Synthesis, Characterization And Degradation Behavior Of Biodegradable Polyurethanes

Biodegradable polyurethane materials, which possess excellent properties, such as good biocompatibility, mechanical properties, and facile formation, etc, have been widely applied as biomaterials in medical treatment. In this article, the star-shaped hydroxy-telechelic cooligoesters were synthesized via ring-opening polymerization at 130℃, using lactide and glycolide as comonomers, pentaerythritol as initiator and dibutyltin oxide (DBTO) as catalyst. Then crosslinked polyurethanes were prepared from those cooligoesters and isophorone diisocyanate (IPDI) as junction unit. The absorption peaks of N-H at 3391cm-1 and 1525cm-1 in ATR-FTIR revealed the hydroxyl group had involved in the reaction. The DSC curves showed only one glass transition temperature at 57℃, which testified synthesized polyurethanes were amorphous. The gel content of polyurethanes was above 90%, but the polyurethane prepared from the cooligoester with a number average molecular weight (Mn) of 7K had a gel content of 89%.The degradation behavior of the polyurethane were investigated in phosphate-buffered saline (pH=7.0) at 37℃by examining changes in weight loss, water absorption, volumetric swelling degree, gel content and mechanical properties during the degradation. The results showed the polyurethane with Mn = 3K of cooligoester degradated slowly, weight loss was only 2.5% in 60 days. The polyurethane with Mn = 7K of cooligoester degradated rapidly due to low gel content, the weight loss was up to 40% in 70 days. As for polyurethanes with Mn = 5K of cooligoester and Mn = 10K of cooligoester, the weight loss, water absorption and the ratio of volumetric swelling degree(Qt/Q0) decreased with the increasing of molecular weight of cooligoester, while they increased with the increasing of glycolide content in cooligoester with a comparable molecular weight. During the degradation the gel content of polyurethanes decreased gradually, while weight loss, water absorption and swelling degree increased gradually. Tensile test showed the polyurethanes before degradation were fragileness, and had the Young's modulus above 400 MPa, the tensile strength above 40 MPa, the elongation at break around 10%. Mechanical properties decreased gradually during degradation. As for polyurethanes with Mn = 5K of cooligoester and Mn = 10K of cooligoester, Young's modulus and tensile strength...