Abstract: | Poly(ethylene terephthalate) was modified by incorporating bis(hydroxyethyl) tetrasubstituted terephthalates (methyl, chlorine, and bromine) as a third component in the mole ratios of 2–50% (based on dimethyl terephthalate) which resulted in random copolyesters. The presence of steric hindrance imparted additional chain rigidity to the copolymer structure, as shown by increased glass transition temperature (Tg). The effectiveness of the steric groups for conferring rigidity to the copolymer structure was CH3 > Cl?Br. The copolyesters which contained halogen substituents showed substantial enhancement in flame retardency compared with PET. |