Simplified Robust Triple Detection Methods for High Temperature GPC Analysis of Polyolefins

Abstract

Very powerful triple detector high-temperature gel permeation chromatography (HT-GPC) systems equipped with concentration, viscosity, and multiple angle light scattering detectors can be found in many polyolefin characterization laboratories. However, the complexity and sometimes lack of robustness of some detection methods often result in failure to achieve the required precision and long-term reliability to properly support the industrial needs. Two methods for data processing in triple detector HT-GPC of polyolefins are here described aiming at overcoming those difficulties, specifically those related to the application of multiple angle light scattering. In the first place, we propose here a data processing method using light scattering data collected at only one angle, with application of a dissymmetry correction based on an estimate of the molecular size from the hydrodynamic volume given by the universal calibration. This method (SALS DC : single-angle light scattering with dissymmetry correction) is simple and robust for molar mass distribution and averages. Long chain branching detection and quantification is another field plagued with lack of precision and inconsistency problems, due to the difficulty in collecting reliable radius of gyration (Rg) data using MALS, for calculation of the g-index. A novel approach to estimate the g-index, based on point-by-point calculation of the gpcBR index is here described and evaluated.

Fully Automated Instrument for Solution Viscosity in Polymeric Materials

“…[21] In the usual standard methods for determination of solution viscosity the shear rate was as high as 1000 s −1 , which means that Newtonian viscosity was actually measured. [13] In a capillary tubing the average shear rate 𝛾 ave could be calculated as: [28] 𝛾 ave = 8Q 3𝜋r 3 (11) Given that in this work the IVA capillary dimensions were fixed (radius r = 0.25 mm), the shear rate could only be varied by modifying the flow rate (Q). To determine intrinsic viscosity at near zero shear rates, polymer solutions must be measured at extremely low flow rates which would increase the analysis time beyond practical limits.…”

“…Another important application of dilute solution viscosity is the analysis of polymers with extremely high molar mass beyond the separation capacity of SEC columns. [11] Viscometers have also been successfully applied to the continuous online monitoring of polymerization reactions by Reed, [12] combined with other detectors (UV-vis, DRI, LS, etc.) and even separation techniques (SEC).…”

Recent Advances in Separation-Based Techniques for Synthetic Polymer Characterization

“…Knowledge of the scattering form factor would enable correction of the single angle scattering intensity. Recently, a method was proposed for estimating the scattering form factor without knowledge of solute radius of gyration . Additionally, branched and linear polyolefin materials were characterized by HT-GPC using a quadruple detector system, with the fourth detector being a DLS detector capable of direct determination of the R H .…”

Translating Simulated Chain Length and Molar Mass Distributions in Chain‐Growth Polymerization for Experimental Comparison and Mechanistic Insight

“…[48] One can also consider GPC triple detection and combine RI detection, viscometry, and dynamic light scattering to assess absolute MM values. [49,50] For more specialized information on advanced GPC detection, the reader is referred to the work of Berek. [47] However, some experimental pitfalls for SEC/GPC analysis exist such as i) less sensitivity for oligomeric species, complicating the correct representation of MMD fronting, [51] and ii) baseline instability, complicating the appropriate identification of specifically the MMD tail.…”

“…[ 48 ] One can also consider GPC triple detection and combine RI detection, viscometry, and dynamic light scattering to assess absolute MM values. [ 49,50 ] For more specialized information on advanced GPC detection, the reader is referred to the work of Berek. [ 47 ]…”