Synthesis of a phosphinated acetoxybenzoic acid and its application in enhancing Tg and flame retardancy of poly(ethylene terephthalate)

A new phosphinated acetoxybenzoic acid, 1‐(4‐acetoxyphenyl)‐1‐(4‐carboxylphenyl)‐1‐(6‐oxido‐6H‐dibenz <1,2> oxaphosphorin‐6‐yl)ethane (3), was prepared by a three‐step procedure. Phosphinated copolyesters based on the acidolysis and polycondensation of (3) with poly(ethylene terephthalate) (PET) were prepared. The crystallinity of copolyesters decreased gradually with the content of (3), as shown in wide‐angle X‐ray diffractograms and differential scanning calorimetry thermograms. Dynamic mechanical analysis and thermal mechanical analysis show Tg increased with the content of (3). UL‐94 flame retardant test shows that the flame resistance of PET was enhanced with the content of (3), and a copolyester with UL‐94 V‐0 grade can be achieved with a phosphorus content as low as 1.43 wt %.