We present a combined study of the rotational dynamics and free volume in a series of 1,4 -poly(isoprene)s using ESR and PALS, respectively. The spectral parameter of mobility of the spin probe TEMPO is related to the annihilation of the ortho-positronium (o-Ps) probe. The o-Ps lifetime rules are valid independent of chain length and moreover, the T coincides with the bend effect at Tb1L. Finally, the new finding is that the first acceleration at Tx1 slow agrees with a change in the o-Ps lifetime width parameter below the glass transition temperature.