Browsing by Author "Liffland, Stephanie"

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    Impact of Architecture on High-Performance Sustainable Aliphatic Polyester Thermoplastic Elastomers
    (2022-11) Liffland, Stephanie
    Thermoplastic elastomers (TPEs) are a class of reprocessable materials that behave like chemically crosslinked elastomers at their usage temperatures but can be processed like thermoplastic materials. This reprocessability is a result of the physical rather than chemical crosslinks present in the materials. Commercial TPEs are typically linear ABA triblock polymers with hard polystyrene endblocks and a soft polydiene midblock and have varied applications from adhesives to personal care products depending on composition . Unfortunately, these petrochemical-derived materials last long beyond their functional lifetimes and contribute to the growing problem of plastic waste. Aliphatic polyester-based TPEs (APTPEs) present an alternative to these non-renewable materials that can be sustainably derived from renewable biomass with enhanced degradation capabilities through recycling or composting. The best performing APTPEs consist of poly(L-lactide) and poly(γ-methyl-ε-caprolactone) and have shown to be competitive with commercial styrenic materials. The work presented in this thesis is focused on continued improvements to the mechanical properties of these APTPEs through alterations to the ABA triblock architecture. Chapter 1 provides an analysis of the methods in which we assess sustainable materials and background on thermoplastic elastomers. Chapter 2 investigates the influence of composite (i.e. glassy and semicrystalline) hard domains in ABCBA pentablock terpolymers. Chapters 3 details systematic investigations into the impact of symmetric multiarm star architectures on the mechanical performance of APTPEs. Chapter 4 further expands on the enhancements observed in the materials reported in Chapter 3 through the introduction of stereoblock PDLA-PLLA hard domains to star APTPEs. Chapter 5 details a study into the potential for high-performing star block APTPEs to act as sustainable medical devices.
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    Supporting Data for High Performance Star Block Aliphatic Polyester Thermoplastic Elastomers using PDLA-b-PLLA Stereoblock Hard Domains
    (2023-09-07) Liffland, Stephanie; Kumler, Margaret; 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 "High Performance Star Block Aliphatic Polyester Thermoplastic Elastomers using PDLA-b-PLLA Stereoblock Hard Domains" by Liffland et al. Star block (ABC)4 terpolymers consisting of a rubbery poly(γ-methyl-ε-caprolactone) (PγMCL) (C) core and hard poly(L-lactide) (PLLA) (B) and poly(D-lactide) (PDLA) (A) end-blocks with varying PDLA to PLLA block ratios were explored as high-performance, sustainable, aliphatic polyester thermoplastic elastomers (APTPEs). The stereocomplexation of the PDLA/PLLA blocks within the hard domains provided the APTPEs with enhanced thermal stability and an increased resistance to permanent deformation compared to non-stereocomplex analogs. Variations in the PDLA:PLLA block ratio yielded tunable mechanical properties likely due to differences in the extent and location of stereocomplex crystallite formation as a result of architectural constraints. This work highlights the improvements in mechanical performance due to stereocomplexation within the hard domains of these APTPEs and the tunable nature of the hard domains to significantly impact material properties, furthering the development of sustainable materials that are competitive with current industry standard materials.