Molecular dynamics of poly(propylene oxide-co-glycidyl methyl ether) (GME): Unraveling the effect of composition and molecular weight on segmental and chain dynamics

In this study, the segmental and normal mode dynamics of polar aliphatic polyethers based on the copolymerization of propylene oxide (PO) and glycidyl methyl ether (GME) were investigated using dielectric spectroscopy for a wide range of molecular weights and monomers compositions. Polar interaction of glycidyl methyl ether results in increasing glass transition temperature (T_g) and slowing down the segmental dynamics. However, the fragility of the copolymers is identical to the neat poly (propylene oxide) which implies that the influence of the backbone structure is dominant rather than the molecular cohesive energy factor on the fragility. In addition, the temperature dependence of the normal mode is weaker than segmental dynamics which resulted in the decoupling of segmental and normal mode dynamics. The effect of molecular weight on the decoupling is prominent in comparison to the copolymer composition. From the relaxation strength of the normal mode and segmental mode, the parallel and perpendicular components of the dipole moment were calculated. The effect of glycidyl methyl ether (GME) composition on the dielectric strength is significant due to the higher dipole moment of GME. The results of the current work shed light on the effect of cohesive energy density and molecular weight on the segmental and chain dynamics of polymers.