Browsing by Subject "Polylactide"

Now showing 1 - 4 of 4
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    Fully-renewable and degradable thermoplastic elastomers.
    (2009-01) Wanamaker, Carolyn Leigh
    The most common polymers derived from renewable feedstocks, poly(3-hydroxybutyrate), polyglycolide, and polylactide (PLA), have high stiffness and tensile strength, but are inherently brittle, thus limiting the potential for these polymers to replace elastic and ductile polymers derived from fossil fuels. The work described in this thesis was directed toward expanding the properties of renewable resource polymers through the investigation of completely-biorenewable thermoplastic elastomers. Polymenthide (PM), a soft biorenewable polymer derived from (-)-menthol, is immiscible with PLA and was utilized as the middle block in a PLA-containing ABA triblock copolymer. Tensile measurements demonstrated impressive elongations and elastomeric properties typical of thermoplastic elastomers, however, the materials were relatively weak. The tensile properties of the polymers were found to be highly dependent on the molecular weight and crystallinity of the polylactide blocks. Substituting the amorphous PLA with semi-crystalline PLLA or PDLA significantly improved the strength of the material. Blends of the enantiomeric triblock copolymers further increased the strength through stereocomplexation of the enantiomeric polylactide segments. These results led to the investigation of stereocomplexed micelles as nucleating agents for PLLA. Quantifiable improvements in the nucleation efficiency of PLLA were observed when blending PLLA with PDLA-containing triblock copolymers. Finally, potential applications of these all-biorenewable triblock copolymers were investigated through hydrolytic degradation and adhesion studies. During hydrolytic degradation, the triblock copolymers were able to maintain a significant amount of their mechanical properties for many weeks.
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    Functionalized renewable polymers to toughen polylactide
    (2012-02) Gramlich, William Mike
    Sustainable polymers can overcome the limitations of petroleum sourced materials due to their renewable feedstocks, biodegradability, recyclability, and nontoxic nature. The renewably sourced polymer polylactide is commercially produced, but its use is limited by its brittle nature. Consequently, reactive melt blends of end-functionalized polylactide and renewably sourced conjugated soybean oil were investigated. End-functionalized polylactide and conjugated soybean oil reacted in the melt to produce compatibilizers that reduced the droplet diameter, yielding blended materials with improved elongation to break over the parent polylactide homopolymer. Additionally, polyisoprene, a potentially sustainable polymer, was investigated as a macroinitiator for tough polylactide graft polymers. Two methods were investigated to synthesize the polyisoprene macroinitiator: post-polymerization functionalization and isoprene copolymerization with a hydroxyl functionalized monomer. To this end, Conjugated polyisoprene was synthesized by a ruthenium hydride catalyst post-polymerization and subsequently functionalized with a hydroxyl containing maleimide through a facile Diels-Alder reaction. The post-polymerization functionalized conjugated polyisoprene produced well defined polylactide graft copolymers. Furthermore, the hydroxyl containing monomer 2-methylenebut-3-en-1-ol was copolymerized with isoprene in both reversible addition-fragmentation transfer controlled radical and emulsion polymerization schemes. In spite of Diels-Alder side reactions, the copolymerizations produced macroinitiators for polylactide graft polymer synthesis. Polylactide graft polymers made from polyisoprene macroinitiators gave microphase separated, potentially tough materials.
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    Structure-Property Relationships in Poly(lactide)-based Triblock and Multiblock Copolymers
    (2016-02) Panthani, Tessie
    Replacing petroleum-based plastics with alternatives that are degradable and synthesized from annually renewable feedstocks is a critical goal for the polymer industry. Achieving this goal requires the development of sustainable analogs to commodity plastics which have equivalent or superior properties (e.g. mechanical, thermal, optical etc.) compared to their petroleum-based counterparts. This work focuses on improving and modulating the properties of a specific sustainable polymer, poly(lactide) (PLA), by incorporating it into triblock and multiblock copolymer architectures. The multiblock copolymers in this work are synthesized directly from dihydroxy-terminated triblock copolymers by a simple step-growth approach: the triblock copolymer serves as a macromonomer and addition of stoichiometric quantities of either an acid chloride or diisocyanate results in a multiblock copolymer. This work shows that over wide range of compositions, PLA-based multiblock copolymers have superior mechanical properties compared to triblock copolymers with equivalent chemical compositions and morphologies. The connectivity of the blocks within the multiblock copolymers has other interesting consequences on properties. For example, when crystallizable poly(l-lactide)-based triblock and multiblock copolymers are investigated, it is found that the multiblock copolymers have much slower crystallization kinetics. Additionally, the total number of blocks connected together is found to eect the linear viscoelastic properties as well as the alignment of lamellar domains under uniaxial extension. Finally, the synthesis and characterization of pressure-sensitive adhesives based upon renewable PLA-containing triblock copolymers and a renewable tackifier is detailed. Together, the results give insight into the effect of chain architecture, composition, and morphology on the mechanical behavior, thermal properties, and rheological properties of PLA-based materials.
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    Supporting data for Synthesis, microstructure, and properties of high molar mass polyglycolide copolymers with isolated methyl defects
    (2021-06-15) Altay, Esra; Jang, Yoon-Jung; Kua, Xiang Qi; Hillmyer, Marc; hillmyer@umn.edu; Hillmyer, Marc; University of Minnesota, Hillmyer Lab, Department of Chemistry
    An efficient, fast and reliable method for the synthesis of high molar mass polyglycolide (PGA) in bulk using bismuth (III) subsalicylate through ring-opening transesterification polymerization is described.The difference between the crystallization (Tc ≈ 180 °C) / degradation (Td ≈ 245 °C) temperatures and the melting temperature (Tm ≈ 222 °C) significantly impacts the ability to melt process PGA homopolymer. To expand these windows, the effect of copolymer microstructure differences through incorporation of methyl groups in pairs using lactide or isolated using methyl glycolide (10% methyl) as comonomers on the thermal, mechanical and barrier properties were studied. Structures of copolymers were characterized by Nuclear Magnetic Resonance (1H and 13C NMR) spectroscopies. Films of copolymers were obtained, and the microstructural and physical properties were analyzed. PGA homopolymers exhibited approximately 30 °C difference between Tm and Tc, which increased to 50 °C by incorporating up to 10% methyl groups in the chain while maintaining overall thermal stability. Oxygen and water vapor permeation values of solvent cast non-oriented films of PGA homopolymers were found to be 4.6 (cc.mil.m-2.d-1.atm-1) and 2.6 (g.mil.m-2.d-1.atm-1), respectively. Different methyl distributions in the copolymer sequence, provided through either lactide or methyl glycolide impacted the resulting barrier properties. At 10% methyl insertion using lactide as a comonomer significantly increased both O2 (32 cc.mil.m-2.d-1.atm-1) and water vapor (12 g.mil.m-2.d-1.atm-1) permeation. However, when methyl glycolide was utilized for methyl insertion at 10% Me content, excellent barrier properties for both O2 (2.9 cc.mil.m-2.d-1.atm-1) and water vapor (1.0 g.mil.m-2.d-1.atm-1) were achieved.