Miscibility, Structure, and Property of Poly(biphenyl dianhydride perfluoromethylbenzidine)—Poly(ether imide) Molecular Composites

Abstract

Miscibility of segmented rigid-rod polyimide (PI), viz., biphenyl dianhydride perfluoromethylbenzidine (BPDA-PFMB), and flexible polyether imide (PEI) molecular composites was established by differential scanning calorimetry. The composite films of BPDA -PFMB/PEI were drawn at elevated temperatures above their glass transitions. Tensile moduli of the films were evaluated as a function of composition and draw ratio. Molecular orientations of polyimide were determined by birefringence and wide-angle X-ray diffraction. The crystal orientation behavior of the 80/20 BPDA-PFMB/PEI was analyzed in the framework of the affine deformation model.Recently, various types of rigid-rod polyimide (PI) derivatives and polyether imide (PEI) molecular composites were found to be completely miscible QJ. This miscibility has been ascribed to similarity of the imide structure between PI and PEI. The tensile modulus and strength of bulk molecular composites showed remarkable improvement with increase of the polyimide content. Although the molecular reinforcement of the flexible PEI matrix via incorporation of the PI rigid-rod molecules appears unequivocal, the molecular weight of the above rigid-rod polyimide derivatives was rather low as exemplified by their low inherent viscosity (2.2-2.63 dl/g ) (1). Such low molecular weight systems tend to favor miscibility. Hence, we have selected a segmented rigid-rod polyimide, viz., biphenyldianhydride perfluoromethylbenzidine (BPDA-PFMB) having a higher molecular weight, (i.e., inherent viscosity of 4.9 dl/g) and a high aspect ratio to ascertain the concept of molecular composites. It is promising to achieve true miscibility between the segmented rigid-rod BPDA-PFMB and the flexible PEI because of their similar imide structure.The highly drawn rigid-rod polymers generally show extremely high modulus and high strength close to their theoretical values. However, the compressive strength of these rigid materials is rather poor, thereby prohibiting their applications as a