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

Abstract

In this paper, a robust short-chain branching (SCB) determination technique recently developed using IR5-detected GPC (GPC-IR5) for polyethylene resins is reported, wherein the IR5 detector is an infrared detector equipped with five filters set at different frequency ranges and a mercury-cadmium-telluride detector with thermoelectric cooling capability. Both intensity ratios of methyl/methylene and methyl/all C─H groups have very good linear relationship with the SCB content. Based on these relationships, an excel spreadsheet method is developed to deduce the SCB distribution across the molecular weight distribution using in-house developed algorithms. The uncertainty of SCB determination using the GPC-IR5 technique is found to be chromatographic signal-to-noise ratio dependent and can be explicitly expressed and calculated slice by slice. The SCB uncertainty is also found to be a function of experimental conditions and environment, which can affect not only the signals but also the noise levels at different IR bands. At a given polymer concentration, the higher the SCB content, the smaller the relative error bars. The SCB detection limit of this GPC-IR5 technique is found to be at ≈0.5-1.0 SCB per 1000 TC for all samples tested. Some practical aspects for application of this technique are also discussed in this paper.

High temperature‐size exclusion chromatography with triple detection to assess the molecular architecture of low‐density polyethylene: Insight into branching and processability correlations

“…Recently, SEC coupled with IR-5 detection also in practice to determine SCB distribution for polyolefins which gives information of SCB distribution across the MWD [30]. It was reported that SEC-IR-5 detection also suffers from certain limitations that detection limit of this technique was found to be ∼0.5-1.0 SCB/1000TC, this uncertainty is attributed by experimental conditions and environment, which can affect not only the signals but also the noise levels at different IR bands [15]. However, LDPE typically exhibits 10 to 30 SCBs per 1000 carbon atoms, and the LCB density is only 1-3 per 1000 carbon atoms as evident from earlier reported findings [10] hence detection limit is not the concern in the case of LDPE while using SEC-IR-5 as a detection tool.…”

“…Based on the prior art analysis, researchers have reported standalone techniques, for example, nuclear magnetic resonance (NMR) [13], Fourier-transform infrared (FT-IR) spectroscopy [14], GPC-IR-5 [15] methods to measure the SCB distributions. On the other hand, tradi-tional LCB determinations methods are also in practice, for example, rheology [16,17], NMR [18], high temperature-size exclusion chromatography (HT-SEC) with triple detectors (DRI/Visco/RALS/LALS) [19,20], SEC-multiangle light-scattering (SEC-MALS) [21,22], SEC-MALS/VISCO [23,24], SEC-IR-VISCO-MALS [25], or combination of 13 C NMR and SEC methods to quantify the LCB/SCB in LDPE resin [26].…”