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, 2A(zz), of the spin probe TEMPO is related to the annihilation of the ortho-positronium (o-Ps) probe. The o-Ps lifetime tau(3)(T-50G) congruent to const. 1 and tau(3)(T-x1(fast)) congruent to const. 2 rules are valid independent of chain length and moreover, the T-50G's coincides with the bend effect at T-b1(L)'s. Finally, the new finding is that the first acceleration at T-x1(slow) agrees with a change in the o-Ps lifetime width parameter, sigma(3), below the glass transition temperature. (C) 2014 Elsevier B.V. All rights reserved.