DEVELOPMENT OF CRYSTALLINITY IN NEW-TPI POLYIMIDE

Development of crystallinity in NEW-TPI semicrystalline polyimide has been studied using differential scanning calorimetry (DSC), wide (WAXS ), and small angle X-ray scattering (SAXS). Crystallinity of the fully imidized powder, pellet. or film processed NEW-TPI can occur from the melt, and depends upon the holding temperature of the melt. Repetitiv e exposure to elevated temperatures supresses the development of cryst allinity from the melt state. In amorphous pellets and film, crystalli nity can also develop by cold crystallization from the rubbery amorpho us state. SAXS results show that during cold crystallization, NEW-TPI develops a periodic structure consistent with formation of alternating crystal-amorphous stacks, but with crystals only a few molecular repe at units thick. Kinetics of nonisothermal crystallization were studied as a function of heating rate and could be described using the Ozawa analysis. Non-isothermal crystallization proceeds at a slower rate in NEW-TPI than in other high temperature thermoplastics such as PEEK, an d with a much narrower processing window. The maximum degree of crysta llinity that could develop during heating was 0.34, which occurred at a rate of 5-degrees-C/min. Similar degrees of crystallinity could be i ntroduced by heating amorphous NEW-TPI film in N-methylpyrrolidone.