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-a minophenoxy) biphenyl diamine (33BAPB) moieties have been studied. Thi s 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. Measu rements of the crystallization bulk rate (by DSC) and spherulite growt h rate (by optical microscopy) indicated that the maximum crystallizat ion temperature was about 320-degrees-C and the crystallization growth process was three-dimensional under thermal nucleation (the Avrami ex ponent n ca. 4). The rate of nucleation density was estimated to decre ase with increasing temperature, and the product of two crystal surfac e free energies sigma(e)sigma(o) was calculated to be 1176 erg2/cm4. T he melt-grown spherulite consistently showed a Maltese cross pattern w ith negative birefringence under cross-polars. The calculation of pola rizability along the three unit cell axes suggested that the crystal b axis may be along the spherulite growth (radial) direction. Two scatt ering 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-spa cing 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 fun ction analysis of the SAXS data, was found to be similar to that deter mined by the Scherrer analysis of the 001 reflection peak. (C) 1994 Jo hn Wiley & Sons, Inc.