In situ synthesis of a novel transparent poly (methyl methacrylate) resin with markedly enhanced flame retardancy

A novel phosphorus-containing monomer, (6-oxido-6H-dibenzo[c,e][1,2]oxaphosphinin-6-yl)methyl acrylate (DOPO-AA), is first synthesized and characterized by Fourier transform infrared spectra (FTIR),1H nuclear magnetic resonance (NMR) and31P NMR. The monomer is then introduced into poly (methyl methacrylate) (PMMA) matrix via in situ copolymerization to produce a new PMMA based copolymer (PMMA/DOPO-AA). From UV-vis spectra, microscale combustion calorimeter (MCC) and thermogravimetric analyses (TGA) results, the as-fabricated PMMA/DOPO-AA copolymers not only keep relatively high transparency, but also exhibit remarkable improvements in the flame retardancy and thermal stability, such as increased T0.5by 60.2°C and limited oxygen index (LOI) by 4.1, and decreased peak heat released rate (PHRR) by 34.7%. Thermal degradation behaviors investigated by real time Fourier transform infrared spectra (RTIR), char structure analysis studied by scanning electron microscope (SEM) and pyrolysis gaseous products studied by TGA coupled with FTIR (TGA-FTIR) demonstrate that the catalytic charring function of DOPO-AA in condensed phase and DOPO flame retardant systems in the gas phase are two key factors for the property enhancements. This work not only provides a promising flame-retardant monomer for polymers, but also will stimulate more efforts on the development of DOPO-containing flame-retardant monomers.