Determination of Short Chain Branching in LLDPE by Rheology

• Published in: Macromolecular chemistry and physics Vol. 223; no. 20
• Main Authors: Usanase, Gisèle, Fraisse, Frédéric, Taam, Manel, Boyron, Olivier
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-10-2022; Wiley-VCH Verlag
• Subjects: Chain branching; Chemical composition; Chemical Sciences; Copolymers; Crystallization; Fractionation; LLDPE; Low density polyethylenes; Material properties; NMR; Nuclear magnetic resonance; Polyolefins; Rheological properties; Rheology; short chain branching; Size exclusion chromatography
• ISSN: 1022-1352; 1521-3935
• DOI: 10.1002/macp.202200150

The relationship between the structure and the final properties of materials is an important issue in polymer science. In particular, the properties of polyolefins are impacted by their branching contents. A simple rheological method is presented to estimate the degree of short chain branching (SCB) in linear low‐density polyethylene (LLDPE). A range of ethylene‐1‐hexene copolymers is synthetized using a metallocene catalyst to obtain homogenous LLDPE models with various comonomer contents. The polymers are analyzed by size exclusion chromatography, 13C NMR, and crystallization elution fractionation to determine both their molar masses and their chemical composition distributions. Subsequently, they are measured by rheology to assess the impact of SCB. This work provides calibration curves for rheology and proves that it is possible to predict the SCB content in LLDPE from the melt viscosity analysis.
The properties of linear low‐density polyethylene (LLDPE) are influenced both by their molar masses and by the presence of long and short chain branching (LCB and SCB). While the measurement of LCB by rheology is well known, this work highlights that it is also possible to efficiently determine the SCB content in LLDPEs by exploiting rheological data.