Summary: A compact automated instrument has been developed for measuring the bivariate distribution by TREF fractionation and subsequent GPC analysis of the fractions in a single run. The configuration of this instrument and its operation principles are covered here. High resolution TREF fractionation of HDPE and fast methods with overlapped GPC injections are also discussed. Future developments, such the addition of comonomer or molar mass sensitive detectors, as well as operation in GPC -TREF mode for broad MWD resins are outlined.

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.

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Summary: An infrared detector based on a set of narrow band optical filters was coupled to a high temperature Gel Permeation Chromatograph (GPC) producing continuous chromatograms of absorbance after the molar mass fractionation. A multiple linear regression (MLR) model was established to relate the measured absorbance to the average octene weight percent in industrial ethylene-octene copolymer samples. This method is compared to univariate and multivariate band ratio models. The application of these models to produce molar mass compositional distributions is also outlined.