Non-Theta Conditions and the Mark-Houwink-Sakurada Equation

4 Non-Theta Conditions and the Mark-Houwink-Sakurada Equation 

For a solution not in its theta state, the volume pervaded by a polymer molecule is greater than that assumed in the above discussion, and in place of Eq. 2.88, the empirical Mark-Houwink-Sakurada (MHS) equation is used  

A method for correcting intrinsic viscosity data for small departures from the theta state to determine Xg was proposed by Bmchard [ 49 ] and by Stockmayer and Fixman [ 50 ]. While the model on which this method is based is no longer thought to be valid, the equation that results, the BSF equation, has been found useful for dealing with small deviations from theta conditions. The BSF equation is shown here as Eq. 2.91  

This implies that Kg can be determined as the intercept of a plot of [J7]M versus 

Fetters etal. [19] tabulated data from many sources for five polymers that have been studied using nearly monodisperse samples at theta or near-theta conditions. Four of the polymers, 1,4-polybutadiene, 1,4-polyisoprene, polystyrene and poly(a-methylstyrene), were prepared by means of anionic polymerization, while the fifth, polyisobutylene, was a nearly monodisperse sample obtained by fractionation. They foimd that the data for twelve samples of 1,4-poly-butadiene in dioxane at 26.5 °C could be fitted by the MHS Eq. 2.90 as shown below  

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