Studies on the effect of virtual crosslinking on the hydrolytic stability of novel aliphatic polyurethane ureas for blood contact applications

The effect of virtual crosslinking on the hydrolytic stability of completel y aliphatic novel poly(urethane ureas), HFL9-PU1 (hard-segment content 57.5 %) and HFL13-PU2 (hard-segment content 67.9%) based on 4,4'-methylene bis(c yclohexyl isocyanate) (H12MDI)-hydroxyterminated polybutadiene-1,6-hexameth ylene diamine, was studied. Fourier transform infrared-attenuated total ref ectance and wide-angle X-ray diffraction studies revealed hydrogen-bonding interaction and microphase separation and formation of crystallites by shor t- and long-range ordering in hard-segment domains. Three-dimensional net-w orks from hydrogen bonding in the present polymers lead to virtually crossl inking and insolubility. These polymers were noncytotoxic to L929 fibroblas t cells. The hemolytic potential is below the accepted limit. The studies o n in vitro biostability in Ringer's solution, phosphate buffered saline, an d papain enzyme revealed no weight loss. The infrared spectral studies reve aled changes in the surface, especially on HFL9-PU1 aged in Ringer's soluti on and phosphate buffered saline, and no changes when aged in papain. The m arginal changes noticed in tensile properties were attributed to the change s in degree of hydrogen bonding and associated rearrangement of molec;lar s tructure in the bulk. The results revealed that the lesser the crosslinking in virgin polymer, the higher the crosslinking in aged polymer and vice ve rse. Increased crosslinking during aging provided increased tensile propert ies in the aged polymer over the virgin polymer and vice versa. For compari son, an aliphatic polyetherurethane urea (HFL16-PU3) was also synthesized u sing poly(oxy tetra methylene glycol) in addition to the above reactants. T hough both HFL9-PU1 and HFL16-PU3 contained the same hard-segment content, the aged sample of the latter showed decreased tensile properties with incr eased crosslinking during aging in contrast to the former. This was attribu ted to less microphase separation in the virgin HFL16-PU3 polymer. (C) 2001 John Wiley & Sons, Inc.