CRYSTALLIZATION STUDY OF A THERMOPLASTIC POLYIMIDE (NEW-TPI)

Crystallization, melting, and morphology of a thermoplastic polyimide (New-TPI) containing pyromellitic dianhydride (PMDA) and 3,3'-bis (4-aminophenoxy) biphenyl diamine (33BAPB) moieties have been studied. This material showed a glass transition temperature (T(g)) of 250-degrees-C, an equilibrium melting temperature (T(m)o) of 406-degrees-C and a heat of fusion (DELTAH) for 100% crystallinity of 6.38 kJ / mol. Measurements of the crystallization bulk rate (by DSC) and spherulite growth rate (by optical microscopy) indicated that the maximum crystallization temperature was about 320-degrees-C and the crystallization growth process was three-dimensional under thermal nucleation (the Avrami exponent n ca. 4). The rate of nucleation density was estimated to decrease with increasing temperature, and the product of two crystal surface free energies sigma(e)sigma(o) was calculated to be 1176 erg2/cm4. The melt-grown spherulite consistently showed a Maltese cross pattern with negative birefringence under cross-polars. The calculation of polarizability along the three unit cell axes suggested that the crystal b axis may be along the spherulite growth (radial) direction. Two scattering maxima were seen in small-angle x-ray scattering (SAXS) profiles. The dominant peak indicated a long period of ca. 20 nm which varied as a function of crystallization temperature. The weak peak at a d-spacing of 2.5 nm was independent of temperature and has been attributed to the chemical repeat distance determined by Okuyama et al. (indexed as 001). The lamellar thickness l(C), estimated by the correlation function analysis of the SAXS data, was found to be similar to that determined by the Scherrer analysis of the 001 reflection peak. (C) 1994 John Wiley & Sons, Inc.