How Hydrogen Bond Interactions Affect the Flame Retardancy and Anti-Dripping Performances of PET

To systematically study how the H-bonding interaction affect the flame retardancy and anti-dripping behavior of poly(ethylene terephthalate) (PET), two series of PET-based copolyesters are prepared by introducing two benzimidazole monomers with similar structure. One (2-(4-methoxycarbonyl-phenyl)-1H-benzimidazole-5-carboxylic acid methyl ester, PBM) contains H-bonding donor, the other (2-(4-methoxycarbonyl-phenyl)-1-methylbenzimidazole-5-carboxylic acid methyl ester, PNM) weeds out the H-bonding donor by replacing -NH group with -N-CH3. The dynamic rheological behavior, fire resistance and fire-retardant mechanism of the PET-co-PBMs and PET-co-PNMs are contrastively investigated. PET-co-PNMs have flow behaviors similar to neat PET. While, for PET-co-PBMs, the movements of the molecular chains are restricted due to the H-bonding interaction, leading to higher melt viscosity, which is conducive to the anti-dripping property. It can be proved that benzimidazole groups promote the carbonization of substrates to form more stable charred layers in combustion, showing an obvious barrier action in condensed phase. Unfortunately, the enhancement of carbonization alone is not enough to inhibit the dripping behavior satisfactorily, and PET-co-PNMs fail to pass UL-94 V-0 rating. While, PET-co-PBMs exhibit better self-extinguishing and anti-dripping performances benefiting from strong H-bonding interactions. The revealed effects of H-bonding interactions on the fire resistance and anti-dripping behavior of polymers will guide further design of flame retardants.