Simultaneous Improvement of Mechanical and Fire-Safety Properties of Polymer Composites with Phosphonate-Loaded MOF Additives

Flame-retardant (FR) additives are commonly used to improve the fire safety of synthetic polymers, which are widely employed in manufactured consumer goods. Incorporation of an FR in a polymer typically leads to deterioration of its mechanical properties. It also manifests itself in non-negligible volatile organic compound (VOC) release, which in turn increases environmental risks carried by both the application and disposal of the corresponding consumer goods. Herein, we present a hierarchical strategy for the design of composite materials, which ensures simultaneous improvement of both mechanical and fire-safety properties of polymers while limiting the VOC release. Our strategy employs porous metal–organic framework (MOF) particles to provide a multifunctional interface between the FR molecules and the polymer. Specifically, we demonstrate that the particles of environmentally friendly HKUST-1 MOF can be infused by a modern FRdimethyl methylphosphonate (DMMP)and then embedded into widely used unsaturated polyesters. The DMMP–HKUST-1 additive endows the resulting composite material with improved processability, flame retardancy, and mechanical properties. Single-crystal X-ray diffraction, thermogravimetric analysis, and computational modeling of the additive suggest the complete pore filling of HKUST-1 with DMMP molecules being bound to the open metal sites of the MOF.阻燃（Flame-retardant, FR）添加剂是提升合成聚合物防火安全性的常用助剂，而合成聚合物广泛应用于各类消费品中。将阻燃剂掺入聚合物基体通常会导致其力学性能劣化，同时还会引发不容忽视的挥发性有机化合物（volatile organic compound, VOC）释放，进而提升相关消费品在使用与处置环节的环境风险。本研究提出一种用于复合材料设计的分级策略，可在限制VOC释放的同时，同步改善聚合物的力学性能与防火安全性能。该策略借助多孔金属有机框架（metal–organic framework, MOF）颗粒，在阻燃剂分子与聚合物之间构建多功能界面。具体而言，本研究证实，环境友好型HKUST-1金属有机框架颗粒可负载新型阻燃剂——甲基膦酸二甲酯（dimethyl methylphosphonate, DMMP），随后将其嵌入广泛使用的不饱和聚酯基体中。该DMMP–HKUST-1复合助剂可赋予所得复合材料更优异的加工性能、阻燃性能与力学性能。对该助剂的单晶X射线衍射、热重分析与计算模拟结果表明，HKUST-1的全部孔道均被DMMP分子填充，且DMMP与该MOF的开放金属位点相结合。