Viscometric test of the theory of K URATA , S TOCKMAYER and R OIG for the expansion of a polymer molecule

Test of the KURATA‐STOCKMAYER‐ROIG (KSR) equation for the linear expansion factor, α of a linear polymer molecule as a function of the molecular weight M was made by evaluating α from the familiar FLORY‐FOX relation α3 = [η]/[η]Θ. The systems chosen are eleven polystyrene fractions in toluene and in methyl ethyl ketone at 34.5°C. and in cyclohexane at 34.5, 45.0, and 55.0°C. It is shown that the KSR equation is well obeyed by the data for the toluene system over a very wide range of molecular weight, while it is valid only for relatively high molecular weights in methyl ethyl ketone and in cyclohexane. In all cases studied, the expansion of the polymer coil due to long‐range interferences between chain elements tends to vanish below a certain chain length which depends on solvent and temperature. Such a critical chain length is abnormally large in the methyl ethyl ketone system, amounting to about 300 monomer units. The reason for this result is not clear to us. Application of the well‐known FLORY equation α5−α3 = CN1/2 to the present data demonstrates its serious limitations.