Molecular weight characterization of polybutadiene rubber with high molecular weight and broad molecular weight distribution

Abstract

AbstractFollowing the molecular weight characterization of two polybutadiene samples, it was found that Mw from gel permeation chromatography with universal calibration and light scattering were in agreement, but Mn by gel permeation chromatography was less than Mn from membrane osmometry. A more detailed analysis revealed that the high molecular weight and broad molecular weight distribution of the two samples forced two corrections to the membrane osmometry results for (a) diffusional layer effects caused by high solution viscosities, and (b) solute permeability of the membrane. In the latter effect, the high viscosities of the solutions prevented actual diffusion through the membrane, but “reflection” of these species as defined by the Staverman coefficient prevented an accurate Mn determination. After making these corrections, it was found that Mn from membrane osmometry using a very tight membrane was in very good agreement with Mn from gel permeation chromatography. A method is demonstrated for obtaining Mn from a combination of membrane osmometry and gel permeation chromatography, where membrane osmometry data from membranes of different porosities (after corrections for diffusional layers and membrane reflection) are used to verify the accuracy of the gel permeation chromatography data as representing the true molecular weight distribution, allowing the gel permeation chromatography data to be used to calculate Mn.