Preparation of modified polyesters containing triphosphorous and their applications to PU flame-retardant coatings

Three phosphorous functional groups were introduced in one structural unit of polymer backbone to enhance the flame retardancy of PU coatings. In the first step, we synthesized tetramethylene bis(orthophosphate) (TBOP) that contained two phosphorus functional groups in one structural unit. In the next step, we synthesized modified polyesters (ATBTP-10,-20,-30) that contained triphosphorous groups by condensing polymerization of TBOP, 1,4-butanediol, trimethylolpropane, adipic acid, and phenylphosphonic acid (PPA). The amount of PPA in the ATBTPs was 10, 20, and 30 wt%. Then, flame-retardant PU coatings (AHFC−10,−20,−30) were prepared by curing ATBTPs with hexamethylene diisocyanate-biuret (curing agent) at room temperature. From the TGA analysis of diphosphorus-modified polyester (ATBT) and ATBTPs, the residues of ATBT, ATBTP-10, ATBTP-20, and ATBTP-30 were 24.6, 27.5, 29.2, and 31.9%, respectively. From this result, it was found that the residue increased in relation to the amount of PPA. Physical properties of the films of flame-retardant coatings were deteriorated with the addition of PPA (flame retarding component), however, all the films of flame-retardant coatings, except AHFC-30, met the required physical properties standard for coatings. Char lengths of the AHFCs measured by the 45° Meckel burner method were 2.9∼4.8 cm, and LOI values were 28∼31%, which indicates that the prepared AHFCs showed good flame retardancy.