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Issue 9, 2014
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Bringing D-limonene to the scene of bio-based thermoset coatings via free-radical thiol–ene chemistry: macromonomer synthesis, UV-curing and thermo-mechanical characterization

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Abstract

The increasing pursuit for bio-based plastic materials led us to investigate the potential use of the monoterpene limonene in thermoset synthesis using the free-radical mediated thiol–ene reaction. The high efficiency of this reaction to prepare multifunctional ene-terminated resins, as intermediary macromolecular precursors, for thermosets synthesis was demonstrated under thermal and photoinitiated conditions. Although an excess of terpene favors formation of well-defined macromonomers in organic solution, the characteristic low-vapor pressure of limonene hinders its simple removal (or recycling) via evaporation after synthesis. Alteration to an initial thiol–ene stoichiometry of 1 : 0.5 enables production of high molecular weight resins in the form of ‘hyperbranched oligomeric-like’ structures having moderate polydispersity. UV-curing of these polyfunctional resins combined with equal mole compositions of multifunctional alkyl ester 3-mercapto propionates yields highly sticky, amorphous and flexible elastomers with different thermo-mechanical properties. These can be further modulated by varying the amount of unreacted thiol occluded within the networks working as a plasticizer. Introduction of a renewable cycloaliphatic structure into the materials offers a convenient way to enhance the glass-transition temperature and stiffness of traditional thiol–ene networks. The materials synthesized may be considered potentially useful as sealants and adhesives in a wide variety of applications including organic coatings. The versatility of UV-irradiation over thermal initiation makes this method particularly suitable for green industrial synthesis processes via thiol–ene chemistry using limonene and multifunctional thiols. The thiol–ene system evaluated herein serves as a model example for the sustainable incorporation of natural diolefinic monomers into semi-synthetic thiol–ene networks exhibiting a range of thermo-mechanical properties.

Graphical abstract: Bringing d-limonene to the scene of bio-based thermoset coatings via free-radical thiol–ene chemistry: macromonomer synthesis, UV-curing and thermo-mechanical characterization

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Publication details

The article was received on 18 Sep 2013, accepted on 28 Nov 2013 and first published on 02 Dec 2013


Article type: Paper
DOI: 10.1039/C3PY01302B
Polym. Chem., 2014,5, 3245-3260
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    Bringing D-limonene to the scene of bio-based thermoset coatings via free-radical thiol–ene chemistry: macromonomer synthesis, UV-curing and thermo-mechanical characterization

    M. Claudino, J. Mathevet, M. Jonsson and M. Johansson, Polym. Chem., 2014, 5, 3245
    DOI: 10.1039/C3PY01302B

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