Characterization of Chemical Composition along the Molar Mass Distribution in Polyolefin Copolymers by GPC Using a Modern Filter‐Based IR Detector

Abstract

Summary Gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC), is the technique routinely used at high temperature to analyze the molar mass distribution in polyolefins. The distribution of comonomer along the molar mass distribution in a copolymer is a key microstructural feature that determines the macroscopic properties of the material, and thus, its range of possible applications and performance. The direct coupling of a modern filter‐based infrared (IR) detector to a high temperature GPC instrument, by means of a heated flow‐through cell, is here described. The analyses are carried out by recording the continuous IR absorbance chromatograms at selected bands, which show different sensitivities to the different monomer units. A slice‐by‐slice ratio of the IR bands is further calculated to determine the average chemical composition of each molar mass fraction, after GPC separation. The high sensitivity of this IR detection method allows the injection of low concentrations of sample and the use of standard GPC analysis conditions, so that chromatographic quality is not compromised even in cases where very high molar mass fractions are present. The analysis of comonomer variations along the molar mass distribution in polyolefin copolymers is discussed. Selected applications of the method to polyethylene and poly(propylene) copolymers are presented.

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

“…Prabhu et al / J. Chromatogr. A xxx (2015) xxx-xxx in SEC of ethylene/1-alkene copolymers [14,64,[98][99][100]. Only a few IR-transparent solvents (C-H absorbance) exist: TCB, ODCB, TCE and 1-chloronapthalene.…”

“…As a result, BiHDPE exhibits a comonomer distribution such that the comonomer content decreases toward the low and high molar mass. The crystalline regions are mainly formed by the low molar mass homopolymer PE as well as the ethylene sequences in the copolymer fractions as the comonomer is rejected each hydrodynamic volume may be determined, but not the corresponding CCD, as copolymers with different compositions will co-elute [11][12][13][14][15][16].…”

A Short‐Chain Branching Distribution Determination Technique for Polyethylene Using IR5‐Detected GPC

“…In more recent years, high temperature GPC coupled with fixed‐bands infrared detector equipped with thermoelectric cooling capability has been demonstrated to be a robust technique for SCB distributional determination for PO copolymers largely because of the ease of data processing, continuous operation, and no need for employing liquid nitrogen to cool the detector. [ 9–12 ] In this paper, we report a new polyethylene SCB distribution determination technique developed in our group using an IR5‐detected GPC (GPC‐IR5) system, wherein IR5 is a fixed‐band infrared spectrometer that is equipped with a thermoelectric‐cooled mercury‐cadmium‐telluride (MCT) detector and optical filters set at five frequency regions for C─H stretching bands (thus IR5). [ 13,14 ] We will first describe SCB calculation algorithms and the detector calibration method, which will be followed by error analysis and discussion of practical aspects in application of this technique.…”

Development of an Integrated On‐Line 2D Analytical TREF‐High Throughput SEC Technique for Polyolefins Characterization

“…As a result, polymers with the same molecular weight ( M W ) and molecular weight distribution (MWD) or even exactly the same MWD profile can have remarkably different mechanical properties. Although much effort has been made in characterizing polymer compositions at the chromatographic slice level using combined techniques, [ 6,10,12,21–27 ] the very issue is that all those techniques measure an average of chemical composition (or short‐chain branching, SCB) for each chromatographic slice while in reality there can be both inter and intra‐molecular SCB distributional heterogeneity present in polymers eluting at the same chromatographic slice. [ 14 ]…”