Browsing by Subject "polymer architecture"

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    Supporting data for Preparation and characterization of H-shaped polylactide
    (2024-05-16) Zografos, Aristotelis; Maines, Erin, M; Hassler, Joseph, F; Bates, Frank, S; Hillmyer, Marc, A; hillmyer@umn.edu; Hillmyer, Marc, A; University of Minnesota Department of Chemistry
    These files contain primary data along with associated output from instrumentation supporting all results reported in Zografos et al. Preparation and Characterization of H-Shaped Polylactide. In Zografos et al. we developed an efficient strategy for synthesizing H-polymers. An H-polymer has an architecture that consists of four branches symmetrically attached to the ends of a polymer backbone, similar in shape to the letter ‘H’. Here, a renewable H-polymer efficiently synthesized using only ring-opening transesterification is demonstrated for the first time. The strategy relies on a tetrafunctional poly(±-lactide) macroinitiator, from which four poly(±-lactide) branches are grown simultaneously. Proton nuclear magnetic resonance (1H-NMR) spectroscopy, size exclusion chromatography (SEC), and matrix assisted laser desorption/ionization (MALDI) spectrometry were used to verify the macroinitiator purity. Branch growth was probed using 1H-NMR spectroscopy and SEC to reveal unique transesterification phenomena that can be controlled to yield architecturally pure or more complex materials. H-shaped PLA was prepared at the grams scale with a weight average molar mass Mw > 100 kg/mol and narrow dispersity Ð < 1.15. Purification involved routine precipitations steps, which yielded products that were architecturally relatively pure (~93%). Small-amplitude oscillatory shear and extensional rheology measurements were used to demonstrate the unique viscoelastic behavior associated with the H-shaped architecture.
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    Synthesis and Rheological Properties of Branched Polylactide
    (2023-08) Zografos, Aristotelis
    Plastics are essential to society but the current trends of their production, use, and end-of-use are not sustainable. This realization has created a push towards more circular approaches to plastics management and central to this is the transition away from petroleum-based feedstocks towards those that are biobased and inherently renewable. This shift not only relies on the development of new biobased polymers but also the expanded use of those currently available. Polylactide has found its place as a key material in the biobased plastics market and is projected to remain so for the foreseeable future. However, its use is hampered by its poor melt processability in extensional flows. The work in this dissertation has sought to better understand how the polymer architecture can improve this limitation. The research presented here describes the means of implementing PLA into an architecture with precision branching and the study of how controlled changes to the branching influences the melt flow behavior. The introduction to this dissertation overviews general concepts of extensional rheology and branched polymer dynamics, which are important to the research. Chapter 2 discusses how to create graft polymers of PLA and focuses on the effects of monomer size and feed composition on the copolymerization kinetics for a graft-through synthesis. Chapter 3 uses this chemistry to synthesize a library of model graft copolymers to study how changes to the architecture influence viscoelasticity in extensional and shear deformations. In Chapter 4, a new method for synthesizing H-shaped PLA homopolymers is presented and the associated rheological properties are compared to a linear analogue. Taken together, these works further the ability to synthesize polymers with controlled branching and broadens the understanding of how specific changes to the branching can influence the rheological melt behavior. These ideas can be leveraged to target materials with viscoelastic properties amenable to industrial processing flows so that they can be used for a broader variety of applications.