Abstract

The effects of melt time and temperature as well as crystallization temperature on spherulitic growth rate and morphology were determined for a new semicrystalline polyimide based on 1,3-bis (4-aminophenoxy) benzene and 3,3',4,4'-benzophenonetetracarboxylic dianhydride. Experiments were run on thin films (ca. 1 mils) and thick films (ca. 2 mils). The data show that in the temperature range of 340 &endash; 380°C nucleation density increases as crystallization temperature decreases. The nucleation density decreases however when melt time and temperature are increased. Differential Scanning Calorimetry (DSC) was utilized to determine the thermal stability and recrystallizability after elevated times and temperatures in the melt. DSC revealed that the material had a glass transition of ca. 230°C and two distinct melting transitions at 350°C and ca. 412°C. It was found that the lower melting point and associated heat of fusion (DHf1) remained relatively stable after elevated melt times and temperatures until the harshest melting conditions (460°C, 30 mins) were realized. The higher melting point and associated heat of fusion (DHf2) were much less stable even at milder melting conditions. This indicated that the development of the higher melting crystalline phase was more sensitive to melt time and temperature than the lower melting phase. Structural analyses including Atomic Force Microscopy (AFM) and Small Angle X-ray Scattering (SAXS, data not presented) suggest the morphology is of a folded lamellar structure. Dynamic Mechanical Analysis (DMA) was conducted on various samples of this material that had been annealed at different temperatures from an amorphous state. The data indicate that milder annealing conditions (300°C, 2 hours) produce less crystallinity than annealing at higher temperatures. Also, the modulus of this material remains relatively high well above the glass transition temperature due to the presence of crystallinity.

Back to the 1998 Participants and Abstracts Index