On the molecular weight determination by vapour pressure osmometry, 1. Consideration of the calibration function

A detailed study on the calibration of vapour pressure osmometry (VPO) using thirteen different samples (eight of them polystyrenes) in a range of molecular weights up to 50 000 as solutes and chloroform, dichloromethane, ethyl methyl ketone, cyclohexane, and acetone as solvents is carried out. The results show that contrary to the commonly used calibration equation M = K · (Δ V / c ) , the relationship between the measuring result (Δ V / C ) c =0 and molecular weight M obeys a function of the type M = K · (Δ V / c ) in which the exponent a differs from 1. For each of the above mentioned solvents the values of K and a are determined. The limits of applicability of VPO with respect to polymers are discussed in view of these terms and recent theoretical considerations.