The effect of molecular weight on frictional coefficients of poly‐α‐methylstyrene

The frictional coefficients. [f] of a wide range of poly‐α‐methylstyrene samples ranging in molecular weight from dimer to polymers of M ∼ 106 have been measured in a good solvent (toluene) and under θ conditions (cyclohexane, 37°C). All products were prepared anionically, and the very low molecular weight samples were initiated with phenyl‐isopropyl potassium to ensure that the end‐groups were not significantly different from the polymer chain. [f] was measured using both diffusion and sedimentation techniques. At molecular weights below ∼ 104, [f] is independent of solvent and proportional to M0.5 to quite low molecular weight. Divergences only occur at the very lowest part of the range. Above M∼ 104, [f] continues to be proportional to M0.5 in cyclohexane as expected, but the values in toluene become greater because of greater chain expansion in the better solvent. The results are discussed in terms of current theories of conformations of polymers in solution and its effect on flow properties.