High service temperature, self-mendable thermosets networked by isocyanurate rings

Abstract

A new mending chemistry exhibiting stability at extreme temperatures and holding mechanical properties as well as mechanical stability comparable to widely used engineering plastics is reported here. This mendable thermoset polymer is synthesized using commodity reactants through the formation of a isocyanurate-oxazolidone network which exhibit a high service temperature as shown by their T g of 270°C and T d of 365°C. We demonstrate that this network polymer is repeatedly self-mendable in the presence of a macroscopic crack, yielding considerable recovery of the polymer's strength after thermal annealing. This self-mending behavior is derived from a high density of mechano-responsive isocyanurate rings which are introduced as cross-links in the network. After mechanically initiated cycloreversion, the recovery of isocyanurate rings in a solid state is thermally initiated. This research is the first demonstration of an isocyanurate ring as a repairing moiety. We developed a new class of intrinsic self-mendable polymers withstanding high temperatures, which will greatly impact the application of thermoset polymers in the field of structural laminates and electronics packaging.

Isocyanurate transformation induced healing of isocyanurate–oxazolidone polymers

“…The chemical composition of the product under different reaction temperatures was investigated. As shown in Figure 2, the FTIR spectrum of the product after an 80 °C reaction shows the formation of isocyanurate (absorption band corresponding to the stretching CO vibration at 1710 cm −1 ) at this temperature, while no oxazolidone was detected (absorption band corresponding to the stretching CO vibration at 1750 cm −1 ) . When the reaction temperature was further increased to 150 °C, oxazolidone formed while the isocyanurate disappeared, as shown by the FTIR spectrum, indicating the isocyanurate‐to‐oxazolidone transformation at this elevated temperature.…”

“…For bulk polymerization of the ISOX polymers with nucleophiles such as tertiary amines, previous studies have shown agreement on the main reactions proceeding in the order of increased temperatures during the polymerization: (1) trimerization of isocyanate to isocyanurate, (2) oxazolidone formation from isocyanate and epoxide reaction, and (3) transformation of isocyanurate to oxazolidone through reaction with excessive epoxide . The isocyanurate and oxazolidone rings lead to a dense polymer network with a reported small molecular weight between crosslinks of 79 g/mol …”

“…Recently, ISOX polymers catalyzed by a tertiary amine N , N ‐dimethylbenzylamine (BDMA) have been discovered as a novel intrinsic self‐healing material . Microscopic and macroscopic cracks introduced into the polymers have been effectively and repeatably healed under thermal stimulus, without additional reactants or catalyst . The ISOX polymers were later shown to act as a self‐healable matrix in carbon fiber reinforced polymer composites, demonstrating repeatable elimination of matrix delamination induced by interlaminar shear .…”

“…4,5,13 The isocyanurate and oxazolidone rings lead to a dense polymer network with a reported small molecular weight between crosslinks of 79 g/mol. 14 properties. 15,16 The aromatic isocyanurate can withstand high temperatures up to 417 C and aromatic oxazolidone is stable up to 348 C, 17 thus explaining their wide usage for improving hightemperature resistance and flame retardancy of polyurethanes.…”

Prospects and Future Directions of Self-Healing Fiber-Reinforced Composite Materials

“…In terms of reversibility, the majority of healing substances are classified as thermoplastic. A mendable thermoset polymer with a glass transition temperature (T g ) of 270 • C and decomposition temperature (T d ) of 365 • C was synthesized by Zhang et al [28]. The isocyanurate-oxazolidone polymer incorporated with mechano-responsive isocyanurate rings recovers its broken bonding by means of thermal annealing.…”