Browsing by Subject "Metathesis"

Now showing 1 - 5 of 5
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    Accessing Model, Functional Polyolefins and Polyolefin Copolymers with Ring-Opening Metathesis Polymerization
    (2022-11) Dingwell, Claire
    Polyolefins are the most widely used commercial polymer available due to their low cost and excellent properties. Functionalized polyolefins with polar functional groups are desirable targets for more complex materials benefiting from the excellent properties of polyolefins, but these materials are challenging to synthesize using traditional polymerization methods. Ring-opening metathesis polymerization (ROMP) is a useful tool for achieving this goal as the catalysts are often tolerant to a wide range of functional groups, and the polymerizations are typically well-controlled making polymers with moderate dispersities. Chapter 2 describes the synthesis of epoxy-telechelic polyalkenamers and polyolefins made by ROMP of a cyclooctene-based monomer with difunctional chain-transfer agents. These polymers can then be rapidly photocured into model elastomers with few dangling-end defects and tunable properties based on the degree of saturation and the prepolymer molar mass. Appendix A shows the synthesis of similar elastomers made from polymers containing epoxide groups along the backbone of the polymer chain to explore the contributions of dangling-end defects to the mechanical properties of the final material. Chapters 3 and 4 describe the synthesis of a gas barrier polymer, an ethylene vinyl alcohol (EVOH) copolymer, made by ROMP of 3-functional cyclooctene. Chapter 3 explores the effect of regioregularity, given by ROMP of cyclooctenes with substituents in the 3 position, on the barrier properties of EVOH with the goal of decreasing the oxygen permeability of EVOH with high ethylene content while maintaining low water permeability. Chapter 4 discusses the additional effects of stereoregularity on the properties of a similar EVOH polymer. Appendix B describes the attempted synthesis of a disubstituted ROMP monomer for the synthesis of EVOH copolymers containing a higher vinyl alcohol copolymer content compared to the polymers made in Chapters 3 and 4. Finally, Appendix C presents the compilation and discussion of data from learning experience reports, an anonymous accident reporting system from the joint safety team.
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    The acquisition of consonant feature sequences: Harmony, metathesis and deletion patterns in phonological development.
    (2010-12) Gerlach, Sharon Ruth
    This dissertation examines three processes affecting consonants in child speech: harmony (long-distance assimilation) involving major place features as in coat [kok]; long-distance metathesis as in cup [pak]; and initial consonant deletion as in fish [is]. These processes are unattested in adult phonology, leading to proposals for child-specific constraints. Initial consonant deletion in particular is a little-understood phenomenon thought to be idiosyncratic. However, my survey of initial consonant deletion as reported in eight languages reveals systematic deletion patterns affecting continuants and sequences of different consonants. I argue that all of these child-specific processes are tied to the acquisition of consonant sequences. In order to understand the role of these processes in phonological development, I examine consonant acquisition data from a diary study of Grace, an English-acquiring child. I adopt the Bernhardt and Stemberger (1998) variant of Optimality Theory for the analysis since their view of default underspecification, sequences of features, and feature-based approach to sonority permit a unified analysis of harmony, metathesis and initial consonant deletion that explains Grace's trajectory of acquisition as well as the frequency of certain patterns across children. I show that independently motivated constraints governing feature sequences, onset sonority preferences, initial velars, and the tendency to anticipate features within a prosodic domain explain all of these processes, as well as Grace's onset cluster reduction patterns (e.g. snake [seɪk]) and gradual acquisition of different cluster types. Children must learn to produce consonant feature sequences within a word before producing sequences within an onset. Child-specific processes are eliminated as children acquire the speech planning skills necessary to express the contrasts of a mature language, though the constraints remain active in adult phonology. The longitudinal data provide evidence for both constraint demotion and promotion in learning, as well as distinct roles for two types of faithfulness constraints. One mandates the preservation of non-default features that are specified in the underlying representation, while the other evaluates identity of a correspondent segment to any non-default feature associated with a segment. This distinction permits the derivation of initial consonant deletion as a response to positional constraints on features or feature sequences.
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    Fabricating robust nanoporous materials and polymer electrolyte membranes from reactive block copolymers by metathesis reactions.
