Research ArticleAPPLIED SCIENCES AND ENGINEERING

A coating from nature

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Science Advances  16 Dec 2020:
Vol. 6, no. 51, eabe0026
DOI: 10.1126/sciadv.abe0026
  • Fig. 1 Design of bio-based alternatives for acrylates and coatings.

    (A) General strategy for bio-based alternatives instead of common petrochemical-based acrylate monomers to yield coatings. (B) Photooxidation of the biomass-derived furfural followed by derivatization toward alkoxybutenolide monomers comprising an acrylate type structure (acrylate unit is shown in pink).

  • Fig. 2 Upscaling of the photooxidation of furfural.

    (A) Reaction of furfural with singlet oxygen catalyzed by the photosensitizer methylene blue (shown in box) yielding hydroxybutenolide B1. (B) Rotary evaporator photoreactor setup scheme (left); picture of rotary thin-film system in operation (right) using a 10 × 80–W white light LED setup (see the Supplementary Materials pages S5 and S6 for experimental details and photoreactor setup, and table S1 for full optimization details). (C) Flow photooxidation setup scheme (left) and picture of five parallel flow systems in operation (right). A detailed description of the experimental setup and optimization can be found in fig. S4 and table S2. Photo credit (B and C): J. G. H. Hermens, University of Groningen.

  • Fig. 3 Homo- and copolymerization of alkoxybutenolide.

    (A) Reaction scheme, structures of (co)monomers, and conversions. General (co)polymerization reaction, reaction conditions: butenolides-comonomers (1:1 ratio), Trigonox 42S (6 mol %), 2.15 M in 1-methoxy-2-propanol, reflux, 50 min to 4 hours. (B) Substrate conversion of alkoxybutenolides, homopolymerization (column 1), and copolymerization (columns 2 to 4); butenolides-comonomers (1:1 ratio), in the case of di(ethylene glycol) divinyl ether 1:0.5 ratio. (A) Maximum conversion obtained for copolymerization of B2, DVE and B4, DVE due to formation of insoluble material. For a complete overview of copolymerization reactions, see table S38.

  • Fig. 4 Reaction kinetics of the copolymerization of B2 with VeoVa-10.

    (A) Copolymerization of methoxybutenolide B2 with VeoVa-10 (1:1 ratio), followed by 1H NMR spectroscopy using 1,3,5-trimethoxybenzene (0.5 eq.) as internal standard, reaction conditions: Trigonox 42S (6 mol %), 2.15 M in 1-methoxy-2-propanol, reflux, 2 hours. (B) 1H NMR signals over time by taking samples and flash freezing (−18°C) them at certain timestamps. (C) Concentration of monomers over time during the copolymerization of B2 with VeoVa-10. (D) Conversion of polymer BP2 over time. (E) Rate of copolymerization of B2 and VeoVa-10. (For full kinetic analysis of all copolymerizations, see also figs. S10 to S143, tables S4 to S38, and the Supplementary Materials pages S30 to S210.). ppm, parts per million.

  • Fig. 5 Rate of (co)polymerization B2 to B5 with comonomer.

    ( Homopolymerization of B2 to B5 (2 eq.) and copolymerizations of B2 to B5 with comonomers VeoVa-10 (1:1 ratio), dodecyl vinyl ether (1:1 ratio), and di(ethylene glycol) DVE (1:0.5 ratio), reaction conditions: Trigonox 42S (6 mol %) (3 mol % in case of homopolymerization), 2.15 M in 1-methoxy-2-propanol (4.3 M in case of homopolymerization), reflux, 6 min to 4 hours. Rate of polymerization [ln(1/(1 − U)] as a function of t where U = conversion of polymer. (A) Rates of homopolymerization methoxybutenolide (BP1), hexyloxybutenolide (HP1), isopropoxybutenolide (IP1), and menthyloxybutenolide (MP1). (B) Rate of copolymerization of VeoVa-10 with methoxybutenolide (BP2), hexyloxybutenolide (HP2), isopropoxybutenolide (IP2), and menthyloxybutenolide (MP2). (C) Rates of copolymerization of dodecyl vinyl ether with methoxybutenolide (BP3), hexyloxybutenolide (HP3), isopropoxybutenolide (IP3), and menthyloxybutenolide (MP3). (D) Rate of copolymerization of di(ethylene glycol) DVE with methoxybutenolide (BP4), hexyloxybutenolide (HP4), isopropoxybutenolide (IP4), and menthyloxybutenolidebutenolide (MP4) (see also table S38).

