Flame‐retardant ABS resins from novel phenyl isocyanate blocked novolac phenols and triphenyl phosphate

In an effort to prepare a novel novolac phenol (NP) based char former with good solubility, the hydroxyl functionalities of NP were blocked with phenyl isocyanate (PI) via a simple urethane‐forming reaction. The chemical structure and properties of the obtained novolac phenol–phenyl isocyanate adduct (NP–PI) were characterized with gel permeation chromatography, Fourier transform infrared spectroscopy, 1H‐NMR, and differential scanning calorimetry. Adducts of two kinds of NPs (molecular weights = 450 and 800) with PI were used as potential char formers for this study. Thus, a two‐component system using NP–PI as a char former and triphenyl phosphate (TPP) as a phosphorous‐based flame retardant was blended with ABS, and the thermal degradation behavior and flame retardance were examined as a function of the molar mass of NP–PI and the TPP/NP–PI ratio with thermogravimetric analysis and limiting oxygen index (LOI) testing. ABS compositions with no NP–PI were also prepared for comparison. The mixtures showed a synergistic effect between TPP and NP–PI on the flame‐retardance enhancement of ABS. Those containing the higher molar mass NP–PI adduct were the most flame retardant, and a LOI value as high as 41 was obtained.