Liquid chromatography at critical conditions of polyethylene

Liquid chromatography at critical conditions (LCCC) of poly(propylene) (PP) holds unique potential to further augment the understanding of molecular heterogeneities present in PP. The critical conditions for isotactic poly(propylene) (iPP) and syndiotactic poly(propylene) (sPP) have been identified using porous graphitic carbon as stationary phase and combinations of adsorption and desorption promoting solvents. It is found that 1,2,4-trichlorobenzene is a stronger desorption promoting eluent compared to 1,2-dichlorobenzene, while 2-octanol shows a weaker adsorption promoting effect compared to 2-ethyl-1-hexanol for all stereo-isomeric forms of PP. The fraction of desorption promoting solvent needs to reach critical conditions decreased in a linear manner with the temperature. High temperature 2D liquid chromatography with infrared detection provides quantitative information about the fractions of the constituents (iPP and ethylene-propylene copolymer) of a model high impact PP sample at LCCC of iPP.