Browsing by Subject "star polymer"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    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 Science
    These 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.