Synthesis, flame‐retardancy testing, and preliminary mechanism studies of nonhalogenated aromatic boronic acids: A new class of condensed‐phase polymer flame‐retardant additives for acrylonitrile–butadiene–styrene and polycarbonate

This study describes the syntheses and thermal properties of aromatic boronic acids and their use as flame retardants. The possible flame-retardancy mechanisms are also discussed. The materials were synthesized from aromatic bromides using one of two procedures. The first procedure involved traditional approaches to boronic acids, using lithium–halogen exchange and quenching with trimethylborate followed by hydrolysis. The second procedure used a nickel catalyst and a dialkoxy borane to generate aromatic dialkoxyboronates that were converted to boronic acids by acid hydrolysis. The thermal properties of these aromatic boronic acids were studied using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). These materials were blended into acrylonitrile–butadiene–styrene (ABS) and polycarbonate (PC) resins and tested for ignition resistance, using the UL-94 flame test. A 10 wt % loading of 1,4-benzenediboronic acid in polycarbonate gave a UL-94 V-0 result. This same diboronic acid showed flame retardancy and char formation in ABS, but this result was not quantifiable by the UL-94 test. Burn times for the ABS samples often exceeded 5 min, thereby showing unusual resistance to consumption by fire.