Polymorphism of Irganox 1076®: Discovery of new forms and direct characterization of the polymorphs on a medical device by Raman microspectroscopy

SEM image of the surface of a polyurethane catheter with several clusters of needles. As shown by the Raman spectra, these needles correspond to the antioxidant (Irganox 1076) added to the polymer. The polymorph is not the commercially available form but corresponds to one of the three other forms we put into evidence. Irganox 1076® (octadecyl-3,5-di-tert-butyl-4-hydroxyhydrocinnamate) is a common phenolic antioxidant used in many polymer-based medical devices. As with many organic compounds, several polymorphs exist. However, in literature, only two forms of Irganox 1076® have been mentioned. In this study, we were able to produce, by crystallization in different solvents, three distinct polymorphs, which were characterized by DSC, FTIR and PXRD. Moreover, the three polymorphs have long-time stability at ambient pressure and temperature, meaning that they can potentially be present in or on polymeric devices. During DSC measurements, a fourth polymorph, which was only stable at low temperature, was evidenced. Thanks to Raman microspectroscopy, Irganox 1076® was identified directly on commercial polyurethane catheters which exhibited a blooming phenomenon. This study proves that the polymorph identified on the surface is different from the commercially available Irganox 1076®. These results emphasize the importance of the screening of polymorphs before any study of the biocompatibility of antioxidants used in medical devices.