Preparation and Properties of Intrinsically Atomic-Oxygen Resistant Polyimide Films Containing Polyhedral Oligomeric Silsesquioxane (POSS) in the Side Chains

Abstract

The relatively poor atomic-oxygen (AO) resistance of the standard polyimide (PI) films greatly limits the wide applications in low earth orbit (LEO) environments. The introduction of polyhedral oligomeric silsesquioxane (POSS) units into the molecular structures of the PI films has been proven to be an effective procedure for enhancing the AO resistance of the PI films. In the current work, a series of POSS-substituted poly (pyromellitic anhydride-4,4′-oxydianiline) (PMDA-ODA) films (POSS-PI) with different POSS contents were synthesized via a POSS-containing diamine, N-[(heptaisobutyl-POSS)propyl]-3,5-diaminobenzamide (DABA-POSS). Subsequently, the effects of the molecular structures on the thermal, tensile, optical, and especially the AO-erosion behaviors of the POSS-PI films were investigated. The incorporation of the latent POSS substituents decreased the thermal stability and the high-temperature dimensional stability of the pristine PI-0 (PMDA-ODA) film. For instance, the PI-30 film with the DABA-POSS content of 30 wt% in the film exhibited a 5% weight loss temperature (T5%) of 512 °C and a coefficient of linear thermal expansion (CTE) of 54.6 × 10−6/K in the temperature range of 50–250 °C, respectively, which were all inferior to those of the PI-0 film (T5% = 574 °C; CTE = 28.9 × 10−6/K). In addition, the tensile properties of the POSS-containing PI films were also deteriorated, to some extent, due to the incorporation of the DABA-POSS components. The tensile strength (TS) of the POSS-PI films decreased with the order of PI-0 > PI-10 > PI-15 > PI-20 > PI-25 > PI-30, and so did the tensile modulus (TM) and the elongations at break (Eb). PI-30 showed the TS, TM, and Eb values of 75.0 MPa, 1.55 GPa, and 16.1%, respectively, which were all lower than those of the PI-0 film (TS = 131.0 MPa, TM = 1.88 GPa, Eb = 73.2%). Nevertheless, the incorporation of POSS components obviously increased the AO resistance of the PI films. All of the POSS-PI films survived from the AO exposure with the total fluence of 2.16 × 1021 atoms/cm2, while PI-0 was totally eroded under the same circumstance. The PI-30 film showed an AO erosion yield (Es) of 1.1 × 10−25 cm3/atom, which was approximately 3.67% of the PI-0 film (Es = 3.0 × 10−24 cm3/atom). Inert silica or silicate passivation layers were detected on the surface of the POSS-PI films after AO exposure, which efficiently prevented the further erosion of the under-layer materials.

Atomic Oxygen-Resistant Polyimide Composite Films Containing Nanocaged Polyhedral Oligomeric Silsesquioxane Components in Matrix and Fillers

“…The T 5% values of the composite films were about 40 °C higher than those of the pristine films without TSP-POSS additives. For example, POSS-PI-30 film showed a T 5% value of 554 °C, which was 42 °C higher than that of the PI-30 film without TSP-POSS [ 30 ]. Higher silicon contents in the PI composite films afforded much higher char yield of the films at high temperatures.…”

“…In our previous work, it has been found that the introduction of side-chain-substituted POSS units deteriorated the high-temperature dimensional stability of the derived PI films because of the easy movement of the latent POSS groups at elevated temperatures [ 30 ]. In the current work, the addition of TSP-POSS additives further increased the CTE values of the derived PI composite films, which could be deduced from the TMA curves of the films shown in Figure 9 .…”

“…TSP-POSS was obtained from Hybrid Plastics, Co. Ltd., (Hattiesburg, MS, USA). DABA-POSS was prepared according to our previous work [ 30 ]. Pyromellitic dianhydride (PMDA) and 4,4′-Oxydianline (ODA) were purchased from Tokyo Chemical Industry (TCI) Co., Ltd., Tokyo, Japan.…”

“…The AO erosion behaviors of PI composite films were tested in a ground-based AO effect simulation facility [ 30 ]. The AO fluence was measured after exposure by the etch depth of Kapton ® reference sample, whose erosion yield ( E Kapton ) was 3.0 × 10 −24 cm 3 /atom.…”

“…In our previous work, the effects of the side-chain substituted POSS units on the optical, thermal, mechanical, and AO erosion behaviors of PI (PMDA-ODA) films were systemically reported [ 30 ]. In the current work, the POSS units were endeavored to incorporate into the PI (PMDA-ODA) films via the combination of copolymerization and physical blending procedures.…”