CHARACTERIZATION OF THE SOLID-STATE PROPERTIES OF POLY(AMIDE IMIDE)S

Thin films of poly(amide imide)s (PAIs) from dichloro-dianhydrides of trimellitimide- and/or pyromellitimide-N-acetic acids (TMI and PMI), l inear aromatic diamines (LADs), and/or cardo-9,9'-bis-phenylfluorene d iamine (CDA) cast from solutions in dimethyl acetamide were characteri zed by wide-angle and small-angle X-ray diffraction (WAXS and SAXS), d ynamic mechanical analysis (DMA), and broad-band dielectric relaxation spectroscopy (DRS). The main experimental results may be summarized a s follows. (i) The SAXS patterns of all the PAIs were indicative of th e absence of large-scale structural heterogeneity; however, the asymme tricity of the profiles of essentially amorphous halos in the WAXS pic tures suggested the possibility of a weak paracrystalline order. (ii) The glass transition temperatures, T-g, tended to increase linearly wi th the product of chain persistence length by chain cross-sectional ar ea, from 520-540 K for PAI(TMI/LAD) to 625 K for PAI(PMI/CDA) and to 6 45 K for PAI(TMI/CDA). (iii) In the temperature interval 170-470 K, th e dielectric permittivity for the majority of the PAIs increased by a factor of 1.5 (from around 4 at 170 K). (iv) The structure-invariant l ow-temperature gamma-relaxation around 225 K (1 kHz) with an apparent activation enthalpy of about 50 kJ/mol (DRS) was tentatively attribute d to the non-cooperative, local mobility of imide cycles. (v) alpha'-R elaxations and T(g)s were attributed to the onset of cooperative segme ntal motions in loosely packed and in densely packed micro-regions, re spectively.