Visualization of Thermo‐Oxidative Degradation of Polyolefins in Solution Using HT‐SEC and HT‐AF4‐MALS

Abstract

The molar mass distributions of high‐molar‐mass PE and PP were characterized using HT‐AF4 and HT‐SEC in combination with IR and MALS detection. Calculated molar mass distributions, average molar masses and radii of gyration were compared. It was found that HT‐AF4 can detect the real extent of thermo‐oxidative degradation during dissolution. HT‐SEC is affected by shear and thermo‐oxidative degradation while in HT‐AF4 no shear stress exists. As a consequence, the molar mass averages obtained from HT‐SEC are pronouncedly lower as obtained from HT‐AF4. In addition, branched polyolefins cannot be correctly characterized by SEC‐MALS due to abnormal co‐elution effects. HT‐AF4 is therefore the method of choice for studying the thermo‐oxidative degradation of macromolecules with high molar masses. magnified image

Recent Advances in High-Temperature Fractionation of Polyolefins

“…Following the work of Mes et al, a number of detailed studies on the analysis of ultrahigh molar mass polyolefins were conducted by Otte et al [199][200][201][202][203]. It has been demonstrated that HT-AF4 enables one to separate ultrahigh molar mass samples up to a radius of gyration above 1,000 nm without the disturbing effects typical of SEC, namely the shear-degradation of high molar mass structures and the anomalous late co-elution effects.…”

“…Another interesting feature of HT-AF4 is that the thermo-oxidative degradation of polyolefins in solution can be visualized [203]. This approach can be used to evaluate effects that are caused by improper sample treatment including sample preparation for HT-SEC.…”

Importance of Multi‐Angle Light Scattering in Polyolefin Characterization

“…Concerning the determination of molar mass distribution one has to take into account a possibility of shearing degradation of high molar mass fractions . As high temperature asymmetric flow field flow fractionation is far from being a frequent technique, the high temperature SEC currently remains the major analytical separation tool in polyolefin research and manufacturing.…”

“…A general overview of MALS principles and theory can be found for example in references . In the polyolefin research and development the MALS detector has been applied to study long chain branching, the high molar mass tail in NIST SRM 1476 polyethylene (PE) standard, branching topology of polyethylenes prepared by palladium diimine catalysts, influence of long chain branching on viscoelastic flow properties and rheological behavior, thermorheological behavior, long chain branched poly(propylene)s prepared by electron beam irradiation, separation principle in SEC using polyethylene model polymers, thermo‐oxidative degradation, abnormal late co‐elution phenomenon, structural dependence of the linear steady‐state shear compliance, hyperbranched PE, multiarm star PE, ultra‐high molar mass PE, ethylene‐ graft ‐ethylene/propylene copolymers, processability at extrusion coating, end‐use performance of low density PE . Besides SEC, the MALS detection was also employed for high temperature asymmetric flow field flow fractionation …”

A review on the development of liquid chromatography systems for polyolefins

“…During the last several years, Pasch and Brüll in the German Institute of Polymers initiated research aiming to improve the analysis of polyolefins and potentially develop HPLC systems suitable for the analysis of polyolefins and functionalized polyolefins. As a result, Pasch et al elaborated new applications for known methods, such as CRYSTAF 52, 53, coupled high‐temperature SEC with FTIR (HT SEC‐FTIR) 53–59, coupled HT SEC with NMR (HT SEC‐NMR) 18, 60 and with DSC (HT SEC‐DSC) 57, and also used asymmetrical flow field‐flow fractionation to analyze polyolefins 61. In the meantime, novel HPLC systems applicable on the analysis of polyolefins have been developed, which will be described in the following text.…”