Multi-functional ladderlike polysiloxane: synthesis, characterization and its high performance flame retarding bismaleimide resins with simultaneously improved thermal resistance, dimensional stability and dielectric properties

The development of high-performance flame-retardant polymers with simultaneously increased integrated performance, especially thermal resistance, dimensional stability and dielectric properties, is a challenge. Progress in this field depends greatly on the development of high-performance flame retardants. In the work reported here, a unique ladder-like multi-functional polysiloxane (PN-PSQ), with a large number of amine groups and a phosphaphenanthrene structure, was synthesized through the controlled hydrolysis of self-made phosphorus-containing triethoxysilane and gamma-aminopropyl triethoxysilane. A series of PN-PSQ/bismaleimide (BMI) resins was then prepared and their structure and integrated properties investigated. The results show that a small addition of PN-PSQ effectively gives BMI resins an improved curing process, outstanding flame retardant properties, remarkably improved thermal and dimensional stability as well as a decreased dielectric constant and dielectric loss, completely overcoming the critical disadvantages of currently available flame retardants for thermally resistant polymers. For example, for the PN-PSQ5/BMI resin with 5 wt% PN-PSQ, its limited oxygen index and average heat release rate are about, respectively, 1.6 times and 58% of that of BMI resin alone. Compared with BMI resin alone, the glass transition temperature of the PN-PSQ5/BMI resin is increased by about 10 degrees C. The coefficient of thermal expansion of the former in a glassy or rubbery state and the dielectric constant and loss at 1 MHz decrease by about 10-20%. These attractive performances are attributed to the special structure of PN-PSQ/BMI resins induced by the unique nature of PN-PSQ. This investigation provides a new approach to synthesizing multi-functional polysiloxane and related high-performance resins.