Browsing by Subject "Polyolefin"

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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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    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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    Mechanism and Application of a Heterogeneous Catalytic Hydrogen-deuterium Exchange Reaction for Polyolefins
    (2018-04) Zeng, Yiming
    The mechanism of a heterogeneous catalytic H/D exchange reaction with polyolefins is investigated in this thesis. The model polymers used in this study were hydrogenated polybutadienes (hPBDs), and a metallocene linear low density polyethylene (LLDPE). When mixed at 170 ºC with isooctane, Pt/Re-SiO2 catalyst, and gaseous deuterium, the polyolefins dissolve and undergo H/D exchange reaction at the surface of the catalyst, producing partially deuterium labelled polyolefins. Polymers with varying molecular weight, varying ethyl branch density and narrow molecular weight distribution were synthesized by anionic polymerization of 1,3-butadiene followed by saturation with gaseous hydrogen. The LLDPE polymer with relatively broader molecular weight distribution is a commercial product and was supplied by ExxonMobil Chemical Company. The extent of deuterium labelling is analyzed with density measurement, proton nuclear magnetic resonance spectroscopy (1H-NMR) and Fourier transform infrared (FTIR) spectroscopy. A size exclusion chromatography (SEC) instrument equipped with an IR detector was used to analyze the deuterium concentration within the LLDPE polymer as a function of molecular weight. Small angle neutron scattering (SANS) was conducted for both the pure labelled polyolefins and their blends. The partially labelled LLDPE sample was fractionated according to the molecular weight. The partially labelled fractions were blended with the normal LLDPE to create samples with different molecular weight portions labelled. These labelled blends were uniaxially stretched at room temperature while simultaneously monitored with SANS, providing a method to characterize the single chain alignment process at different stages of polyethylene deformation, as a function of time. In this thesis, several aspects of the isotope exchange reaction were investigated. We first examined the dependence of the isotope exchange on the molecular weight and branch content of the substrate polyolefins. The extent of isotope exchange was found to strongly favor the high molecular weight molecules. High branch concentration hinders the exchange reaction, but has a less impact at low branch content. These observations are best explained by viewing the exchange reaction as an absorption controlled process. The deuterium distribution was found to be inhomogeneous evidenced by both the SEC-IR and SANS results. From SANS results modeling, it was confirmed that mathematical accommodation of the inhomogeneous deuterium distribution is necessary to extract chain statistics. Finally, the in situ tensile-SANS experiments revealed that the single chains develop a high degree of alignment along the stretching direction during the elastic and plastic deformation processes of the LLDPE, and maintain that alignment during the strain hardening regime. A remarkable higher degree of chain alignment was found for the high molecular weight chains, a result of longer chains being able to form more tie chains between lamellae. The results of this work provided a scheme of analyzing commercial polyolefins on the single molecular scale, without the necessity to access the synthesis route of the materials.