The effect of pre-set extension on the degree of hydrolytic degradation in multicomponent polyurethane elastomers

The impact of pre-set extension on the degree of hydrolytic degradation in all-aliphatic polyurethane (PU) films was tested in phosphate-buffered saline (PBS) for a period of up to 12 months. The PUs were synthesized from polycarbonate-based macrodiol (MD), diisocyanate-1,6-hexane (HDI), butane-1,4-diol (BD) and d,l-lactide-based oligomeric diol (DLL). Macrodiol with molecular weights of ∼2800 Da, three DLL oligomers (∼400, 660 and 850 Da) and three MD-to-BD-to-DLL molar ratios were chosen for PU synthesis. The isocyanate-to-total-hydroxyl-group ratio was kept constant at 1.05. The functional properties of raw polyurethane films and the samples immersed for 1, 3, 6, 9 and 12 months in a model physiological environment (37 °C, pH = 7.4) were studied. The pre-set extension varied from 20 up to 150% and was applied on PUs with or without any DLL. The given pre-set strain had only slight – but varying – influence on the extent of the hydrolytic process, compared to the non-extended analogues. In samples that underwent efficient orientation and crystallization under strain (three-component PU and PU containing DLL ca. 400 Da), the degradation process was slightly inhibited compared with that of the unstrained analogues. If the systems were composed of sequences not capable of efficient crystallization under strain (PUs containing DLL ca. 660 and 850 Da), then the hydrolytic degradation of the pre-strained samples was accelerated. The observed changes in the functional properties of the mechanically strained PU materials subjected to the long-term hydrolytic process under physiology-mimicking conditions are important for potential medical, package coating, and film applications.