Study On Synthesis And Oxidative Degradation Characteristics Of Biomedical Degradable Polyesterurethane Networks

In this thesis crosslinked degradable polyesterurethane networks were synthesized from D,L-lactic acid, glycolic acid, 2,2,4- and 2,4,4-trimethylhexamethylene diisocyanate (TMDI), isophorone diisocyanate (IPDI) as raw materials and pentaerythritol as initiator, then H2O2/CoCl2 system was used as an oxidative environment to investigate the in vitro degradation behavior of the crosslinked polyesterurethane networks.Firstly, D,L-lactide was synthesized from D,L-lactic acid with zinc powder as catalyst,and glycolide from glycolic acid using Sb2O3 as catalyst. The resulted D,L-lactide and glycolide were found to have ring structure by fourier transform infrared (FTIR) spectrometry and proton nuclear magnetic resonance(1H NMR) spectrometry. Then two star-shaped oligomers with designed molecular weights (Mn) 5000 g mol-1 and 10000 g mol-1, respectively, were synthesized from D, L-lactide and glycolide as raw materials and pentaerythritol as initiator under catalysis of dibutyltin oxide (DBTO). The oligomers were found to be random copolymers by means of hydroxy titration, attenuated total reflectance fourier transform infrared (ATR-FTIR) spectrometry, 1H NMR and DSC. The molecular weights according to hydroxy titration, GPC and 1H NMR were similar to designed molecular weights. The crosslinked polyesterurethanes with different structures were synthesized by reaction of synthesized prepolymers with TMDI, IPDI using stannous octoate as catalyst. ATR-FTIR and DSC measurements showed that the polyesterurethane networks were amorphous and had crosslinked structures.The oxidative degradation characteristics of the polymer networks PULGT10 were investigated in different concentrations of H2O2/CoCl2 solution, contrasting with degradation of PULGT10 in 0.01M hydrochloric acid solution. Weight loss, water absorption, mechanical properties, volumetric swelling degree and gel content were determined as a function of degradation time. ATR-FTIR and DSC analysis were also used to investigate the process of the polymer networks. The results showed that the H2O2/CoCl2 system could effectively accelerate the degradation of the polyurethanes. The increase of H2O2 concentration could enhance the degradation of the polymer networks, while the change of CoCl2 concentration had little effect on the degradation.