Determination of number‐average and weight‐average molecular weights of polymer sample from diffusion and sedimentation velocity measurements in theta solvent

摘要

AbstractSeveral methods to determine number‐average molecular weightMnand weight‐average molecular weightMw, of a polymer sample are proposed from diffusion and sedimentation velocity measurements at the θ point. According to these methods,MnandMware determined from the diffusion constant vs. molecular weight relationship, and also from the equations of Svedberg and Flory–Mandelkern, using the 2nd‐order and the –2nd‐order diffusion constants. These methods have been applied to four samples of polydisperse polystyrene in the θ solvent, cyclohexane at 35°C. It was experimentally ascertained thatMnandMwof each sample determined by the present methods were in good agreement with the results of column fractionation, light scattering, and calculated values from molecular weight distribution curve within experimental errors. It is concluded that the present methods are useful for determiningMnandMw, since the reliabilities ofMnandMwvalues, which are fundamental quantities of polymer characterization, can be raised by comparing the experimental data observed by conventional methods such as osmotic pressure, light scattering, and the Archibald method with those observed by the p