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RESEARCH PRODUCT

Chain Connectivity and Conformational Variability of Polymers: Clues to an Adequate Thermodynamic Description of Their Solutions, 1

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This is the first of two parts investigating the Flory-Huggins interaction parameter, χ, as a function of composition and chain length. Part 1 encompasses experimental and theorical work. The former comprise the synthesis of poly(dimethylsiloxane)s with different molar mass and the measurements of their second second osmotic virial coefficients, A 2 , in solvents of diverse quality as a function of M via light scattering and osmotic pressures. The theorical analysis is performed by subdividing the dilution process into two clearly separable steps. It yields the following expression for χ ο , the χ value in range of pair interaction : χ ο = α - ζ λ. The parameter α measures the effect of contact formation between solvent molecules and polymer segments at fixed chain conformation, whereas the parameter ζ quantifies the contributions of the conformational changes taking place in response to dilution; ζ becomes zero for theta conditions. The influences of M are exclusively contained in the parameter λ . The new relation is capable of describingt hitherto incomprehensible experimental findings, like a diminution of χ ο with rising M. The evaluation of experimental information for different systems according to the established equation displays the existence of a linear interrelation between ζ and α. Part 2 of this investigation presents the generalization of the present approach to solutions of arbitrary composition and discusses the physical meaning of the parameters in more detail