Biobased, Biodegradable, Self-Healing Boronic Ester Vitrimers from Epoxidized Soybean Oil Acrylate

Abstract

The global production of thermosets has been increasing in recent years causing rapid consumption of fossil-based feedstocks and contributing to the plastic waste accumulation in the environment, especially because they cannot be easily reprocessed or recycled at the end of their lifetime. These drawbacks can only be overcome with the development of environmentally friendly, recyclable thermosets from renewable resources. For this reason, we present a facile way to produce a biobased reprocessable thermoset, a vitrimer, by thiol-acrylate coupling between epoxidized soybean oil acrylate and a diboronic ester dithiol dynamic cross-linker. The synthesis of the cross-linker and all the processes for the production of the vitrimer has been done following green chemistry principles. The developed vitrimer material can be reprocessed multiple times like a thermoplastic, without compromising its mechanical properties. Moreover, it can be conveniently recycled by reversible hydrolysis in 90% ethanol and subsequent solvent evaporation, regenerating the original vitrimer. An important advantage of the developed material, especially regarding its applications, is that it is able to self-repair mechanical abrasion-related defects, like scratches and cuts, at room temperature, thanks to the low glass transition temperature and rapid boronic ester exchange, which enables it to demonstrate great potential as a self-healing coating. In case of an accidental release into the environment, it is able to biodegrade, solving the problem of waste accumulation.

Fully Biobased Vitrimers: Future Direction toward Sustainable Cross‐Linked Polymers

“…[ 167 ] Up to date, two studies report the preparation of partially biobased vitrimers from fossil‐based 2,2’‐(1,4‐phenylene)‐bis[4‐mercaptan‐1,3,2‐dioxaborolane and a rosin‐based diepoxide or epoxidized soybean oil acrylate. [ 168,169 ] To the best of our knowledge, no study with higher renewable content was published.…”

Boronic Acid Esters and Anhydrates as Dynamic Cross-Links in Vitrimers

“…Thiol-ene addition, however thermally activated, has been utilized for the synthesis of soybean oil-based vitrimers. Zych et al [ 99 ] used a resin containing soybean oil acrylate and 2,2′-(1,4-phenylene)-bis[4-mercaptan-1,3,2-dioxaborolane] for the synthesis of a dynamic network by curing at 120 °C for 24 h. Due to the relatively low relaxation E a = 29 kJ/mol and low T g = 10.5 °C, the vitrimer exhibited healing properties at RT and could be easily remolded by hot-pressing at 120 °C. Furthermore, the authors did not observe the sample break during tensile testing even with extension rates as fast as 500 mm/min.…”

Rheological Characteristics of Cross-Linked Materials with Associative Bond Exchange Mechanisms

“…Depending on the cross-link density, the vitrimer sample had a T g of around 0 °C-10 °C. Despite the lack of T v information in their investigation, the boronic ester bond exchange is known to be active at room temperature or lower without the use of any catalysts 21,27) .…”