THERMAL-STABILITY AND THERMAL-EXPANSION STUDIES OF PEEK AND RELATED POLYIMIDES

Thermal stability and thermal expansion properties are reported for se veral high performance polymers which contain carbonyl and/or ether li nking groups designed to increase molecular mobility while retaining h igh temperature properties. The polymers studied include poly(ether et her ketone), PEEK, and three related novel thermoplastic polyimides: N EW-TPI, LARC-CPI, and LARC-IA. Thermogravimetric analysis showed that LARC-CPI exhibited major weight loss by about 450 degrees C, and both PEEK and LARC-CPI lost 50% of their initial weight by 750 degrees C. T hermomechanical analysis (t.m.a.) was used to determine linear coeffic ients of thermal expansion (CTE). All materials showed a large chan tr ansition temperature (T-g). Bulk linear CTEs ranged from 54-70 x 10(-6 ) degrees C-1 below T-g, to 105-200 x 10(-6) degrees C-1 above T-g. Th ese CTEs are larger than those typically observed for more rigid chain polyimides. Using a two-phase model, the amorphous phase CTE was dedu ced for the semicrystalline materials. From t.m.a. data, amorphous pha se CTEs above T-g ranged from 120-245 x 10(-6) degrees C-1. Small angl e X-ray scattering (SAXS) was used to examine changes in long period w ith temperature for PEEK and NEW-TPI. Below T-g, the long period did n ot change much while above T-g, larger increases in the long period we re observed. These increases in the long period with increasing temper ature may be the result either of large amorphous phase expansion, or possibly of melting of thin lamellae. Copyright (C) 1996 Elsevier Scie nce Ltd.