Hybrid inorganic/organic polymers have been prepared by copolymerizing a polyimide having the same chemical repeat unit as Kapton with an open-cage polyhedral oligomeric silsesquioxane (POSS). These POSS/polyimide hybrid polymers are Kapton-like polymers containing POSS nanoparticles that are chemically bound into the polymer chain. Samples of these POSS polyimides, as well as polyimide controls, have been exposed to a hyperthermal 0-atom beam that is produced by a laser-detonation source. Exposed and unexposed surfaces have been characterized by surface profilometry, atomic force microscopy, and X-ray photoelectron spectroscopy The data indicate that the POSS-containing polyimides have significantly lower erosion yields than Kapton, because they form a surface SiO2 layer which passivates the surface and protects the underlying polymer from further 0-atom attack. These results suggest promise for the use of a POSS polyimide polymer as a "drop-in" replacement for Kapton on spacecraft operating in the low-Earth orbital environment.
Poly(ethylene terephthalate) (PET)-based composite fibers were prepared by melt spinning three types of PET/polyhedral oligomeric silsesquioxane (POSS) composites. These composites were made by either melt blending POSS with PET at 5 wt% loading level (non-reactive POSS and silanol POSS) or by in-situ polymerization with 2.5 wt% reactive POSS. Significant increases in tensile modulus and tensile strengths were achieved in PET fibers with non-reactive POSS at room temperature. The hightemperature modulus retention was found to be much better for PET/silanol POSS fiber when compared to that of control PET. Although other PET/POSS nancomposite fibers tested did not show this high retention of modulus at elevated temperatures, PET/isooctylPOSS nanocomposite fibers did show increased modulus at elevated temperature compared to that of PET. Higher compressive strengths, compared to PET fibers, were observed for all three nanocomposite fibers. Gel permeation chromatography measurement suggested that there is no significant change in molecular weight during preparation of PET/POSS nanocomposites. SEM observations suggest that there is no obvious phase separation in any of the three PET/POSS systems. Crystallization behavior and thermal stability of the composite were also studied. The fiber spinning and mechanical performance with 10 and 20 wt% of trisilanolisooctyl POSS2 were also investigated1 the composites with higher concentrations of this nanofiller can be spun without any difficulty. At room temperature, the fiber tensile modulus increased steadily with the POSS concentration while fiber tensile strength showed no significant change. The elongation at break decreased significantly with increasing of POSS concentration. The high-temperature moduli of PET/POSS nanocomposite fibers were found to be rather variable, likely due to the modest compatibility between filler and polymers, which can lead to structural anisotropy within the composite.
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