Abstract: The paper reports the concentration and temperature dependence on diffusion coefficients for 4-arm star polystyrene in a good and a 0 solvents (THF and CH)studied by cumulent method. In₀solvent, when T>0 or T<0, the molecular diffusion behaves as in a good solvent and a poor solvent. Extrapolating concentration to zero, we obtained the molecular diffusion coefficients at infinite dilution at various temperatures. With Stokes-Einstein equation, we gave the hydrodynamic radii of 4-arm star polystyrene in different solvents. InDwas plotted against 1/T, we got the values of diffusion activation energy E_n^THF=7. 07 kJ/mol, E_n^CH=14. 06 kJ/mol, for 4-arm star polystyrene in THFand CHrespectively.

Key words: Photon correlation spectroscopy, Star polymer, Molecular diffusion