Browsing by Author "Haugan, Ingrid"
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Item Graft Polymer Physics(2010-05) Haugan, IngridGraft polymers have polymeric side chains grafted onto a common backbone and exhibit extended conformations due to steric repulsion from densely grafted side chains. The ability to modulate conformation, and thus material performance, has made graft polymers a rich area of research in the last decade. This thesis expands the fundamental understanding of the physical properties of graft polymers in order to aid in the design of novel materials and focuses in three areas: rheology, thermodynamics, and mechanical properties. First, the effect of grafting density on the linear viscoelasticity of graft polymers is investigated. We demonstrate that graft polymers experience the same relaxational modes as linear polymers and their viscoelastic behavior can be described by the same Rouse and reptation theories. The experimental data is compared to scaling models to determine the conformation of the graft polymers, and a new model is proposed to better capture the behavior of experimentally relevant graft polymers. Next, the thermodynamics of densely grafted bottlebrush block polymers is explored. Bottlebrush block polymers were prepared with homopolymer side chains added in blocks along the backbone, varying side chain and backbone length. Their order-disorder transition temperatures were measured by temperature controlled small-angle X-ray scattering. The bottlebrush block polymers display a higher segregation strength compared to linear diblock polymers at the order-disorder transition, indicative of the shielding of the segments near the backbone. The segregation strength at the order-disorder transition decreased with increasing side chain and backbone length. Finally, the mechanical properties of graft polymers with diblock side chains are studied in an attempt to produce tough and sustainable polylactide plastics. The addition of a rubber domain initially toughens the polylactide but the polymers still undergo physical aging and become brittle over time; the time to brittle failure is found to be strongly dependent on the rubber content of the graft block polymers. Pre-straining of the polymers is used to produce stronger and tougher plastics that do not embrittle upon aging.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.