Morphological Transitions in Fluorinated and Non-Fluorinated Parylenes

A study of temperature-induced crystallinity changes in fluorinated and nonfluorinated parylene thin films using differential scanning calorimetry, thermal stress and wide angle x-ray diffraction measurements is presented. The nonfluorinated parylene (ppx-N) is shown to undergo two phase transitions between 200°C and 300°C. Both transitions show at least some degree of reversibility. The high temperature (β1 -β2) transition is accompanied by a sudden shift in stress, which is attributed to a contraction of the polymers chains. A single, reversible phase transition, occurring between 360°C and 400°C, is observed for fluorinated parylene (ppx-F). This transition is likewise marked by a significant shift in stress, and is apparently due to a similar chain contraction.