@@According to de Genne's classification [ 1 ], polymer solution ought be divided into three regimes, namely dilute, semi-dilute and concentrated solutions. The boundary concentration between the dilute and the semi-dilute solution is named overlap concentration C*, at which the individual coil just in contact with surrounding coils statically. In 1982, Prof. Qian Renyuan [2, 3] proposed that the dilute solution should be subdivided into two subregimes i.e., extremely dilute and dilute solution. He introduced a technical term dynamic contact concentration and symbol Cs for the boundary between these two sub-regimes. The symbol Cs means the macromolecular coil in solution starts to shrink when c>Cs. The existence of dynamic contact concentration was confirmed later by size exclusion chromatography [4], Dynamic light scattering measurements of polystyrene solution [5] and physical gel formation of polymer solution [6].
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