Dithiothreitol-based polyurethanes. Synthesis and degradation studies

The synthesis, characterization, and some properties of new copolyurethanes are described. These copolyurethanes were obtained by reaction of 1,4-di-S-benzyl-d,l-dithiothreitol (DTTSBn) and triethylene glycol (TEG) with 1,6-hexamethylene diisocyanate (HMDI). The copolymer compositions were studied by 1H NMR, revealing that the content of the copolymer units is in good agreement with that of their corresponding feed. The PU(TEG-HMDI) homopolymer exhibited a high crystallinity, but the introduction of the DTTSBn diol led to a reduction in the crystallinity of the copolymers and an increase of the stiffness, with associated increases in the Tg values. In their TG curves, the copolymers exhibited a mixed trend of the related homopolymers; all of them were thermally stable, with degradation temperatures above 250 °C and with higher thermal resistance displayed by the polymers with higher TEG contents. The chemical and enzymatically catalyzed hydrolytic degradations of the macromolecules were tested. PU(TEG-HMDI) was the only polymer degraded under physiological conditions, but an increase of temperature markedly affected the degradation rates. Two proteolytic enzymes (papain and α-chymotrypsin) and two esterase enzymes (cholesterol esterase and lipase) were chosen to perform enzyme-mediated hydrolysis trials, the first reported use of pancreatic lipase for urethane-bond hydrolysis in polyurethanes.