THERMAL-EXPANSION OF THE CRYSTAL-LATTICE OF NOVEL THERMOPLASTIC POLYIMIDES

Measurements of the coefficient of thermal expansion (CTE) of the crys talline lattice of two semicrystalline thermoplastic polyimides are re ported. NEW-TPI and LARC-CPI polyimides were studied using elevated te mperature wide-angle x-ray scattering (WAXS) from 25 degrees C to 325 degrees C. To examine possible shifts in the c-axis, a novel approach developed in our lab was used to create highly oriented samples. Films were treated in 1-methyl-2-pyrrolidinone (NMP) at the reflux temperat ure, washed and then dried under constraint. The films treated in this manner were highly oriented, with c-axes preferentially aligned along the film normal. The advantage of this orientation is that it allows numerous reflections of type (00l) to be examined for temperature shif ts of the c-axis using reflection mode WAXS. No systematic shift of th e c-axis lattice parameter as a function of temperature was observed i n either NEW-TPI or LARC-CPI. The c-axis thermal expansion is conclude d to be smaller than 8 X 10(-6)/degrees C for LARC-CPI, and for NEW-TP I may be weakly negative, From WAXS of unoriented films, systematic sh ifts in the a and b lattice parameters were deduced as a function of t emperature. The linear CTEs relating these unit cell parameters at tem perature T to their values at 0 degrees C are: [GRAPHICS] (C) 1995 Joh n Wiley and Sons, Inc.