Studies on the Application of Filter‐Based IR Detector for Polyolefin Characterization with HT‐SEC

Abstract

Even though polyolefins are simple polymers from a chemical structure point of view, their full characterization in practice is still an intriguing task. Basic macromolecular characteristics of polyethylene or polypropylene like molar mass moments and their distributions (MMD) but also chain conformation and thus information on long-chain branching, can be addressed with high-temperature sizeexclusion chromatography (HT-SEC). Hyphenation of infrared detection to sizeexclusion chromatography expands possibilities of SEC even more and allows to reveal comonomer incorporation across molecular weight and thus generate a fingerprint of a given catalytic system used in polyolefin synthesis. Multiband filterbased infrared detector gives an easy and fast access to so-called short chain branching distribution (SCB) vs MMD by coupling to HT-SEC. In this work, we summarize recent findings on application of a filter-based IR detector (IR5-MCT) towards characterization of polyolefins synthesized with different catalytic systems and varying comonomer types. It is found that for copolymers of polyethylene with 1-butene, 1-hexene or 1-octene (non-C3), one linear calibration line can be used in the range up to 70 CH 3 /1000TC, thus covering the range necessary for common applications like for instance HDPE or LLDPE. For ethylene-propylene copolymers (C3), over the broad range up to 333 CH 3 /1000TC, the calibration line is best fitted to a second order polynomial. C3 copolymers show a different behavior compared to non-C3 copolymers, irrespective the amount of comonomer incorporated in the polymer. We show that mixtures of PP and PE homopolymers result in equivalent response as the copolymers of the same average composition and thus can also be used to set up calibration lines. Based on this evaluation practical aspects of IR5-MCT calibration are discussed.

Precision, Tunable Deuterated Polyethylene via Polyhomologation

“…Given the distinct vibrational spectra for each dPE sample, we decided next to perform SEC-IR to determine the change in detector ratios as a function of deuteration. Typically, this technique has been used to determine short-chain branching (SCB) content in linear low-density polyethylene (LLDPE) by determining the ratio of the absorbances at the methyl asymmetric C–H stretching frequency (centered at approximately 2950 cm –1 ) and the entire alkyl C–H stretching region (2800–3000 cm –1 ) and comparing against a calibration curve . With regard to our series of dPEs, no methyl groups are expected, however each displays distinct IR spectra, with the intensity of each peak in the C–H stretching region (the asymmetric C–H stretch at 2920 cm –1 and the symmetric C–H stretch at 2850 cm –1 ) decreasing as deuterium content increases (Figure a).…”

“…Typically, this technique has been used to determine short-chain branching (SCB) content in linear low-density polyethylene (LLDPE) by determining the ratio of the absorbances at the methyl asymmetric C−H stretching frequency (centered at approximately 2950 cm −1 ) and the entire alkyl C−H stretching region (2800−3000 cm −1 ) and comparing against a calibration curve. 53 With regard to our series of dPEs, no methyl groups are expected, however each displays distinct IR spectra, with the intensity of each peak in the C−H stretching region (the asymmetric C−H stretch at 2920 cm −1 and the symmetric C−H stretch at 2850 cm −1 ) decreasing as deuterium content increases (Figure 3a). This leads to distinct differences in voltage response of the two IR concentration detectors for samples I−IV (Figures S7 and 3b) measured across the entire chromatogram.…”

Analysis of Propylene‐1‐Butene Copolymer Composition by GPC with Online Detectors

“…A more in depth study, including collection of high quality spectra by FTIR method, would be required to clarify this point, although for the case of ethylenepropylene copolymers it was found that there was no difference in the response of the IR detector to copolymers and homopolymer blends. [36] It must be noted that the accuracy of this GPC-IR method is related to the choice of reference materials used for calibration and how well they represent the unknown samples, given it is a relative method, while the LOD values given in Table 2 are only an indication of the precision.…”

Detection challenges in quantitative polymer analysis by liquid chromatography

“…The flow cell IR detector is often applied to determine short chain branching polyolefin blends where the methylene and methyl band can readily be distinguished in the IR spectra [117–120]. An in‐depth research on the quantitative aspects was recently published by Frijns‐Bruls et al.…”