Phosphorus containing PET and PEN by direct esterification

A series of various flame retardant copolyesters containing various amounts of phosphorus were synthesized by direct esterification process using the compound of [(6-oxido-6H-dibenz [c,e] [1,2] oxaphosphorin-6-yl)methyl]butan edioic acid (ODOP-BDA) and bis (hydroxyethyl) terephthalate (BHET) or bis ( hydroxyethyl) naphthalate (BHEN). The copolyesters having inherent viscosit y of 0.517-0.617 dl/g were obtained in quantitative yield. These phosphorus -containing copolyesters have good thermal and flame retardant properties. These copolyesters were investigated by the differential scanning calorimet ry (DSC) and thermal gravimetric analysis (TGA). Owing to the incorporation of the rigid structure of DOPO and pendant P group, the resulting phosphor us containing copolyesters exhibited better flame retardancy, higher char y ield and thermal stability than homopolymers of PET and PEN. UL 94-VO ratin g could be achieved with a phosphorus content of as low as 0.75% for PET, 0 .5% for PEN and no fume and toxic gas emission were observed. (C) 1999 Else vier Science Ltd. All rights reserved.