Abstract: The relaxation of polystyrene (PS) chains with different molecular weights and concentrations and at different temperatures have been studied in detail. Cyclohexane and 1,4-dioxane were used as the theta solvent and as good solvent respectively. It was found that the topological and cohesional entanglements exist simultaniously in polystyrene solutions. The former depends strongly on molecular weight, concentration and temperature, and the latter depends mainly on concentration and temperature.The interlocking structure of the side chain-aromatic rings (i. e. cohesional entanglement) has a great effect on the dissolution process and main chain motion of polystyrene, thus it determines the solution property and even the property of PS bulk. In addtion, chain molecular weights in different ranges in values have quite dif ferent effects on the relaxation of PS. This behaviour is related to the formation of PS chain entanglements in solutions, and the number of entanglement points in a unit volume.

Key words: NMR, Relaxation, Cohesional entanglement, Polystyrene