Effects of chain packing and structural isomerism on the anisotropic linear and volumetric thermal expansion behaviors of polyimide films

Effective Reduction of Volumetric Thermal Expansion of Aromatic Polyimide Films by Incorporating Interchain Crosslinking

“…The linear relationship shown in Figure 8 clearly indicates that P200 is the most significant determining factor for η, and the anisotropy in CTE can be controlled by the in-plane orientations of the PI chains. We have previously reported similar relationships [5,6]. Pottiger et al [24] evaluated the CTE// and CVE values of commercial PI films using TMA measurements and pressure-volume-temperature (PVT) techniques, respectively, where …”

“…Temperature variation over the thickness of the PI films was precisely measured using optical interferometry during the heating process [5,6]. The transmission spectra in the near-IR region were used, owing to the absence of absorptions.…”

“…where ∆n 0 is the intrinsic birefringence estimated by DFT calculations, as reported by Terui et al [13,15] P 200 values were thus estimated according to Equation (6). The coefficient of molecular packing, K p , was estimated according to the following equation:…”

“…However, the D C of approximately 42%-45% should be sufficiently high to fix and immobilize the PI main chains in the solid films. The suppression of local molecular motion, as represented by increased β-and γ-relaxation temperatures, is important to reduce the CVEs of polymers [5,6].…”

“…The relationship between the chemical structure of aromatic PIs and their anisotropic linear and volumetric thermal expansion (VTE) behaviors has been recently characterized [4][5][6]. PIs with bulky side groups, such as -CH 3 and -CF 3 , or those with flexible linkages, such as -O-and -CO-, in the main chain exhibit larger coefficients of volumetric thermal expansion (CVE) compared to PIs containing rigid and linear main chain structures without side groups [4].…”