Precise Analysis of Thermal Volume Expansion of Crystal Lattice for Fully Aromatic Crystalline Polyimides by X-ray Diffraction Method: Relationship between Molecular Structure and Linear/Volumetric Thermal Expansion

Abstract

Coefficients of thermal linear and volumetric expansion (CTE, CVE) of crystal lattice for 13 fully aromatic crystalline polyimides (PIs) were evaluated from lattice parameters measured from variable-temperature (VT) synchrotron X-ray diffraction patterns, and the effects of chemical structure on CTE and CVE are discussed. The smallest CVE (116 ppm K–1) was observed for PMDA-PPD with the simplest rigid-rod structure, and the largest CTE anisotropy was observed for PMDA-ODA containing an ether linkage with an extraordinarily negative CTE a (−44 ppm K–1). The values and anisotropy of the CTEs strongly depended on the crystalline structure, whereas the CVEs were negatively correlated with the weight density, regardless of the PI type. The correlation was explained using the Grüneisen equation, (∂V/∂T) P /V = γC v,interχ, assuming that isothermal compressibility χ dominates the equation. An increase in the weight density and/or molecular weight of repeating units effectively suppresses the CVEs of crystalline PIs.

Exerting Additive‐Assisted Morphological Control during Hydrothermal Polymerization

“…PPPI was the first example of a fully crystalline polyimide obtained by HTP . By HTP, but also by other routes, PPPI is obtained as highly crystalline powder typically composed of microflower morphologies. In the first publication on PPPI from HTP, we proposed a hypothesis for the arising morphologies, which consists of a monomer salt dissolution–polymerization–crystallization sequence that repeats several times .…”

Preparation and Properties of Rigid Polyimides from Dianhydrides Having Various Number of Phenylene Units and <i>p</i>-Phenylenediamine

“…Diffraction peaks were not observed in PI-PP-m (m = 0, 1, 2, 3), which tended to be amorphous in nature. The structure of PI-PP-0 is the same as that of Upilex-S type polyimides which are known as crystalline polyimides [16][17][18]. The crystallinity may depend on the synthetic method of the polyimide, and heat treatment of Upilex-S type polyimide films was carried out by stepwise heating up to 400 o C [17].…”

Anisotropic Linear and Volumetric Thermal‐Expansion Behaviors of Self‐Standing Polyimide Films Analyzed by Thermomechanical Analysis (TMA) and Optical Interferometry

“…Interestingly, s ‐BPDA–DATP with a rectilinear p ‐terphenyl structure exhibited a much smaller K p (0.596) than s ‐BPDA–PPD, which could have been the result of an enlarged free volume and the enhanced local rotational motion along the terphenyl moiety. This is supported by the thermal‐expansion behavior of the crystal lattice of s ‐BPDA–DATP . For the PMDA–PIs, it should be noted that PMDA–DCHM, which possesses two cyclohexyl rings with a bent CH 2  linkage, exhibited a large K p (0.635) compared with the PIs with linear structures (0.603–0.613).…”

“…The linear relationship between η and P 200 in Figure also indicates that the anisotropy in thermal expansion could be effectively enhanced by increasing the in‐plane orientation of PI chains. When the PI chains were perfectly oriented in the film plane, the volumetric expansion should dominated by the out‐of‐plane expansion, i.e ., β ≈ α ⊥ because the CTE along the c ‐axis (chain axis) of PI chains has been reported to be very small (≈8 ppm K −1 ) or negative . Therefore, when the P 200 values approached −0.5, it is reasonable for η values to become close to unity, such that β was nearly equal to α ⊥ , and α // was almost null.…”