MOLECULAR WEIGHT DETERMINATION OF POLYSTYRENE STANDARDS BY VAPOR PRESSURE OSMOMETRY

Number average molecular weights [formula-omitted] of polystyrene standards in the range 600 to 400,000 have been measured in benzene, carbon tetrachloride, and cyclohexane with a standard deviation of 1 to 12% by using an extended range vapor pressure osmometer. The values found for [formula-omitted] above 8,000 are lower than the nominal values obtained by membrane osmometry but are identical for different solvents. Determinations on polymer mixtures are consistent with the values calculated from these results. A plot of 1/Mapp vs. concentration follows a three term virial expansion. Neither the Flory-Huggins nor the Flory-Krigbaum equations give an adequate fit over the concentration range studied. To reduce the standard deviation of the extrapolated [formula-omitted] the following procedures have been applied to allow a straight line extrapolation: measurement in a θ-solvent where the second virial coefficient equals 0, third term correction, and application of Maron 's equation in a concentration ange below 3 grams/100 cm3. © 1969, American Chemical Society. All rights reserved.