On Sustainable Vitrimers Based on Polycaprolactones

Vitrimers represent an environmentally friendly class of materials, which behave like thermosets at room temperature but exhibit thermoplastic flow behavior when heated, making them processable and recyclable, thus extending material life and reducing waste. However, to fully meet the current demand for a sustainable economy, biodegradability at the end of the material life should also be considered, a property that not all vitrimers possess. Based on the above issues, this work aimed to develop biodegradable vitrimers based on polycaprolactone (PCL), a biodegradable polyester potentially derived from biomass fermentation. In detail, three different ad hoc synthesized star-shaped acrylated PCLs, characterized by different number of arms and molecular weight, were synthesized and used to prepare vitrimeric systems. Indeed, the above polymers were cross-linked with a fast exchangeable diboronic ester dithiol (2,2′-(1,4-phenylene)-bis[4-mercaptan-1,3,2-dioxaborolane], DBEDT), in solventless conditions. The formation of a dynamic network was proven by Fourier transform infrared, differential scanning calorimetry, thermogravimetric analysis, gel fraction, rheological, and dynamic mechanical analyzer measurements. In particular, the activation energies for the relaxation process of these materials were verified by rheological measurements in the range 44–62 kJ/mol. Moreover, all vitrimers, which were completely degraded by enzymatic hydrolysis within 12 days, exhibited excellent recyclability and self-healing properties when heated to 180 °C before processing.