We report here the synthesis and polymerization of a novel disubstituted valerolactone, β-acetoxy-δ-methylvalerolactone, derived from the renewable feedstock triacetic acid lactone (TAL). The bulk polymerization proceeds to 45% equilibrium monomer conversion at room temperature using diphenyl phosphate as the organic catalyst. The resultant amorphous material displays a glass transition temperature of 25 °C. The ring opening polymerization (ROP) behavior of the disubstituted valerolactone was examined, and the enthalpy () and entropy *() of polymerization were calculated to be −25 ± 2 kJ mol −1 and −81 ± 5 mol −1 K −1 , respectively. The polymerization kinetics were also measured and compared to those of other substituted valerolactones reported in the literature. This report is the first to demonstrate the successful ROP of a disubstituted valerolactone as well as the first to establish the ROP of a derivative of TAL.
more »
« less
Lactone Ring-Opening Equilibria in Methanol by 1H NMR Analysis: An Assessment of the Ring-Opening Polymerizability of Lactone Monomers
The purpose of this study was to learn if a convenient 1H NMR method could be developed to serve as a tool for estimating the propensity of a given lactone to participate in ring-opening transesterification polymerization (ROTEP). The methanolysis of each of 18 lactones was initially examined in CD3OD solution in the presence of sulfuric acid as a Brønsted catalyst at ambient temperature. Once equilibrium was established, the ratio of remaining lactone to the ring-opened methyl ester/alcohol could be readily measured by NMR spectroscopy. The observed thermodynamic driving force observed for the methanol ring openings is roughly in line with the extent of ROTEP for the various classes of lactones. This is the case even though the reaction conditions for these methanolyses versus ROTEP reactions are substantially different. Qualitative evaluations of the rates of the ring-opening methanolyses were also performed, and several non-obvious relative reactivities were observed. Finally, employing this simple NMR methanolysis using low concentrations of methanol in CDCl3 is recommended as the preferred protocol for the initial evaluation of the polymerizability of any new lactone monomer that researchers may prepare in the future.
more »
« less
- Award ID(s):
- 1901635
- NSF-PAR ID:
- 10394658
- Date Published:
- Journal Name:
- Macromolecules
- ISSN:
- 0024-9297
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract A depolymerizable vitrimer that allows both reprocessability and monomer recovery by a simple and scalable one‐pot two‐step synthesis of vitrimers from cyclic lactones is reported. Biobased
δ ‐valerolactone with alkyl substituents (δ ‐lactone) has low ceiling temperature; thus, their ring‐opening‐polymerized aliphatic polyesters are capable of depolymerizing back to monomers. In this work, the amorphous poly(δ ‐lactone) is solidified into an elastomer (i.e.,δ ‐lactone vitrimer) by a vinyl ether cross‐linker with dynamic acetal linkages, giving the merits of reprocessing and healing. Thermolysis of the bulkδ ‐lactone vitrimer at 200 °C can recover 85–90 wt% of the material, allowing reuse without losing value and achieving a successful closed‐loop life cycle. It further demonstrates that the new vitrimer has excellent properties, with the potential to serve as a biobased and sustainable replacement of conventional soft elastomers for various applications such as lenses, mold materials, soft robots, and microfluidic devices. -
Lactones are cyclic esters with extensive applications in materials science, medicinal chemistry, and the food and perfume industries. Nature’s strategy for the synthesis of many lactones found in natural products always relies on a single type of retrosynthetic strategy, a C−O bond disconnection. Here, we describe a set of laboratory-engineered enzymes that use a new-tonature C−C bond-forming strategy to assemble diverse lactone structures. These engineered “carbene transferases” catalyze intramolecular carbene insertions into benzylic or allylic C−H bonds, which allow for the synthesis of lactones with different ring sizes and ring scaffolds from simple starting materials. Starting from a serine-ligated cytochrome P450 variant previously engineered for other carbene-transfer activities, directed evolution generated a variant P411-LAS-5247, which exhibits a high activity for constructing a five-membered ε-lactone, lactam, and cyclic ketone products (up to 5600 total turnovers (TTN) and >99% enantiomeric excess (ee)). Further engineering led to variants P411-LAS-5249 and P411-LAS-5264, which deliver six-membered δ-lactones and seven-membered ε-lactones, respectively, overcoming the thermodynamically unfavorable ring strain associated with these products compared to the γ-lactones. This new carbene-transfer activity was further extended to the synthesis of complex lactone scaffolds based on fused, bridged, and spiro rings. The enzymatic platform developed here complements natural biosynthetic strategies for lactone assembly and expands the structural diversity of lactones accessible through C−H functionalization.more » « less
-
Strained cycloalkynes are of considerable interest to theoreticians and experimentalists, and possess much synthetic value as well. Herein, a series of cyclic alkylidenecarbenes—formally obtained by replacing the carbonyl oxygen of four-, five-, and six-membered lactams, lactones, and thiolactones with a divalent carbon—were modeled at the CCSD(T)/cc-pVTZ//B3LYP/6-311+G** and CCSD(T)/cc-pVTZ//CCSD/6-311+G** levels of theory. The singlet carbenes were found to be more stable than the triplets. The strained heterocyclic alkynes formed by ring expansion of these singlet carbenes were also modeled. Interestingly, the C≡C bonds in the five-membered heterocycles, obtained from the rearrangement of β-lactam- and β-lactone-derived alkylidenecarbenes, displayed lengths intermediate between formal double and triple bonds. Furthermore, 2-(1-azacyclobutylidene)carbene was found to be nearly isoenergetic with its ring-expanded isomer, and 1-oxacyclopent-2-yne was notably higher in energy than its precursor carbene. In all other cases, the cycloalkynes were lower in energy than the corresponding carbenes. The transition states for ring-expansion were always lower for the 1,2-carbon shifts than for 1,2-nitrogen or oxygen shifts, but higher than for the 1,2-sulfur shifts. These predictions should be verifiable using carbenes bearing appropriate isotopic labels. Computed vibrational spectra for the carbenes, and their ring-expanded isomers, are presented and could be of value to matrix isolation experiments.more » « less
-
null (Ed.)A dimeric yttrium phenoxide complex supported by a ferrocene Schiff base ligand, [(salfen)Y(OPh)] 2 (salfen = ( N,N ′-bis(2,4-di- tert -butylphenoxy)-1,1′-ferrocenediimine), was synthesized and characterized. According to electrochemical studies and 1 H NMR spectroscopy, [(salfen)Y(OPh)] 2 can be oxidized in a stepwise fashion to access three oxidation states. The catalytic activity of the three states toward the ring opening polymerization of cyclic esters and epoxides was investigated. The activity toward cyclic esters decreases upon oxidation while the opposite trend was observed in epoxide polymerization. Block copolymer syntheses using a redox switch were also performed.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.macromol.2c01141
