Free volume microstructure of amorphous polymers at glass transition temperatures from positron annihilation spectroscopy data

The analysis of annihilation characteristics of ortho-positronium at conventional calorimetric glass transition temperatures for a series of amorphous polymers reveals empirical correlations of average lifetime of o-Ps <(tau)over bar>(3g), and of its product with a relative intensity I-3g with appropriate T-g(DSC) values. These trends in terms of free volume mean that both the average size of free volume hole entity <(nu)over bar>(hg) and the fractional free volume grow with increasing T-g(DSC). The results are discussed considering the chemical microstructure as well as possible mechanisms acting in glass transition. A relation is indicated between geometric and flexibility characteristics of chains and the <(nu)over bar>(hg) and f(g) parameters of free volume microstructure on the one side and potential motional processes responsible for solidification of the amorphous system on the other side.