Preparation of Ar–P–N-structured flame retardant via Kabachnik–Fields reaction for fire safety and mechanical reinforcement of polyurethane

Abstract

Fire safety of polyurethanes (PUs) has limited their further practical applications. To address this problem, we designed novel phosphorus-based flame retardants (P-FR) by incorporating aryl (Ar) groups via Kabachnik–Fields reaction, realizing π–π interaction-reinforced Ar2 and Ar5. Total heat release and peak heat release rate of PU/Ar5, whose flame-retardancy-index of 5.02 due to reduced combustion time, decreased 23.24 and 9.23 %, respectively, compared with neat PU. Moreover, UL94 rating for PU/Ar5 was improved from V-2 to V-0. These results demonstrate that Ar5 effectively generate a barrier effect that blocks oxygen, fuel, and heat. Sluggish mobility and phase transition are responsible for such enhancement due to a delay effect with the existence of π–π interactions and steric hindrance. Encouragingly, tensile strength and toughness of PU/Ar5 were greatly improved by 1345.8 and 670.3 %, respectively, compared with neat PU. We believe that this study could provide a promising method for introducing specific function to flame retardants to enhance fire safety and mechanical properties of composites.