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

Do Carbon Nanotubes Improve the Thermomechanical Properties of Benzoxazine Thermosets?

Fillers are widely used to improve the thermomechanical response of polymer matrices, yet often in an unpredictable manner because the relationships between the mechanical properties of the composite material and the primary (chemical) structure of its molecular components have remained elusive so far. Here, we report on a combined theoretical and experimental study of the structural and thermomechanical properties of carbon nanotube (CNT)–reinforced polybenzoxazine resins, as prepared from two monomers that only differ by the presence of two ethyl side groups. Remarkably, while addition of CNT is found to have no impact on the glass-transition temperature (<i>T</i>_g) of the ethyl-decorated resin, the corresponding ethyl-free composite features a surge by ∼47 °C (50 °C) in <i>T</i>_g, from molecular dynamics simulations (dynamic mechanical analysis measurements), as compared to the neat resin. Through a detailed theoretical analysis, we propose a microscopic picture for the differences in the thermomechanical properties of the resins, which sheds light on the relative importance of network topology, cross-link and hydrogen-bond density, chain mobility, and free volume

Do Carbon Nanotubes Improve the Thermomechanical Properties of Benzoxazine Thermosets?

Fillers are widely used to improve the thermomechanical response of polymer matrices, yet often in an unpredictable manner because the relationships between the mechanical properties of the composite material and the primary (chemical) structure of its molecular components have remained elusive so far. Here, we report on a combined theoretical and experimental study of the structural and thermomechanical properties of carbon nanotube (CNT)–reinforced polybenzoxazine resins, as prepared from two monomers that only differ by the presence of two ethyl side groups. Remarkably, while addition of CNT is found to have no impact on the glass-transition temperature (<i>T</i>_g) of the ethyl-decorated resin, the corresponding ethyl-free composite features a surge by ∼47 °C (50 °C) in <i>T</i>_g, from molecular dynamics simulations (dynamic mechanical analysis measurements), as compared to the neat resin. Through a detailed theoretical analysis, we propose a microscopic picture for the differences in the thermomechanical properties of the resins, which sheds light on the relative importance of network topology, cross-link and hydrogen-bond density, chain mobility, and free volume

Tuning the Piezoresistive Behavior of Graphene-Polybenzoxazine Nanocomposites: Toward High-Performance Materials for Pressure Sensing Applications

Flexible piezoresistive pressure sensors are key components in wearable technologies for health monitoring, digital healthcare, human–machine interfaces, and robotics. Among active materials for pressure sensing, graphene-based materials are extremely promising because of their outstanding physical characteristics. Currently, a key challenge in pressure sensing is the sensitivity enhancement through the fine tuning of the active material’s electro-mechanical properties. Here, we describe a novel versatile approach to modulating the sensitivity of graphene-based piezoresistive pressure sensors by combining chemically reduced graphene oxide (rGO) with a thermally responsive material, namely, a novel trifunctional polybenzoxazine thermoset precursor based on tris(3-aminopropyl)amine and phenol reagents (PtPA). The integration of rGO in a polybenzoxazine thermoresist matrix results in an electrically conductive nanocomposite where the thermally triggered resist’s polymerization modulates the active material rigidity and consequently the piezoresistive response to pressure. Pressure sensors comprising the rGO-PtPA blend exhibit sensitivities ranging from 10–2 to 1 kPa–1, which can be modulated by controlling the rGO:PtPA ratio or the curing temperature. Our rGO-PtPA blend represents a proof-of-concept graphene-based nanocomposite with on-demand piezoresistive behavior. Combined with solution processability and a thermal curing process compatible with large-area coatings technologies on flexible supports, this method holds great potential for applications in pressure sensing for health monitoring