  • Fig. 6 Inhibition after the addition of presynthesized copolymer MP2.

    Reaction conditions: Trigonox 42S (6 mol %), 2.15 M in 1-methoxy-2-propanol, reflux, 4 hours. Inhibited polymerization of menthyloxybutenolide B5 with VeoVa-10 (1:1 ratio, cyan line) at 92% conversion, t = 9000 s. Polymerization of menthyloxybutenolide B5 with VeoVa-10 (1:1 ratio, dark blue line) until t = 1800 s. Inhibited polymerization of menthyloxybutenolide B5 with VeoVa-10 after the addition of presynthesized menthyloxybutenolide–VeoVa-10–copolymer MP2 (1 ml of 2.15 M solution in 1-methoxy-2-propanol, 92% conversion) (1:1 ratio, blue line) at t = 2400 s. Similar reaction rates are obtained, k2obsbefore = 5.0·105 s1 and k2obsafter = 2.6·105 s1, for the inhibited polymerization at t = 9000 s (cyan line) and the induced inhibited polymerization at t = 2400 s (blue line). For further elucidation of this polymerization behavior, control experiments, and kinetic data and analysis, see the Supplementary Materials pages S179 to S209.

  • Fig. 7 Coating formation of alkoxybutenolides.

    (A) General cross-linking reaction of alkoxybutenolides (1 eq.) with DVE (0.5 eq.), Omnirad 819 (3 mol %) as radical initiator and UV light (λirr = 395 nm, 5 min) as trigger. Coating coding: BP4 = B2 (methoxy-) + DVE, HP4 = B3 (hexyloxy-) + DVE, IP4 = B4 (isopropoxy-) + DVE, MP4 = B5 (menthyloxy-) + DVE. (B) Through (1) mixing alkoxybutenolide B2 to B5 with DVE and Omnirad 819 until a homogeneous mixture is obtained, (2) applying the mixture uniformly on a glass plate (100 μm) using a Byk applicator, and (3) irradiating the glass plate for 5 min with UV light (λirr = 395 nm), (4) a hard transparent butenolide-based coating is formed. For figures of butenolide coatings on glass plates, see figs. S167 to S172. Photo credit (B): R. van Gemert, AkzoNobel Car Refinishes BV.

  • Fig. 8 Butenolide coatings and properties.

    Coating formation conditions: Alkoxybutenolide B2 to B5 (1 eq.), di(ethylene glycol) DVE (0.5 eq.) Omnirad 819 (3 mol %), UV light (λirr = 395 nm), 5 min. (A) Clear, uniform, and hard methoxybutenolide coating BP4 on glass (100 μm). (B) Methoxybutenolide coating BP4 subjected to standardized spot tests, droplet of water removed after 1 hour, droplet of 2-butanone [methyl ethyl ketone (MEK)] removed after 1 min. Water has no effect on coating, resulting in no visible defects. MEK has a minor effect on coating, resulting in very slight discoloring. (C) Clear, uniform, and hard hexyloxybutenolide coating HP4 on glass (100 μm). (D) Clear, uniform, and hard hexyloxybutenolide coating HP4 on polypropylene (100 μm). Photo credit (A to D): R. van Gemert, AkzoNobel Car Refinishes BV. (E) Summary of the properties of the various alkoxybutenolide coatings. aWater/MEK resistance, 0 = damaged coating, 5 = no damage, general procedure in the Supplementary Materials page S240. b23 weight % of butyl acetate was added to dissolve the monomers. cVeoVa-10 added for increasing hydrophobicity to coat on polypropylene, butenolide/DVE/VeoVA-10—2/0.7/0.6 equiv. ND, not determined (Supplementary Materials pages S240–S242). For all coatings on glass plates, see the Supplementary Materials pages S234–S239; for DMTA, see the Supplementary Materials pages S241–S247; and for BP4, IP4, and MP4 coated on polypropylene, see figs. S168 to S171.

