Robust and Direct Route for the Development of Elastomeric Benzoxazine Resins by Copolymerization with Amines

The development of soft pressure sensors, in particular electronic skin, is fundamental to the interfacing between the human body and the outside world, namely, in prosthetics and biomedical applications. In this context, hybrid composite materials incorporating electrically conducting 2D flakes in an insulating matrix show attractive tunable piezoresistive properties suitable for wide-range pressure sensing applications. Here, we report on the design of novel trifunctional benzoxazine precursors for this polymer matrix based on tris(3-aminopropyl)amine and phenol reagents. These precursors have been successfully synthesized and copolymerized with polyetheramines of different lengths to tune the thermomechanical properties of the resulting networks. Extensive molecular dynamics simulations unambiguously relate the changes in glass transition temperature with chemical composition to the variations in the cross-link density and provide Tg values in excellent agreement with the experimental data. With the longest polyetheramine (2000 g mol-1), we achieve the synthesis of an elastomeric benzoxazine exhibiting remarkably low Tg of -41 °C, a modulus in compression of 50 kPa, and a shear strain modulus of 300 Pa, with high potential for low-pressure sensing applications.