Residual stress behavior and physical properties of colorless and transparent polyimide films

A series of polyimide (PI) was prepared by reacting 4,4'-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA) as the anhydride and bis(3-aminophenyl) sulfone (APS), bis[4-(3-aminophenoxy)-phenyl] sulfone (BAPS), 2,2-bis(4-aminophenyl)-hexafluoropropane (6FPD), 2,2-bis[4-(4-aminophenoxy)-phenyl]hexafluoropropane (6FBAPP), 2,2'-bis(trifluorornethyl)benzidine (TFDB), or 1,4-phenyIenediamine (PDA) as the diamine. Residual stress behaviors were detected in-situ during thermal imidization of the polyimide precursors using a thin film stress analyzer (TFSA), and interpreted with respect to their morphology. According to the molecular orientation and packing order, the residual stress varied from 23.1 to 12.5 MPa, decreased with increasing chain rigidity. The thermal properties of the PI films were investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and thermomechanical analysis (TMA). Their optical properties were measured by ultraviolet-visible spectrophotometer (UV-vis), and spectrophotometry. The properties of PI films were found to be strongly dependent upon the morphological structure. However, trade-offs between residual stress and optical properties were identified.