RELAXATION PROCESSES AND MOLECULAR-MOTION IN A NEW SEMICRYSTALLINE POLYIMIDE

A new polyimide was synthesized from 3,3',4,4'-benzophenonetetracarbox ylic dianhydride (BTDA) and 2,2-dimethyl-1,3-(4-aminophenoxy)propane ( DMDA), and abbreviated to be BTDA-DMDA. This polymer possesses three r elaxation processes which have been observed through dynamic mechanica l and dielectric analyses above -150 degrees C. The a relaxation proce ss has been assigned to be the glass transition and occurs at about 25 0 degrees C with an apparent activation energy of 420 kJ/mol. Two subg lass 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 acti vation energy of 182 kJ/mol and a gamma relaxation process occurs at a round -80 degrees C with an activation energy of 44 kJ/mol. Carbon-13 solid state nuclear magnetic resonance experiments were carried out fo r the study of molecular dynamics at different temperatures. The resul ts indicate that the gamma relaxation is responsible for an oscillatio n 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 aro matic imide rings in the BTDA portion. The molecular motion of the DMD A and BTDA portions are largely decoupled from each other in the frequ ency region studied.