In this paper 3 parts of research works on fiberformed polyethyleneterephtalate copolyesters are discussed.(1) Effect of chemical structure of comonomers on the propertites of copolyesters.The experimental results indicate the obvios difference in the physical properties between copolymer obtained from comonomer with iso-or ortho-structure of phenyl ring and copolymer obtained from comonomer with flexible chain

For example

in comparison with polyethyleneterephtalate the glass transition temperature of the latter is decreased more than the former;the crystallization rate of the former is decreased

but the crystallization rate of the latter is increased.(2) Effect of physical properties of copolyesters on properties of fibers.For example

decreasing of glass transition temperature of copolyester is advantageous for improving the dyeing propertie of fiber

so the copolyester with flexble chain can be applied to modification of dyeability of fiber because the glass transition temperature of this type of copolyester is abvious lower than that of normal polyester PET .(3) A new type of fiberformed copolyester-normal pressure disperse dye copolyester is discussed.