RELAXATION PROCESSES AND MOLECULAR-MOTION IN A NEW SEMICRYSTALLINE POLYIMIDE

A new polyimide was synthesized from 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and 2,2-dimethyl-1,3-(4-aminophenoxy)propane (DMDA), and abbreviated to be BTDA-DMDA. This polymer possesses three relaxation processes which have been observed through dynamic mechanical and dielectric analyses above -150 degrees C. The a relaxation process has been assigned to be the glass transition and occurs at about 250 degrees C with an apparent activation energy of 420 kJ/mol. Two subglass relaxation processes are a beta relaxation process at around 100-170 degrees C in a frequency range from 0,1 Hz to 100 kHz with an activation energy of 182 kJ/mol and a gamma relaxation process occurs at around -80 degrees C with an activation energy of 44 kJ/mol. Carbon-13 solid state nuclear magnetic resonance experiments were carried out for the study of molecular dynamics at different temperatures. The results indicate that the gamma relaxation is responsible for an oscillation and pi flipping motion of the two phenoxy rings in the DMDA portion. The beta relaxation was shown to pertain to the kHz-motion of the aromatic imide rings in the BTDA portion. The molecular motion of the DMDA and BTDA portions are largely decoupled from each other in the frequency region studied.