Sulfur’s Role in the Flame Retardancy of Thio-Ether–linked Hyperbranched Poly(phosphoesters) in Epoxy Resins

•Investigating sulfur’s role in the multifunctionality of hyperbranched poly(phosphoesters).•Two sulfur-containing flame retardants are synthesized: thio-ether and sulfone.•Multi-methodical approach used to understand decomposition pathway.•The incorporation of sulfur changes the modes of action of FRs.•Thio-ethers: S-radical generators; sulfones: flame dilution.