Atomistic simulations of phenoxy ring flips in the glassy region of a semicrystalline polyimide

Abstract

AbstractA quasi‐static atomistic simulation methodology is used to study the 180° (π) flip motion of phenoxy rings in the amorphous glass of a semicrystalline polyimide. The π‐flip is carried out for the rings in various local microenvironments in the polymer. Results show that the activation energy distribution for the flip covers a broad range of values. The energetics, short and long scale matrix movements, and the interrelation between cooperativity and polymer structure are also studied. The results are in qualitative agreement with previous simulation and experimental work on other glassy polymers such as bisphenol‐A polycarbonate and polystyrene. The nature of the movement of the amorphous matrix, in response to the ring flip, is far reaching with greater atomic displacements closer to the phenoxy ring. Intermolecular van der Waals and electrostatic interactions contribute significantly to the energy changes associated with the ring flip. Cooperativity is observed for torsion angles along the repeat unit containing the flipped ring. The mean value of the activation energy compares reasonably well to the experimental value for the flip that has been observed previously through solid‐state NMR experiments.