A Creative Approach to Prepare a Macromolecular Flame Retardant with Flexibility: DOPO-Modified Epoxidized Polybutadiene

The incorporation of large loading of flame retardants generally causes embrittlement of materials. However, most of the rubbers and thermoplastic elastomers are flammable. Therefore, preparation of a flame retardant with potential toughening characteristics is urgently required for preparing materials with both good flame retardancy and toughness. The objective of the present work was to prepare a macromolecular flame retardant with good flexibility, that is, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-modified epoxidized polybutadiene (EPB–DOPO) via a creative approach of two-step reactions. First, polybutadiene (PB) was partially epoxidized to generate EPB; second, the reactive flame retardant DOPO reacted with epoxy groups to generate EPB–DOPO. EPB–DOPO with three epoxidation degrees was prepared: EPB5%–DOPO, EPB10%–DOPO, and EPB15%–DOPO. The chemical structure of EPB–DOPO was confirmed with proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectra. Thermogravimetric analysis (TGA) showed that EPB–DOPO had good thermal stability. EPB10%–DOPO and EPB15%–DOPO passed the UL-94 V-2 and V-0 rating, respectively, and the gas-phase flame retardation mechanism was deduced. The glass transition temperature (Tg) of EPB–DOPO prepared in this study was below −20 °C. Due to little char formation, EPB10%–DOPO and EPB15%–DOPO showed good resilience even after flame ignition. This study has provided a creative strategy to prepare a macromolecular flame retardant with good flexibility.