Hideki Ozawa

Molecular Design of Heat Resistant Polyimides Having Excellent Processability and High Glass Transition Temperature

The relationship between the imide structures and morphology are discussed in order to develop heat resistant polyimides having excellent processability and toughness. Addition-type imide oligomers consisting of asymmetric 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA) and 3,4′-oxydianiline (3,4′-ODA) and/or 4,4′-oxydianiline (4,4′-ODA) with 4-phenylethynyl phthalic anhydride (PEPA) were synthesized and characterized. The imide oligomers derived from 3,4′-ODA; 4,4′-ODA (50:50) comonomer having molecular weights of 5240 g mol−1 (Oligo-10) and 1340 g mol−1 (Oligo-1.5) showed good solubility in aprotic solvents such as DMAc and NMP, and were successfully cured at 370°C for one hour. The thermal curing process, and thermal and rheological properties of the imide oligomers were investigated by FT-IR, differential scanning calorimetry, thermogravimetric analysis, and dynamic rheometry. It was observed that the melt flow dramatically decreased above the T g for Oligo-1.5, resulting in a viscosity as low as 200 Poise at 300°C. Whereas, a melt viscosity for Oligo-10 was 20 000 Poise at 365°C. The glass transition temperatures of these cured oligomers were 341°C and 308°C, respectively. In addition to the excellent melt property, the cured oligomers exhibited good thermo-oxidative stability. Furthermore, the cured imide oligomer consisting of a-BPDA and 4,4′-ODA with PEPA (Oligo-4.5) exhibited over 13% flexural elongation and a T g of 343°C. Their T-300 carbon fibre composites were also well consolidated demonstrating excellent processability and properties. It is concluded that amorphous, aromatic imide structures without any weak linkages such as alkyl and methylene groups are very effective in the molecular design of heat resistant, addition-type polyimides. The excellent properties exhibited in a-BPDA based polyimides demonstrate a promising potential for future aerospace applications.

Processing and properties of carbon fiber reinforced triple-A polyimide (Tri-A PI) matrix composites

This paper presents experimental results for the processing and mechanical properties of carbon fiber reinforced composites of a newly developed amorphous, asymmetric, and addition type polyimide (Triple-A PI). The imide oligomers were synthesized from the reaction of 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA), 4,4′-oxydiaminine (ODA), and phenylethynyl phthalic anhydride (PEPA). Because of amorphous structure, the melting point and melt viscosities of the polymer are relatively lower as compared with similar polyimides such as LaRC™ PETI-5. In spite of the lower molecular weight of the imide oligomer (<2500 g/mol), the cured polymer exhibits excellent mechanical properties because of the irregular and asymmetric structure as well as flexible end-capper. Carbon fiber reinforced composites were fabricated by routing prepreg consolidation. The composites exhibit excellent mechanical properties with high glass transition temperature (>320°C).

Development of a Cure/Postcure Cycle for PETI-330 Laminates Fabricated by Resin Transfer Molding

As part of our product development effort for PETI-330, an investigation to determine the effect of a thermal cure cycle and thermal postcure treatment on laminate properties was conducted. Laminates of PETI-330/T650-35 carbon fabric (un-sized) were fabricated by resin transfer molding (RTM) using a high temperature injector. The resin was degassed at 525-550 °F (274-288 °C) and subsequently injected into an Invar tool and cured for 1 h at 700 °F(371 °C). The laminates were characterized for quality by ultrasonic inspection and acid digestion, the dry glass transition temperatures (Tg values) were determined by dynamic mechanical thermal analysis (DMTA). Specimens (7.6 cm × 7.6 cm) were subsequently machined from the panels and free-standing postcures were performed at 600 °F(316 °C), 625 °F (329 °C), 675 °F (357 °C) and 700 °F(371 °C) for 6 and 12 h at each temperature in flowing air at 1 atmosphere. The postcured specimens were characterized for weight loss, and dry and wet Tg values. The postcured laminates were machined into specimens approximately 7.6 cm × 6.4 cm and isothermal aging was performed for 100 h at 625 °F (329 °C), 650 °F(343 °C) and 700 °F(371 °C). After isothermal aging, the aged specimens were characterized for weight loss, dry and wet Tg and micro-cracking using optical microscopy. The results of this study are presented. Based on these results, the postcure conditions that gave the best combination of results were identified.