Influence of Lipid Sorption on Fatigue Strength of Segmented Poly(urethaneurea)s with Various Hard Segment Component

The relationships between aggregation states of hard segments in segmented poly(urethaneureas) and fatigue behavior after lipids sorption are reported. The SPUU used in this study consists of hard and soft segments. The soft segment is composed of poly(tetramethylene glycol) (PTMG) with number average molecular weight of M_n and 4,4′-diphenylmethane diisocyanate (MDI). The hard segment consists of MDI and various diamines. The temperature dependences of infrared spectra and dynamic viscoelasticity revealed that the aggragation of hard segment is stronger for the hard segment consisted of MDI-ethylenediamine (EDA) (Biomer®) or MDI-1,2-propylenediamine (PDA) (TM M_n) than for the one consisted of the random sequence of MDI-EDA and MDI-4,4′-diaminodiphenylmethane (DAM) (TU M_n). The degree of phase mixing between the hard and soft segments in TU M_n is more extensive than that in TM M_n, The specimen after immersing in lipids solution showed weight increase due to lipids sorption. The amount of increase in weight after lipid sorption was larger for TU M_n than for TM M_n. Also, the temperature dependences of dynamic viscoelasticity of the specimen after imersing in lipids solution revealed that disordered hard segments of TU M_n lost their aggregation strength after lipids sorption. The fatigue strength of TU M_n after lipids sorption decreased extensively and showed the formation of microcracks near fatigue fracture surface. This is attributed to the adsorbed lipid. However, TM M_n and Biomer did not show reduction of fatigue strength after lipids sorption. These results indicate that SPUU with disordered hard segments loses its fatigue strength in a biological environment.