Dynamic Mechanical Analysis and Molecular Mobility of the R-BAPB Type Polyimide

Summary: Dynamic mechanical experiments are performed to study molecular mobility of the R-BAPB type polyimide based on 1,3-bis-(3,3′,4,4′-dicarboxyphenoxy)benzene (R) and 4,4′-bis-(4-aminophenoxy)biphenyl (BAPB) with a molecular weight M_w ∼ 80 000 g/mol. Frequency dependences of the storage and the loss tensile moduli are measured within the temperature domain 199°C ≤ T ≤ 211°C that includes the glass transition temperature of the compound, T_g = 206°C. It is shown that the time-temperature superposition principle holds for the R-BAPB type polyimide. A theoretical analysis of the master curves constructed at T_ref = 204°C is performed on the basis of the piecewise-power-type distribution function of the relaxation times. Relaxation times for typical scales of motion inside polyimide macromolecules are calculated and the molecular weights of the characteristic kinetic units (the Kuhn segment and the chain fragment between entanglements) are estimated.