Relaxation processes and molecular motion in a new semicrystalline polyimide

Abstract

AbstractA new polymide 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°C. The α relaxation process has been assigned to be the glass transition and occurs at about 250°C with an apparent activation energy of 420kJ/mol. Two subglass relaxation processes are a β relaxation process at around 100–170°C in a frequency range from 0,1 Hz to 100 kHz with an activation energy of 182 kJ/mol and a γ relaxation process occurs at around −80°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 γ relaxation is responsible for an oscillation and π flipping motion of the two phenoxy rings in the DMDA portion. The β 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 protions are largely decoupled from each other in the frequency region studied.