On the expansion of hole in main chain polymers determined by positron annihilation

The temperature dependence of positron annihilation characteristics,₃ andI₃, has been studied on sample of poly(butadiene), poly(isobutylene) and poly(chloroprene). The temperature range was between 15 and 470 K. The rate of expansion of holes or free-volume in all samples was deduced belowT_g as well aboveT_g as appr. 3·10^–3 K^–1 and 2·10^–2 K^–1, respectively. These values are very close to the rate of the mean squared displacement of scatterer<r²>observed in neutron scattering experiments. A possibility to use an inverse value of free-volume,V_f^–1 for study of viscoelastic state of polymers is demonstrated.