Dirk-Olaf Damrau

Polylactones, 42. Zn L-lactate-catalyzed polymerizations of 1,4-dioxan-2-one†‡

1,4-Dioxan-2-one (DOXA) was polymerized by means of Zn L-lactate (ZnLac 2 ) as catalyst in bulk. Upon systematic variation of the temperature, the reaction time and the monomer/catalyst (M/C) mole ratio the highest molecular weights were obtained at 100°C and M/C ratios between 2000 and 4000. However, long reaction times (8-14d) were required to obtain optimum results. Zinc chloride proved to be a somewhat less reactive catalyst, whereas zinc bromide proved to be as efficient as ZnLac 2 . Addition of benzyl alcohol as a coinitiator at a fixed DOXA/ZnLac 2 ratio allowed a systematic control of the molecular weight. Furthermore the formation of benzyl ester endgroups was detected. Moreover, ZnLac 2 allows the incorporation of various bioactive alcohols or phenols (e.g. testosterone, stigmasterol, ergocalciferol, cortisone, α-tocopherol) in the form of ester endgroups. Finally several properties of polydioxanone are reported and discussed, such as solubilities, IR, 1 H NMR and 13 C NMR spectroscopic data and thermogravimetric analysis.

Polylactones, 43. Polymerization of L-lactide catalyzed by zinc amino acid salts†

The usefulness of the zinc salts of five different amino acids or amino acid derivatives as polymerization catalyst of L-lactide was studied and compared. The five amino acid (derivatives) were: N-acetyl-glycine. N-tosylglycine. L-proline, L-pyroglutamic acid and N-acetyl-4-aminobenzoic acid. All polymerizations were conducted in bulk. Due to the low reactivity of all Zn catalysts a reaction temperature of 150 C was needed to obtain yields around 90%. While the basic Zn prolinate caused partial racemization, the neutral Zn salts yielded poly(L-lactides) with 97-100% optical purity. Regardless of catalyst and reaction conditions only moderate molecular weights were obtained.

Polylactones. 44. Polymerizations of L-Lactide Catalyzed by Manganese Salts

Abstract Manganese(II)chloride, bromide, acetate and L-lactate were used as catalysts for the polymerization of L-lactide. All polymerizations were performed in bulk and despite a high reaction temperature (150°C), long reaction times (192 hours) were needed to achieve nearly complete conversions. Mn L-lactate was found to be the most reactive of the four catalysts. Yet, relatively low molecular weights (Mv = 33 000) and partial racemization were found under all circumstances. Furthermore, copolymerizations of L-lactide and glycolide or L-lactide and e-caprolactone were studied. A few homopolymerizations of L-lactide catalyzed by magnesium lactate or calcium lactate were included for comparison. These more basic initiators gave even worse results.