Synthesis and liquid‐crystal‐aligning properties of novel aromatic poly(amide imide)s bearing n ‐alkyloxy side chains

Novel aromatic poly(amide imide)s ( m ‐PAIs, m = 8, 12, 16) containing preformed isophthalamide unit and pendent n ‐alkyloxy (‐O‐ n ‐C m H 2 m +1 , m = 8, 12, 16) side chains were prepared in thin films by polymerization of pyromellitic dianhydride (PMDA) with N,N ′‐bis(4‐aminophenyl)‐5‐( n ‐alkyloxy)isophthalamides ( m ‐DAs) obtained from N,N ′‐bis(4‐nitrophenyl)‐5‐( n ‐alkyloxy)isophthalamides ( m ‐DNs). The m ‐PAI films were tough, flexible and transparent with inherent viscosities in the 1.25–1.67 dL/g range in DMAc and soluble in DMAc and NMP on heating. In TGA m ‐PAIs began to degrade around 440°C and in DSC no phase transitions were detected. In X‐ray diffractometry the m ‐PAIs appeared amorphous with loosely developed layered crystalline structure. In liquid crystal (LC)‐aligning performance measured using 4‐ n ‐pentyl‐4′‐cyanobiphenyl (5CB) on thin film surfaces rubbed with standard velvet fibers, the m ‐PAIs showed homogeneous LC alignment parallel to the rubbing direction with 2.5–17.5° pretilt angles, depending on the rubbing density and n ‐alkyloxy side chain length. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007