  • Table 1 Justification of the principles of green chemistry.

    Relevant Principles of Green Chemistry and analysis for the synthesis of alkoxybutenolide monomers from furfural.

    Principles of Green ChemistryJustification
    Less hazardous chemical synthesisIn the synthesis, starting from the platform chemical furfural, benign solvents (methanol and toluene) are used for the preparation of alkoxybutenolides. As vacuum distillation is used as the purification method, no other environmentally hazardous solvents are used.
    Design for energy efficiencyThe oxidation of furfural is performed photochemically (visible light) at ambient temperature. Scalable photooxidation procedures with energy-efficient lamps (TL and LED) have been designed.
    Use of renewable feedstocksFurfural, a platform chemical derived from the acid-mediated dehydration of lignocellulose (H2O as waste), is used as sole starting material for the synthesis of alkoxybutenolides (45, 46).
    Reduce derivativesThe hemiacetal moiety in hydroxybutenolide B1 allows facile derivatization toward alkoxybutenolides without the use of protecting/activation groups.
    CatalysisThe oxidation of furfural is photocatalytic using molecular oxygen, preventing the use of stoichiometric amounts of oxidants.
    Inherently safer chemistry for accident preventionThe flow reactor designed for the upscaling of the photooxidation of furfural allows a safer handling of reactive substrates (pressurized oxygen) or intermediates (endoperoxide) as low concentrations, and no accumulation is present in flow (30).
  • Table 2 Properties of butenolide polymers.

    Polymer properties of alkoxybutenolide-based polymers BP2, BP3, HP2, HP3, IP2, IP3, MP2, and MP3 and butyl acrylate polymers homopolymer BAP1 and copolymer with VeoVa-10 BAP2 for comparison; molecular weights, length, and glass transition temperature (Tg).

    Polymer*Monomer 1Monomer 2Mn (g/mol)Mw (g/mol)DnTg (°C)
    BP2Embedded ImageEmbedded Image11652,7892.398.9312
    BP3Embedded ImageEmbedded Image16114,8823.0314.69−62
    HP2Embedded ImageEmbedded Image12423,2642.638.54−27
    HP3Embedded ImageEmbedded Image15484,5872.9611.57−72
    IP2Embedded ImageEmbedded Image15723,1742.029.3212
    IP3Embedded ImageEmbedded Image17644,2952.4312.12−67
    MP2Embedded ImageEmbedded Image11513,1012.697.1124
    MP3Embedded ImageEmbedded Image15844,7112.9710.4616
    BAP1Embedded Image/402215,8603.94123.72−39
    BAP2Embedded ImageEmbedded Image280610,7663.8433.00−50

    *Reaction conditions: 1:1 ratio of monomers, Trigonox 42S (6 mol %), 2.15 M in 1-methoxy-2-propanol, reflux, 10 min to 4 hours.

    †Polydispersity (D) is calculated by dividing Mw by Mn.

    ‡Average amount of units in the polymer chain (n) is calculated through dividing number average molecular weight (Mn) by average mass of unit (mass monomer 1 + mass monomer 2).

    Supplementary Materials

    • Supplementary Materials

      A coating from nature

      Johannes G. H. Hermens, Thomas Freese, Keimpe J. van den Berg, Rogier van Gemert, Ben L. Feringa

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