Browsing by Author "Wang, Yuanxian"

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    Supporting data for Primary data for Poly(4-ketovalerolactone) from Levulinic acid, Synthesis and Hydrolytic Degradation
    (2020-06-10) Xu, Shu; Wang, Yuanxian; Hoye, Thomas R; hoye@umn.edu; Hoye, Thomas R
    These files contain primary data along with associated output from instrumentation supporting all results reported in Xu et. al. Primary data for Poly(4-ketovalerolactone) from Levulinic acid, Synthesis and Hydrolytic Degradation. In Xu et al. we found: We report here the synthesis of poly(4-ketovalerolactone) (PKVL) via ring-opening transesterification polymerization (ROTEP) of the monomer 4-ketovalerolactone (KVL, two steps from levulinic acid). The polymerization of KVL proceeds to high equilibrium monomer conversion (up to 96% in the melt) to give the semicrystalline polyketoester PKVL with low dispersity. PKVL displays glass transition temperatures of 7 °C and two melting temperatures at 132 and 148 °C. This polyester can be chemically recycled through hydrolytic degradation. Under aqueous neutral or acidic conditions, the dominating pathway for polyester hydrolysis is through backbiting from the chain end. Under basic conditions, mid-chain cleavage, accelerated by the ketone carbonyl group in the backbone, promotes the hydrolysis of nearby backbone ester bonds. The final hydrolysis product is 5-hydroxylevulinic acid, the ring opened hydrolysis product of KVL. PKVL was also observed to degrade under the action of a Brønsted acid to a bis-spirocyclic dilactone natural product altaicadispirolactone, which is a dimer of KVL. This constitutes a rare example of a one-step synthesis of a secondary metabolite in which a polymer was the starting material and the sole source of matter. Analogous ROTEP of the isomeric 4-membered lactone 4-acetyl--propiolactone (APL) was also explored, although this chemistry was not as well-behaved as the KVL to PKVL polymerization.
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    Thermal Rearrangement Reactions of Polyynes and Preparation of Bio-renewable Monomers and Their Polymerizations
    (2018-06) Wang, Yuanxian
    Part I: This study explored several novel features of the hexadehydro-Diels-Alder (HDDA) reaction of substrates containing tethered trapping moieties. Three aspects are estiblished experimentally: i) Medium-sized fused rings can be produced by varying the length of the tether; ii) The tether can emanate (see red arc) from an atom within the linker unit that joins the 1,3-diyne and the diynophile; iii) The importance of the rate of trapping by the benzynophile is established. Part II: An unprecedented rearrangement reaction of alkynyl ynedione substrate is discovered, and the product of this process is butenolide-type compounds. The mechanism of this process has been thoroughly studied by both experimental and computational methods. Part III: The first conversion of α-methyleneglutaric anhydride to (a series of) α- methyleneglutarimides has been realized. These potentially bio-renewable monomers can then be polymerized to the corresponding polymers. These polymeric materials showed promising physical properties, including relatively high glass transition temperatures. The depolymerization process was also studied. Part IV: A ketolactone monomer has been made from bio-sourced levulinic acid via a simple and scalable process. The polymerization reaction of this monomer gives a novel class of polyester and the polyester showed a series of promising properties.