New bio-based materials obtained by thiol-ene/thiol-epoxy dual curing click procedures from eugenol derivates

Abstract

Novel bio-based and dual-curable thermosets were prepared from eugenol derivatives. The curing sequence combined two click reactions, a photoinduced radical thiol-ene reaction followed by a thermally activated thiol-epoxy reaction.\ud Eugenol was transformed into a triallyl (3A-EU) and a diallyl glycidyl derivative (2AG-EU) with high yields, and they were used as starting monomers in order to study the thiol-ene reaction and the dual-curing process, respectively. Three different thiol crosslinkers were tested, one commercially available tetrathiol derived from pentaerythritol (PETMP) and two other that were also synthesized: a trithiol derived from eugenol (3SH-EU) and a hexathiol derived from squalene (6SH-SQ).\ud \ud FTIR and DSC were used to monitor both curing stages and analyze the obtained materials. The results evidenced the occurrence of side reactions that led to incomplete thiol-ene reaction. The dual-curable materials showed higher Tgs than the materials obtained by a simple thiol-ene process and presented higher mechanical and thermomechanical performance.Postprint (author's final draft

Preparation of new biobased coatings from a triglycidyl eugenol derivative through thiol-epoxy click reaction

“…In a previous study, 34 triallyl eugenol (3A-EU) was photocured through thiol-ene reaction with the same thiols selected in the present study and the T g s of the materials obtained were very low, between 1 and 14 °C. In the same study, the combination of thiol-ene and thiol-epoxy reaction of the diallyl glycidyl eugenol with the same tiols allowed to increase the T g s up to 28-57 °C, which was attributed to the better behavior of thiol-epoxy processes.…”

“…This compound was described in a previous publication. 34 The viscous liquid product was obtained with high yield and purity and its structure confirmed by spectroscopic measurements. The hexathiol derived from squalene (6SH-SQ) was prepared by the same synthetic methodology (thiol-ene/saponification) as reported before.…”

“…The synthesis was performed as previously reported by us. 34 The synthetic procedure starts from triallyleugenol (3A-EU) that was irradiated with thioacetic acid (TAA) in the presence of DMPA. The thioacetate was saponified with a methanol solution of NaOH.…”

“…The hexathiol derived from squalene (6SH-SQ) was prepared by the same synthetic methodology (thiol-ene/saponification) as reported before. 36,34…”

“…32,33 In a previous study of our group we put into evidence that thiol-epoxy reaction is highly advantageous in front of thiol-ene processes to obtain crosslinked materials from eugenol derivatives. 34 Yoshimura et al proposed the preparation of networks from triallyl eugenol by thiol-ene processes but the maximum T g s reached for the materials were not higher than 9.1 ºC.7 On substituting an allyl by a glycidyl group we increased the T g in more than 25 °C by the higher efficiency of the thiol-epoxy process compared to the thiol-ene in eugenol substrates.…”