Macromolecular chains obey purely Gaussian statistics close to the theta temperature. An asymptotic regime is also reached far above the theta point. Thermal blob theory permits an approximate calculation of thermal expansion factor. In this theory, an adjustable pa rameter is used as a prefactor (A*N-1) in order to calculate the reduced blob parameter (Nl N-c). In this work, we proposed a different approach to evaluate (A*N-1) by plotting tau M(omega)(1/2)/alpha(eta)(5) against tau M(omega)(1/2). Chain expansion data of poly(4-chlorostyrene) in various solvents is used to evaluate viscosity expansion factors at various temperatures. It seems that predictions of thermal blob theory provide a better fit to experimental points rather than those evaluations based on Flory-type approaches. (C) 1996 John Wiley & Sons, Inc.