Application of molecular rotors to the determination of the molecular weight dependence of viscosity in polymer melts

Fluorescent molecular rotors, farnesyl-(2-carboxy-2-cyanovinyl)-julolidine (FCVJ), was demonstrated that can be used as an active probe for precise determination of the M dependence of viscosity and the entanglement molecular weight of a polymer by using a molecular weight series of poly(propylene oxide) (PPOX) as model polymers. A scaling behavior consistent with the Rouse model was found on the low molecular weight side. The motion of a chain was restricted by the presence of the topological constraints caused by chain entanglements, and the reptative motion becomes the dominant mode of relaxation. Higher molecular weight PPOX revealed the scaling behavior typical of entangled polymer liquids.