Study on the orientation structure and thermal dimensional stability of polyimide films based on infrared dichroism method.

A series of uniaxially oriented polyimide (PI) films were fabricated via hot drawing at varying temperatures and draw ratios, and their orientation structure and thermal dimensional stability were investigated in detail. The infrared dichroism based on C = O symmetrical stretching was employed to effectively determine the orientation of chain segments. Other characteristic peaks, such as C = O asymmetric and C-N stretching, were highly sensitive to the geometric structure of chain segments, thereby providing a valuable means for comprehending their morphology. It has been observed that lower thermal expansion coefficient (CTE) can be achieved through low-temperature stretching, while high-temperature stretching is more effective in suppressing thermal shrinkage of the film. By quantitatively analyzing the orientation structure of infrared groups, the minimum structural unit highly associated with CTE was determined. These findings help to deepen our understanding of PI film performance and provide new ideas for studying thermal dimensional stability and draw processing. [ABSTRACT FROM AUTHOR]