Issue 9, 2014

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

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

Supplementary files

Article information

Article type
Paper
Submitted
18 Sep 2013
Accepted
28 Nov 2013
First published
02 Dec 2013
This article is Open Access
Creative Commons BY license

Polym. Chem., 2014,5, 3245-3260

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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