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.