Effect of organoclay on the physical properties of colorless and transparent copoly(amide imide) nanocomposites

Copoly(amic acid) was prepared using the diamine monomer N,N '-[2,2 '-bis(trifluoromethyl)-4,4 '-biphenylene]bis(4-aminobenzamide) (TFAB) and the anhydride monomers 4,4 '-(hexafluoro-isopropylidene)diphthalic anhydride (6FDA) and 4,4 '-biphthalic anhydride (BPA). Thereafter, a colorless and transparent copoly(amide imide) (Co-CPAI) film was synthesized through various heat treatments. Co-CPAI hybrid films with a TFAB : 6FDA : BPA molar ratio of 1 : 0.5 : 0.5 were subsequently fabricated using organically modified hectorite (STN) with various contents ranging from 0 to 7 wt% via the solution intercalation method. Finally, the thermomechanical properties, clay dispersion, and optical transmittance of the hybrid films were investigated. The results of wide-angle X-ray diffractometry and transmission electron microscopy demonstrated good dispersion at low clay loadings; however, clay agglomeration was observed above a certain critical STN content. At the critical STN content of 3 wt%, the clay was evenly distributed in the matrix with a nanoscale thickness of approximately 10 nm. Hybrid films containing 3 wt% STN showed excellent thermomechanical properties. Beyond this critical clay content, the physical properties of the films decreased because of the agglomeration of excess clay. Regardless of the clay content, however, the optical properties of the hybrid films remained constant, and their yellow indices, which ranged from 2 to 4, indicated excellent colorless transparency. Copoly(amic acid) was prepared using the diamine monomer TFAB and the anhydride monomers 6FDA and BPA.