Homopolymer polyamides derived from pairs of diamines and diacids (or diacid derivatives). It can also be accomplished using diisocyanates in place of diamines. Condensation of the diesters with diamines gives cyclic diamides. The ligands are typically derived from alkyl diamines and aromatic aldehydes. Cyclic thioureas are prepared by transamidation of thiourea with diamines. They are structurally and biosynthetically related to the diamines putrescine and cadaverine. Amidoamines are a class of chemical compounds that are formed from fatty acids and diamines. Longer chain diamines, which are "floppy", tend not to form chelate rings. Like other diamines, it is a curing agent for epoxy resins. Chiral diamines and amino alcohols have also been used to modify LAH for enantioselective reductions. The aromatic diamines have a low basicity that provides additional challenges to synthesis. Diamines form a wide range of coordination complexes. The term "diamine" refers mostly to primary diamines, as those are the most reactive. Diamines are used as monomers to prepare polyamides, polyimides, and polyureas.