Phenylethynyl End‐Capped Fluorinated Imide Oligomer AFR‐PEPA‐N: Morphology and Processibility Characteristics

Abstract

Two phenylethynyl phthalic anhydride‐capped imide oligomers, AFR‐PEPA‐2 and AFR‐PEPA‐8, with molecular weights of 1 601 and 4 699 g · mol−1, respectively, were synthesized and characterized. The AFR‐PEPA‐N oligomers show higher glass transition temperatures and higher thermal decomposition temperatures than phenylethynyl‐terminated imide PETI‐5. After curing for 1 h at 390 °C, AFR‐PEPA‐2 and AFR‐PEPA‐8 have Tgs of 370 and 358 °C, respectively. AFR‐PEPA‐N oligomers demonstrated lower minimum complex melt viscosities than PETI‐5 due to the presence of CF3 group in the backbone structure. 1 601 g · mol−1 AFR‐PEPA‐2 imide oligomer has a complex melt viscosity of 10 Pa · s at 340 °C, and 4 699 g · mol−1 AFR‐PEPA‐8 imide oligomer has a complex melt viscosity of 227 Pa · s at 371 °C. AFR‐PEPA‐N film's crystal morphology was observed using polarized optical microscopy and the AFR‐PEPA‐8 oligomer did not show crystallinity. AFR‐PEPA‐2 film exhibits semicrystalline behavior and the crystallinity does not disappear until the film is cured above 375 °C.

Novel acetylene‐terminated polyisoimides with excellent processability and properties comparison with corresponding polyimides

“…AI‐n0 (repeat unit n = 0) was one component in m ‐AI as shown in GPC curve of Figure 3 and was demonstrated to have crystal phase by XRD in Figure 4. The same phenomenon could be seen for other low‐molecular weight polyimide oligomers 47, 50, 51. After m ‐AI and p ‐AI were cured, m ‐API (cured m ‐AI) and p ‐API (cured p ‐AI) were amorphous as shown in Figure 4.…”

Crystal structure of dimethyl 4-(phenylethynyl)phthalate, C18H14O4

“…To balance the high temperature performance, high hydrolytic resistance and the processing ease of these materials, the exploration of new compositions and new processing methods for polyimides are developing rapidly. Many researchers have demonstrated that termination of various imide oligomers with phenylethynylg roups can lead to dramatic improvements in hydrothermal durability, toughness and processability [3][4][5][6]. The commonly used terminated agent was 4-(phenylethynyl)phthalic anhydride.…”

Blistering in carbon‐fiber‐filled fluorinated polyimide

“…In addition, fiber‐reinforced, high‐temperature, polymer‐matrix composites are particularly attractive for aerospace structures because of their low density [2, 3], high mechanical strength [2, 4–10], high modulus [2, 4, 6, 8, 9], thermo‐oxidative stability [2, 4, 9, 11, 12], electrical properties [2, 6, 10, 13], and excellent chemical resistance [2, 5, 6, 14]. Various polyimide‐based composites have been studied for use in aerospace applications for these reasons [2, 4, 6, 11, 15]. Phenylethynyl‐endcapped fluorinated polyimides are especially useful because of their environmental stability and high glass‐transition temperature ( T g ) (435–455°C) [8].…”

“…Blistering, in particular, occurs when there is enough moisture pressure to exceed the strength of the material, which happens when the temperature and water content is high [6, 17]. In general, polyimides are very thermally stable and have characteristically high T g s and decomposition temperatures [15], but their uptake of moisture needs further study, especially for fluorinated polyimides, because of initial findings with similar polyimides (PMR‐II‐50, AFR700B, and PETI‐5) [3, 16–19]. Adding reinforcements to a neat polyimide resin, such as carbon‐fiber, has been shown to improve the hygrothermal degradation of the composite material [19, 21].…”

“…The blister temperature for both materials at these moisture levels is also low (∼315°C) [3, 6]. Both polyimides exhibit good thermal stability, but the T g for PMR‐II‐50 is 363°C and for AFR700B it is near 400°C, whereas the fluorinated polyimide used here is 435–455°C [5, 8, 15, 23]. Because of the enhanced thermal stability of the fluorinated polyimide, both the neat‐resin and its composites exhibit much better resistance to hygrothermal degradation.…”