ORGANO-SOLUBLE SEGMENTED RIGID-ROD POLYIMIDE FILMS .5. EFFECT OF ORIENTATION

A series of semi-rigid aromatic polyimides have been synthesized via a one-step polymerization in which the poly(amic acid) precursors were not isolated. The polyimides were synthesized from 3,3',4,4'-biphenylt etracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), an d 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (PFMB) in refluxing m -cresol. Uniaxially oriented films were utilized in order to investiga te the chain orientation in the ordered state. Wide-angle X-ray diffra ction (WAXD) patterns showed an increase in the crystal orientation an d the crystallinity for oriented CPI(100/0) films with increasing draw ratio. Dichroic ratios obtained under polarized Fourier transform inf rared spectroscopy (FTIR) represented overall orientation factors attr ibuted to both ordered and non-ordered regions, and they were a functi on of the incident angle and draw ratio. This indicates that the confo rmational arrangement and chain packing changed during deformation. Th e orientation along the molecular chain axis and the lateral orientati on of the imide planes became increasingly enhanced with increasing dr aw ratio, an indication of planar alignment of the imide planes as wel l as uniaxial orientation of the molecular axis. The surface morpholog y of unoriented and uniaxially oriented films was also studied via tra nsmission electron microscopy (TEM). The lateral crystal dimension of the ordered regions observed from TEM corresponded well to the apparen t crystallite sizes of the (310) crystalline plane in BPDA-PFMB crysta ls obtained from WAXD experiments.