The absolute free-volume fraction in polymers from positron lifetime measurements

The summary of annihilation experiments of 6 simple elastomers in wide temperature interval of (15 - 370) K is presented. It is shown that combined use of positron annihilation lifetime spectroscopy (PAL) and dilatometry (specific volume measurement) provides the temperature dependence of absolute value of fraction of free volume f (T) and a unique information on thermal expansion coefficient of occupied volume α0. The proposed model allows the determination of absolute value of occupied volume V0. In the case of poly(isobutylene) and cis-trans 1,4 poly(butadiene) results from PAL are compared with that obtained from the viscosity and the temperature shift parameter measurements. This comparison indicates that the positron annihilation reflects the same basic mechanism as the viscosity and relaxation processes. (orig.)