The accessibility of the fiber to dye is considered to be related to the fraction of the polymer segment which is mobile. This is studied by dyeing the acrylic fiber at temperatures within a 40 degrees C range while treating the samples with different carriers. The relation of the equilibrium dye uptake (dyeability) of the acrylic fiber to the structural parameter, integral(T)(20) (tan delta)(c) dT, with the presence or absence of 20 carrier in solution is linear, confirming the validity of the hypotheses, where (tan delta)(c) is the loss tangent correlated at a temperature of 20 degrees C. Moreover, The effect of carrier to swell the amorphous region of the acrylic fiber was less effective as temperature beyond T-g (mechanical). (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 189-193, 2009