Biodegradable polyurethanes with potential for applications in medical implants were synthesized in bulk with aliphatic hexamethylene diisocyanate, isophorone diisocyanate, poly(epsilon -caprolactone) diols of various molecular weights, 1,4-butane diol, 2-amino-1-butanol, thiodiethylene diol, and 2-mercaptoethyl ether chain extenders. The catalysts used were stannous octoate, dibutyltin dilaurate, ferric acetyl acetonate, magnesium methoxide, zinc octoate, and manganese 2-ethyl hexanoate. The synthesis reactions were second-order. All the materials had narrow, unimodal molecular weight distributions and polydispersity indices of 1.5-1.9. The chemical structures of the polyurethanes, as assessed from H-1 NMR and C-13 NMR spectra, were in good agreement with the monomer stoichiometric ratios. The glass-transition temperatures of the materials ranged from -38 to -57 degreesC and were higher for polymers based on isophorone diisocyanate and with higher hard-segment contents. For polyurethanes with the same hard-segment content, there was no effect of the material molecular weight on the thermal properties. The tensile strengths of the materials were 12-63 MPa, and the tensile moduli were 8-107 MPa. These increased with an increasing hard-segment content. The least effective catalyst was magnesium methoxide, and the most effective was ferric acetyl acetonate. Stannous octoate and manganese 2-ethyl hexanoate were less effective than dibutyltin dilaurate and zinc octoate.