Toward flame-retardant, transparency, and high mechanical property of polycarbonate based on low addition of linear polyborosiloxane

Functionalization and high performance of polycarbonate (PC) is hardly achieved by using traditional flame retardants, which will improve the flame retardancy of PC at the expense of mechanical strength, thermal stability and transparency. Herein, a linear macromolecular of polydiphenyl phenyl borosiloxane (PDPBS) was synthesized by dehydration polycondensation in order to solve the conflict between fire safety and high performance of PC. Due to the role of PDPBS in catalyzing char formation and helping to form dense char layer during the combustion process of PC composites, and the outstanding flexibility of siloxane segments with excellent compatibility with PC matrix, PC/PDPBS composites can maintain almost the same transparency as that of PC and obtain excellent flame retardancy. The results of burning tests showed that the PC composites with 3 wt% PDPBS passed the UL 94V-0 rating with a LOI value of 29.1%. Meanwhile, the peak of heat release rate (PHRR) and total heat release rate (THR) of PC/PDPBS-3 decreased by 12% and 15% respectively, and the ignition time (TTI) increased by 9%. More importantly, the PC/PDPBS-3 composite maintains a transparency at 87.5%. In addition, the tensile strength and elongation at break remained at the same level as that of neat PC. In a word, the addition of PDPBS can not only improve the flame retardancy of PC, but also keep its outstanding transparency and excellent mechanical properties. This work provides a new method for obtaining PC with both flame retardant and transparent properties, and also broadens the application of PC in electronic appliances and automobiles.