Schiff base derivatives of the biometals (Zn, Mg, Ca) in the presence of anion initiators have been shown to be very effective catalysts for the ring-opening polymerization of trimethylene carbonate (TMC or 1,3-dioxan-2-one) to poly( TMC) devoid of oxetane linkages. The order of catalytic activity as a function of metal was found to be Ca(II) >> Mg( II) > Zn(II). Optimization of the calcium system was achieved utilizing a salen ligand with tert-butyl substituents in the 3,5-positions of the phenolate rings and an ethylene backbone for the diimine along with an azide ion initiator. These conditions led to a TOF of 1286 h(-1) for a melt polymerization carried out at 86 degrees C. Solution studies in tetrachloroethane demonstrated the polymerization reaction to proceed via a mechanism first order in [ monomer], [( salen) Ca], and [ anion initiator] and to involve TMC ring-opening by way of acyl-oxygen bond cleavage. The activation parameters were determined to be Delta H double dagger = 20.1 kJ/mol and Delta S double dagger = - 128 J/( mol K).