Experimental Validation of the Molecular Weight Distribution (MWD) and Chemical Composition Distribution (CCD) Deconvolution Method for Polyolefins Made with Ziegler-Natta Catalysts

  • Author / Creator
    Raj, Raunil
  • Polyolefins are important commodity polymers. They account for more than 50 wt% of the total polymers produced in the world. Ziegler-Natta and Phillips catalysts, discovered in 1950, revolutionized the material science arena. Even 70 years after their invention, they continue to be responsible for most of the polyolefin production.
    Ethylene/1-olefin copolymers made with Ziegler-Natta or Phillips catalysts have broad molecular weight distributions (MWD), a deviation from Flory most probable distribution. Additionally, their average 1-olefin content depends on polymer molecular weight, a deviation from Stockmayer distribution. This behavior is attributed to the presence of more than one type of active site in these catalysts. Numerical deconvolution methods have been used to estimate the minimum number of active site types needed to explain the microstructure of polyolefins made with these catalysts. These methods have been used to successfully describe polyolefins made in laboratory and industrial reactors, permit the development of useful simulation programs, but have never been tested from a fundamental point of view.
    In this thesis, I developed a method to validate these deconvolution techniques experimentally. I synthesized ethylene/1-hexene copolymers with a commercial Zeigler-Natta catalyst, and measured and deconvoluted their molecular weight distribution (MWD) and chemical composition distribution (CCD) to determine the minimum number of Flory/Stockmayer polymer populations needed to represent these distributions. Then, I synthesized polymers with these single-site distributions with a metallocene catalyst and blended them in the proportions determined by the deconvolution procedure to find out whether these blends had the same microstructural properties of the polymers made with the multi-site Zeigler-Natta catalyst. In the
    process, I established different deconvolution approaches to enhance the predictive power of this proposed method.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.