Preparation and Characterization of a Series of Self-Healable Bio-Based Poly(thiourethane) Vitrimer-like Materials

Abstract

A series of poly(thiourethanes) (PTUs) from biobased monomers have been synthesized. Limonene and squalene were transformed into polyfunctional thiols by thiol-ene reaction with thioacetic acid and further saponification. They were then reacted in different proportions with hexamethylene diisocyanate (HDI) in the presence of a catalyst to prepare bio-based poly(thiourethane) vitrimer-like materials. The different functionalities of squalene and limonene thiols (six and two, respectively) allow for changing the characteristics of the final material by only varying their relative proportions in the reactive mixture. The proportions of thiol and isocyanate groups were stoichiometric in all the formulations tested. An acidic and a basic catalyst were tested in the preparation of the networked polymers. As the acidic catalyst, we selected dibutyltin dilaurate (DBTDL), and as the basic catalyst, a tetraphenylborate salt of 1,8-diazabicyclo(5.4.0)undec-7-ene (BGDBU), which has the advantage of only releasing the base at high temperatures. The materials obtained were characterized by thermogravimetry and thermomechanical analysis. The vitrimeric-like behavior was evaluated, and we could see that higher proportions of the limonene derivative in the formulations led to faster stress relaxation of the material. The use of the base catalyst led to a much shorter relaxation time. The materials obtained demonstrated good self-healing efficiency.

Revealing Dynamic Behavior in High Dielectric Poly(thiourethane)-Based Vitrimer-like Materials

“…Over the past few years, Serra and co-workers − ,, have shown that these materials exhibit vitrimeric-like behavior, characterized by the dissociation of the thiourethane group into isocyanate and thiol. This process is followed by rapid reformation, resulting in a decrease in viscosity upon heating, following an Arrhenius-type evolution.…”

“…PTUs are synthesized through the condensation of isocyanates and thiols, resulting in materials with dynamic properties facilitated by thiourethane–thiourethane or thiol–thiourethane exchange reactions . Since the initial report in 2019 by Torkelson’s group, various thiol–isocyanate systems with dynamic properties have been investigated, employing different catalysts and exploring sustainable alternatives. − In the quest for more sustainable materials, there have been reports on substituting monomers derived from biomass for those derived from fossils, along with the development of non-isocyanate poly­(thiourethane)­s (NIPTUs). , Additionally, dynamic PTUs have been employed as a polymeric matrix in nanocomposites …”

Latent catalysts in vitrimers

“…For this, Guerrero et al employed 9 that facilitates the thermal decomposition of the imidazolium salt at temperatures above 100 °C. 17 This process results in the liberation of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), which serves as a basic catalyst for the transthiocarbamoylation exchange reaction. 17,33…”

“…17 This process results in the liberation of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), which serves as a basic catalyst for the transthiocarbamoylation exchange reaction. 17,33…”

“…This activation can be triggered by several stimuli, including heat and light. 10–20 It should be facile and cost-effective to prepare and demonstrate a high level of reactivity after activation. Latent catalysts have been employed in CANs, allowing for precise manipulation of exchange reactions.…”