    (2009-06) Chen, Liang
    Polymer membranes have been studied for several decades, and conventional utility of these membranes has been realized over a wide range of applications such as water purification, gas separation, and fuel cells. Separation performance of polymer membranes for these applications can be evaluated from different aspects including selectivity, material cost, and thermal and mechanical stabilities. This research focused on the design of crosslinked polymer membranes from reactive block copolymers, which could possess some attractive features such as controlled functionality and morphology. Novel block copolymers containing a chemically crosslinkable block and a chemically modifiable block were of particular interest. Metathesis reactions were employed to crosslink these copolymers with additional tough polymers such as polycyclooctene (PCOE) and polydicyclopentadiene (polyDCPD), to realize enhanced toughness in the resulting materials. First, a norbornene-functionalized polystyrene-polylactide (PNS-PLA) block copolymer was synthesized. A self-assembled blend containing this copolymer and DCPD was cured by metathesis reactions, and nanoporous monoliths with a cylindrical morphology were successfully produced after removing the PLA component. These monoliths exhibited pronounced mechanical and thermal stabilities superior to nanoporous polystyrene (PS). Second, polymerization induced phase separation (PIPS) during the ring-opening metathesis polymerization (ROMP) of DCPD in the presence of the PNS-PLA copolymer rendered continuous PLA nanodomains in a crosslinked PNS/polyDCPD matrix. Upon etching the PLA component, the resultant nanoporous membranes exhibited well-defined percolated nanopores and good thermal and mechanical stabilities. Preliminary diffusion measurements demonstrated potential utility of such membranes in ultrafiltration. Third, crosslinked polymer electrolyte membranes (PEMs) were fabricated from a PNS-poly(n-propyl-p-styrenesulfonate) (PSSP) block polymer and COE/DCPD via the PIPS scheme followed by deprotection of the PSSP block. These PEMs possessed a bicontinuous morphology and mechanical and thermal robustness. Select PEMs exhibited high proton conductivity similar to Nafion at high humidity and reduced methanol crossover. Tunable domain size and mechanical strength of the resulting PEMs are advantageous attributes of this preparation protocol. Additionally, the use of such PEMs for NH3 separation from gas mixtures was demonstrated. The appendix chapter represented our efforts to produce amine-functionalized polymer membranes from PNS-poly(dimethylaminoethylmethacrylate) (PNS-PDMAEMA) and COE by metathesis reactions, potentially useful for CO2 separation from gas mixtures.
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    Filler Reinforced Elastomers Based on Functional Polyolefin Prepolymers
    (2015-05) Ren, Ning
    Carboxy-telechelic polyethylene prepolymers were synthesized by ring-opening metathesis polymerization of 3-ethyl-1-cyclooctene in the presence of maleic acid followed by hydrogenation. Crosslinking of the prepolymer with a tri-functional crosslinker and fumed silica or carbon black filler yielded polyethylene elastomers with enhanced mechanical properties as compared to the unfilled versions. The tensile strength, modulus and tear strength of the elastomers are tunable by changing the filler content. Further study on the filler reinforcing mechanism suggests that both the polymer-filler interactions and the filler-filler interactions play key roles in the mechanical property enhancement.
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    A metathesis route to light harvesting polymers for organic solar cells
    (2013-05) Speros, Joshua Cole
    Conjugated polymers (CPs), macromolecules consisting of alternating single and double bonds, are of tremendous interest to the scientific community considering their applications in field-effect transistors, light-emitting diodes, sensors, and organic photovoltaics (OPVs). OPVs are an area of particular interest because cost-effective solution processing techniques can be employed to prepare flexible large-area light harvesting devices. In addition, light absorption and charge transport characteristics may be tuned by synthetically altering the CP scaffold. This dissertation describes the synthesis of a variety of CPs prepared by acyclic diene metathesis (ADMET) polymerization using versatile ruthenium-based Grubbs catalysts. All polymers were based on the low band gap poly(thienylene vinylene) (PTV) scaffold. The influence of polymer molecular weight, composition, and repeat unit architecture on both individual polymer behavior and OPV performance was investigated systematically.