Determination of Crystallinity by Gas Chromatography. Effect of Curvilinearity of Retention Diagrams

Abstract

Gas phase nonideality and changes in heat of vaporization of solute molecules with temperature cause a departure from linearity of gas chromatographic retention diagrams. The determination of the crystalline content of polymer stationary phases, involving a linear extrapolation of measured retention data, can thus lead to erroneous estimates of crystallinity. Studies of several polyolefin stationary phases reveal that the phenomenon is dependent on both experimental conditions and temperature. Computed crystallinities were found to vary by as much as 50%. It is shown that these discrepancies can be alleviated by proceeding to curvilinear extrapolations of retention data based on readily available solute vapor pressure data and second virial coefficients. © 1977, American Chemical Society. All rights reserved.