Controllable micro cross-linking towards multifunctional flame-retardant aliphatic polyamide

Constructing micro cross-linking structures into molecular chains has demonstrated the ability to improve basic properties, such as mechanical strength and thermal stability, of thermoplastic polymers. However, this method has limitations when it comes to improving the functionality of polymers. Herein, we reported a multifunctional micro cross-linking network that improves not just mechanical strength but also flame retardancy, dielectric properties, battery performance, antistatic properties, etc. A novel phosphinamide-containing monomer was designed, synthesized, and copolymerized into the polymer chain of polyamide 6, a typical thermoplastic polymer. On the one hand, the micro cross-linking structure was successfully obtained through the amide interchange reaction between the side-chain phosphinamide groups and the main-chain amide groups, leading to a 23.7% improvement of tensile strength and largely maintained tensile toughness. On the other hand, the functional phosphorus groups showed an efficient free-radical-capturing effect during fire, endowing the copolymer with excellent flame retardancy at a low monomer content of 2 mol%. Additionally, the copolymer also possessed great spinnability, melt-crystallization performance, as well as dielectric property, antistatic property, and battery performance, enabling its potential in a wide variety of applications.