High temperature thermal field‐flow fractionation of polyethylene and polystyrene

Abstract

In this paper the high‐temperature thermal field flow fractionation method is exploited for the analysis of polyethylene (PE). The experimental apparatus set‐up, obtained by simply modifying a commercial instrument, is presented. The numerical procedure for deriving retention calibration plot versus molecular weight is discussed with reference to the specific polymer‐solvent pair, PE‐o‐dichlorobenzene (ODCB), here employed. Different methods for computing the physicochemical data set of the solvent, necessary for calibration, are compared. The selectivity of the checked PE‐ODCB system proves comparable with respect to the values currently found in thermal field‐flow fractionation (ThFFF) analysis. Differences are found between PE and polystyrene (PS) analysis in the same solvent. The conditions for high temperature ThFFF operation in PE analysis and their advantages are discussed with respect to the standard SEC technique for PE, PS, and PE‐PS copolymer analysis. Molecular weight distributions obtained by ThFFF of two PE commercial samples agree with those obtained by SEC. © 1995 John Wiley & Sons, Inc.

The Role of Solubility in Thermal Field-Flow Fractionation: A Revisited Theoretical Approach for Tuning the Separation of Chain Walking Polymerized Polyethylene

“…Yet, the yielded blob diameter for THF may represent here only a lower limit of its actual size, because DT data from ThFFF are not fully resolved due to the poor retention. The blob diameter found for cwPE in ALK and DEC as well as the retraced values for HDPE from literature retention 38,39 and scaling data 85,86 (transformed to 25 °C for comparison) in ODBC and TCE are in close agreement to the segment lengths reported for short chain branched (SCB) PE. For SCB-PE a persistence length ranging from 0.9 nm for high numbers of SCB to 0.6 nm for non-branched PE chains is reported.…”

The Role of Solubility in Thermal Field Flow Frac-tionation – A Revisited Theoretical Approach for Tuning the Separation of Chain-Walking Polymerized Polyethylene

“…[7][8][9]37 ThFFF in high temperature mode has been already successfully applied for regular polyethylene separation. 38,39 However, an extension of the analysis scope towards polymer topology has not been tried yet. One aim in this study is to predict suitable separation conditions for a branching characterization of regular polyolefins by HT-ThFFF.…”

Determination of calibration function in thermal field flow fractionation under thermal field programming

“…The fact that the ThFFF separation system is made up of a flat, ribbon-like channel, free of any packing material allows one to separate polymers and microgels (e. g. see [6]), without any of the adverse effects encountered in SEC. ThFFF is also suitable for polyolefin analysis which usually requires high temperatures to achieve sample solubility [7]. In fact the temperature limit in ThFFF is only dictated by the thermal stability of the channel spacer.…”

“…where k is the basic FFF parameter (see below) which can be obtained from the retention time of a species of given M [7]. c 1 and c 2 are the calibration constants.…”