The dynamics of a side chain liquid crystal copolymer at two different comp
ositions has been investigated in its smectic A and C phases. J(1) (omega (
0)) and J(2)(2 omega (0)) spectral densities have been determined for aroma
tic deuterium nuclei in the side chains and their interpretation has been c
arried out by means of several available motional models. The dynamic proce
ss mainly contributing to relaxation has been found to be the rotation of t
he phenyl ring about its para-axis, that is best described by a small step
rotational diffusion model, where the diffusion constant has an Arrhenius t
emperature dependence and a Gaussian distribution of the activation energie
s is present, indicating a remarkable degree of dynamic heterogeneity of th
is system. (C) 2001 Elsevier Science BN. All rights reserved.