The Yamakawa-Fuji theory and several form of Bohdanecký “worm-like” relationship which has been derived from Yamakawa-Fuji theory has been applied to dilute solution viscosity and molar mass data of poly(2,6-diisopropylphenyl methacrylate) (PDP) to estimate the conformational flexibility/rigidity of PDP in single solvents and a mixed binary to determine whether the unperturbed state depends on medium or the model. Two type of extrapolation has been applied to the intrinsic viscosity of PDP in toluene, tetrahydrofuran, and a critical-mixture of tetrahydrofuran/water to estimate the length of Kuhn statistical segment which is a measure of equilibrium rigidity of a polymeric chain, the end-to-end distance, the cross-section diameter, and the shift factor. The length of Kuhn statistical segment of PDP is found to be more solvent dependent rather than the model; it is larger than poly(methyl methacrylate), and poly(phenyl methacrylate) and considerably smaller than cellulose derivatives whose chains are known to possess greater equilibrium rigidity. The molecular parameters indicate the PDP has a particular conformational property: it is random flight in mixed critical solvent TWi, and it is semi rigid in better solvents such as THF and toluene.