6533b823fe1ef96bd127f380

RESEARCH PRODUCT

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In a new theoretical approach the separation of a pair of chain molecules (measured thermodynamically by the second osmotic virial coefficient A2) is treated as a two-step process: In the first step the molecules are detached from each other by the addition of solvent—keeping their dimensions constant—and in the second step the now isolated coils are allowed to relax into their equilibrium dimensions. For the description of the second step, in which only segments belonging to one molecule take part, an intra-molecular interaction parameter is introduced on the basis of the intrinsic viscosity. The present two-parameter approach yields A2 = A + σ M−(1−a) for the dependence of A2 on the molecular weight M of the polymer; a is the exponent of the Kuhn-Mark-Houwink equation and σ a parameter measuring the effects associated with the second step (becoming zero if the coil dimensions do not depend on polymer concentration). A test of the above relation by means of published material demonstrates its superiority over other two parameter theories: It can describe the actually measured A2(M) well down into the region of oligomers without an additional parameter and it comprises the conceptual advantage of explaining experimental observations concerning ∂A2/∂M > 0 or ∂A2/∂M ≈ 0 for high A2 values.