Determination of chemical decay mechanisms of Parylene-C during X-ray irradiation using two-dimensional correlation FTIR

Parylene (poly-p-xylylene), and its family of halogenated variants, have a long history for application as protective coatings and dielectric barriers. Among them, Parylene-C is the most popular due to its high impermeability to moisture, resistance to corrosive environments, and its vapor deposition polymerization, which is self-initiated and unterminated creating an extremely pure polymer coating. In order to apply these advantageous material characteristics in an environment containing ionizing radiation the effects of irradiation on the chemical stability of the polymer throughout the lifetime of the material needs to be further understood. In this work, Fourier-transform infrared (FTIR) and two-dimensional correlation (2D-COS) spectroscopies were used to monitor the structural changes in a similar to 25 mu m freestanding film of Parylene-C after subjection to X-ray irradiation. Samples were exposed to X-ray doses up to 100,000 Gy in atmospheric conditions, and IR spectra were measured after each 500Gy dose. Using 2D-COS it was possible to gain insight into the chemical stability and temporal mechanisms of the chemical reactions accompanying X-ray radiation of Parylene-C. Oxidation was observed by the production of a new species absorbing in the IR at 1697 and 1740 cm(-1). Additionally, skeletal stretching of the aliphatic back bone were positively correlated to C-O oxidation products found in the region of 1425-1100 cm(-1). The present work is confirmation that Parylene-C does experience chemical degradation from x-ray dose caused by oxidation of the polymer structure. (C) 2019 Elsevier Ltd. All rights reserved.