EN
Temperature dependence of nanoscopic environment of shape memory polymers such as polynorbornene (T_{g}≈313 K), polyurethane (T_{g}≈321 K=dynamic viscoelasticity, destruction of hydrogen bond ≈353 K) and styrene-butadiene copolymer (T_{m}=333 K) is observed in terms of free volume parameters - average size, numerical concentration and size distribution - estimated from positronium lifetime measurement, and mechanisms of their shape recoveries are discussed at a molecular level.