SMALL CONFORMATIONALLY MOBILE MOLECULES AS PROBES FOR MOLECULAR MOBILITY IN GLASSY-POLYMERS

A new method for studying molecular mobility in glassy polymers-the me thod of conformationally inhomogeneous probes-is described. A small qu antity of a low-molecular-weight compound (probe) having unidentical c onformations with different vibrational spectra is introduced into a p olymer. The thermodynamic and activation parameters responsible for th e concentrations of the conformers and the rates of conformational tra nsitions are connected with both the intramolecular interactions and t he properties of the medium (e.g. polymer). Information about the kine tics and equilibria of the conformers could be obtained by investigati ng the vibrational spectra. This information may be the key to underst anding the molecular mobility and free-volume distribution in polymers . The following compounds were used as probes: 1,2-bromofluoroethane, methyl dichlorophosphate and trans-1,2-dichlorocyclohexane. The polyme rs polystyrene, poly(vinyl chloride), poly(methyl methacrylate), poly( vinyl acetate), poly(vinylbutyral), polypropylene and polybutadiene we re investigated, The temperature dependences of the absorption-band in tensities of the probes were studied. Freezing of the conformational t ransitions in the probe molecules was found at temperatures T(f) chara cterizing specific polymer-probe systems. The T(f) are close to the te mperatures of the relaxation transitions in the pure polymers. The pos sibilities of the method are discussed.