Multidimensional high‐temperature liquid chromatography: A new technique to characterize the chemical heterogeneity of Ziegler‐Natta‐based bimodal HDPE

Abstract

High temperature two-dimensional liquid chromatography (HT 2D-LC) was recently introduced as a new technique to analyze the heterogeneities with regard to composition and molar mass present in model blends of polyolefins and various olefin copolymers. The method uses graphite as stationary phase and solvent gradients of 1-decanol 1,2,4-trichlorobenzene as mobile phase for the compositional separation. With the aim to maximize the chromatographic resolution, the influence of the separation's temperature in the first dimension was evaluated: approaching the -temperature of polyethylene (PE) in 1-decanol selectively enhances the retention of higher molar mass PE standards while that of the lower molar mass ones is hardly affected. A bimodal ethylene/1-butene copolymer and its temperature rising elution fraction (TREF) fractions were separated by HT 2D-LC. For the first time, both axes of the contour plot were calibrated with regard to chemical composition and molar mass, respectively. Prefractionation of the bulk sample by TREF enhances the detectability of separated components of the 2D separation. The influence of the separation temperature, that is, working around the theta-temperature of PE in 1-decanol, can be used to enhance the chromatographic resolution of the 2D chromatography

Separation of bimodal high density polyethylene using multidimensional high temperature liquid chromatography

“…the elution volume of the analyte should decrease [87,88]. This was observed in HPLC of BiHDPE in the temperature range 140−180 • C by Ginzburg et al [81]. As a consequence of the presence of significant portions of high molar mass material in the LLDPE investigated here (Fig.…”

“…4). 1-decanol was chosen as adsorption promoting liquid as the retention of HDPE is larger in comparison with other solvents like 2-octanol and 2-ethyl-1-hexanol and furthermore dissolution was good in 1-decanol [59][60][61][62][63][64][65][66][67][68][69][70][71][72][73]81] and TCB, which is the solvent commonly used in SEC of polyolefins, was applied as desorption promoting liquid. Fig.…”

“…A short SEC column (150 × 7.5 mm, L. x I.D.) was used in our previous [81] and current HT 2D-LC measurements (Figs. 11-13), which aims Table 2).…”

“…An evaporative light scattering detector (ELSD), model PL-ELS 1000 (Polymer Laboratories), was used: The nebulizer temperature and the evaporation temperature were set to 160 and 260 • C, respectively, and the nitrogen flow rate was 1.5 L/min. The gradient reaches the detector with a delay of 3.7 min, which was determined according to method of Ginzburg et al [81]. A linear gradient (G) 1-decanol→TCB, generated by a binary gradient pump (model 1200, Agilent, Waldbronn, Germany), was applied.…”

“…These separations were hyphenated with the separation with regard to molar mass, and experimental protocols for 2D-LC (HPLC × SEC) [75][76][77] have been applied for HT 2D-LC of a range of olefin copolymers [64][65][66][67][68][69][70][71][78][79][80][81][82]. Ginzburg et al [81] were the first to investigate BiHDPE using HT 2D-LC and examined the effect of temperature on the separation. In this study, we want to show how the experimental parameters of the individual dimensions can be used to maximize the chromatographic information.…”