Preparation and characterizations of inherent flame retarded polyamide 66 containing the phosphorus linking pendent group

Polyamide 66 (PA66) containing the phosphorus linking pendent group with inherent flame retardancy property was prepared by condensation polymerization of hexamethylene diammonium adipate (AH salt) and 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-10-phosphaphenanthrene-10-oxide (DDP) as a co-monomer. Prior to condensation polymerization, DDP was reacted with hexamethylene diamine (HMDA), which made DDP easier to react with AH salt. Then, the DDP-HMDA was introduced into AH salt solution to prepare inherent flame retarded PA66 (FRPA66). Fourier transform infrared spectra, nuclear magnetic resonance spectra, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis, tensile test, vertical burning test, limiting oxygen index test, cone calorimetry, and scanning electron microscopy were utilized to investigate the properties of FRPA66. Experimental results indicated that the bulky pendent phosphorus group tended to destroy the structure regularity of FRPA66 and the molecular weight, crystallinity, and thermal stability reduced. The tensile strength of FRPA66 containing 5wt% of DDP was 58.44MPa, and it can achieve a V-0 rating according to the vertical burning test with the limiting oxygen index value of 33.2%. This indicated that the inherent flame retarded PA66 expanded the application of PA66 materials.