Phenylethynyl-terminated oligoimides with ultra-low melt viscosity derived from 1,4-bis(3,4-dicarboxy phenoxy)benzene dianhydride

Abstract

Most of the existing polyimide oligomers for resin transfer molding (RTM) processing exhibited high melt viscosity, which can only maintain below 1 Pa·s at 280°C for 2 h, leading to very high process temperatures. So novel RTM-type oligomers with lower and stable melt viscosities are more desirable. Three series of thermoset oligoimides derived from 1,4-bis(3,4-dicarboxy phenoxy)benzene dianhydride and three different aromatic diamines were prepared herein. The diamines included 4,4′-oxydianiline, 2,2′-bis(trifluoromethyl)benzidine (TFDB), and 2-phenyl-4,4′-diaminodiphenyl ether ( p-ODA). 4-Phenylethynylphthalic anhydride was used as an endcapping reagent. Effects of the chemical structures and molecular weights of the oligoimides on their aggregated structures, melt processability, and the thermal and mechanical properties of the cured films were then systematically investigated. X-Ray diffraction results indicated that ODA series oligoimides and TFDB series oligoimides showed crystallinity in various degrees. However, the asymmetric p-ODA enables the p-ODA series oligoimides to exhibit amorphous forms. It was found that the p-ODA-based oligoimide with a molecular weight of 750 g mol−1 showed very low melt viscosity of 1 Pa·s even at 210°C, and the melt viscosity could maintain below 1 Pa·s after isothermal aging for 2 h at any temperature in the range of 200–280°C by rheological measurements. The cured film also showed a high glass transition temperature of 355°C by dynamic mechanical analysis, very good thermal stability by thermogravimetric analysis, and good mechanical properties. It might be more suitable for RTM processes in the future.

High Thermally Stable and Melt Processable Polyimide Resins Based on Phenylethynyl-Terminated Oligoimides Containing Siloxane Structure

“…Thermosetting polyimide resins have been successfully used as the matrix resin of composites in the manufacture of aviation and aerospace vehicles, owing to their excellent thermal stability, high mechanical properties and good dielectric properties [ 1 , 2 , 3 , 4 ]. However, they are usually difficult to process because of the poor melt fluidity and the volatiles release [ 5 , 6 ]. Therefore, the high temperature and high pressure molding process or vacuum autoclave molding are usually applied for the fabrication of composite parts.…”