWTH OF HEXAMETHYLMELAMINE .1. SOLUTE SOLVENT INTERACTIONS

The crystal habit of hexamethylmelamine (HMM) obtained by slow crystallization from various solvents was expressed quantitatively in terms of the mass median axial ratio βm. The correlation between βm and the dielectric constant and dipole moment of the solvents was found to be weak (r2≤0.3), although the earlier qualitative relation between the solvent polarity and the crystal elongation was confirmed. Spectroscopic (UV, IR, 13C NMR) and osmometric studies failed to delect any specific solvent- or concentration-dependent solute-solvent interactions, in agreement with the previous studies. It appears that slow crystallization in fact favours formation of "compact" crystals of HMM from polar solvents; the non-polar solvents tend to form "compact" crystals of HMM irrespective of the rate of crystallization. © 1990.