Plasticizer free curing compositions comprising small particle size complexes of methylenedianiline and an alkali salt, e.g. a 3:1 coordination complex of MDA/alkali salt, with average diameter 60 micron or less, often 20 micron or less, e.g., 10 microns or less, dispersed in a volatile, non-polar, organic solvent are prepared. Stable one pack urethane compositions comprising the plasticizer free curing compositions and polyurethane prepolymers are prepared, which exhibit excellent storage stability and overcome many of the drawbacks encountered when using MDA complexes dispersed in plasticizers such as high boiling aromatic and alkyl di-esters.