Chain connectivity and conformational variability of polymers: Clues to an adequate thermodynamic description of their solutions, 1 - Dilute solutions

This is the first of two parts investigating the Flory-Huggins interaction parameter, chi, as a function of composition and chain length. Part 1 encompasses experimental and theoretical work. The former comprises the synthesis of poly(dimethylsiloxane)s with different molar mass and the measurements of their second osmotic virial coefficients. A(2) in solvents of diverse quality as a function of M via light scattering and osmotic pressures. The theoretical analysis is performed by subdividing the dilution process into two clearly separable steps. It yields the following expression for chi(o), the chi value in range of pair interaction chi(o) = alpha- zetalambda. The parameter alpha measures the effect of contact formation between solvent molecule sand polymer segments at fixed chain conformation, whereas the parameter zeta quantifies the contributions of the conformational changes taking place in response to dilution; zeta becomes zero for theta conditions. The influences of M are exclusively contained in the parameter lambda. The new relation is capable of describing hitherto incomprehensible experimental findings, like a diminution of chio with rising M. The evaluation of experimental information for different systems according to the established equation displays the existence of a linear interrelation between zeta and alpha, 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.