Resorbable initiators for polymerizations of lactones

Numerous nontoxic (resorbable) salts were prepared from cations and anions belonging to the human metabolism, such as Na, K, Mg, Ca, Zn and Fe in comb ination with chloride, iodide, hydroxide, carbonate, acetate, stearate, gly colate, L-lactate, D-mandelate and various N-substituted alpha -amino acids . All these salts were used as initiators for polymerizations of L-lactide in bulk at 100 - 180 degreesC. Furthermore, Grignard reagents, hemin and he matin were included in this study. Zn L-lactate was found to be the most us eful initiator in terms of reactivity, maximum molecular weight of the isol ated poly(L-lactide) and its optical purity. Zn L-lactate initiated copolym erizations of L-lactide and glycolid or L-lactide and epsilon -caprolactone were also studied. Finally, first studies of the polymerization mechanism of zinc stearate and tin 2-ethylhexanoate were performed. They suggest that zinc carboxylates combined with an alcohol as coinitiator farm reactive zi nc alkoxides which are the true initiators at temperatures < 150<degrees>C.