Browsing by Author "Zografos, Aristotelis"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Supporting data for "Physical Aging of Polylactide Based Graft Block Polymers"(2019-11-08) Haugan, Ingrid; Lee, Bongjoon; Maher, Michael; Zografos, Aristotelis; Schibur, Haley; Jones, Seamus; Hillmyer, Marc; Bates, Frank; bates001@umn.edu; Bates, Frank; University of Minnesota Bates and Hillmyer research labsThese files contain primary data along with associated output from instrumentation supporting all results reported in Haugan et al. Physical Aging of Polylactide Based Graft Block Polymers. In Haugan et al. we found: Graft block polymers (BCPs) with poly(4-methylcaprolactone)-block-poly(lactide) (P4MCL-PLA) side chains containing 80 to 100% PLA content were synthesized with the aim of producing tough and sustainable plastics. These graft BCPs experience physical aging and become brittle over time. For short aging times, ta, the samples are ductile and shear yielding is the primary deformation mechanism. A double yield phenomenon emerges at intermediate ta where the materials deform by crazing followed by shear yielding. At long ta the samples become brittle and fail after crazing. PLA content strongly governs the time to brittle failure, where a 100% PLA graft polymer embrittles in 1 day, an 86% PLA graft BCP embrittles in 35 days, and at 80% PLA the material remains ductile after 210 days. Molecular architecture is also a factor in increasing the persistence of ductility with time; a linear triblock ages three times faster than a graft BCP with the same PLA content. SAXS and TEM analysis reveal the role of the rubbery P4MCL domains in initiating crazing by cavitation. Pre-straining the graft BCPs also significantly toughens these glassy materials. Physical aging induced embrittlement is eliminated in all the pre-strained polymers, which remain ductile after aging for 60 days. The pre-strained graft BCPs also demonstrate shape memory properties. When heated above Tg the stretched polymer within seconds returns to its original shape and recovers the original mechanical properties of the unstrained material. These results demonstrate that graft BCPs can be used to make tough, durable, and sustainable plastics and highlight the importance of understanding the mechanical performance of sustainable plastics over extended periods of time following processing.Item Supporting data for Impact of macromonomer molar mass and feed composition on branch distributions in model graft copolymerizations(2021-12-07) Zografos, Aristotelis; Lynd, Nathaniel A; Bates, Frank S; Hillmyer, Marc A; hillmyer@umn.edu; Hillmyer, Marc A; University of Minnesota, Department of ChemistryThese files contain primary data along with associated output from instrumentation supporting all results reported in the referenced manuscript. Graft polymers are useful in a versatile range of material applications. Understanding how changes to the grafted architecture, such as the grafting density (z), the side-chain degree of polymerization (Nsc), and the backbone degree of polymerization (Nbb), affect polymer properties is critical for accurately tuning material performance. For graft-through copolymerizations, changes to Nsc and z are controlled by the macromonomer degree of polymerization (NMM) and initial fraction of the macromonomer in the feed (fMM0), respectively. We show that changes to these parameters can influence the copolymerization reactivity ratios and, in turn, impact the side-chain distribution along a graft polymer backbone. Poly((±)-lactide) macromonomers with NMM values as low as ca. 1 and as high as 72 were copolymerized with a small-molecule dimethyl ester norbornene comonomer over a range of fMM0 values (0.1 ≤ fMM0 ≤ 0.8) using ring opening metathesis polymerization (ROMP). Monomer conversion was determined using 1H nuclear magnetic resonance spectroscopy, and the data were fit using terminal and non-terminal copolymerization models. The results from this work provide essential information for manipulating Nsc and z, while maintaining synthetic control over the side-chain distribution for graft-through copolymerizations.Item 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 ChemistryThese 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.Item Supporting data for Star-to-bottlebrush transition in extensional and shear deformation of unentangled polymer melts(2023-03-15) Zografos, Aristotelis; All, Helena A; Chang, Alice B; Hillmyer, Marc A; Bates, Frank S; bates001@umn.edu; Bates, Frank S; University of Minnesota Department Chemical Engineering and Material ScienceThese files contain primary data along with associated output from instrumentation supporting all results reported in Zografos et al. "Star-to-bottlebrush transition in extensional and shear deformation of unentangled polymer melts." A series of model poly((±)-lactide) (PLA) graft copolymers were synthesized using ring-opening metathesis polymerization and used to probe the star-to-bottlebrush transition in shear and extensional flows. Ten samples with backbone degrees of polymerization 10 < Nbb < 430, each containing one PLA side chain of length Nsc = 72 per two backbone repeat units, were investigated using small-amplitude oscillatory shear (SAOS) and extensional rheometry measurements. The star-like to bottlebrush transition was identified at Nbb = 50-70 using SAOS. In extension, melt strain hardening is absent in the star-like melts (Nbb < 50) but is prominent in the bottlebrush limit (Nbb > 70). The onset of melt strain hardening occurs at a timescale equivalent to the Rouse time of the backbone. A molecular interpretation of these results builds upon recent speculation related to strain-induced increases in interchain friction in bottlebrush polymers. These findings will be useful in designing bottlebrush melts to strain harden, which is critical in various types of processing methods involving extensional flows, including foaming, 3D printing, and film-blowing.Item Synthesis and Rheological Properties of Branched Polylactide(2023-08) Zografos, AristotelisPlastics 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.