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Preparation and characterization of poly(ethylene terephthalate) copolyesters and fibers modified with sodium-5-sulfo-bis-(hydroxyethyl)-isophthalate and poly(ethylene glycol)

New copolyesters were successfully prepared with SIPE and PEG units designated as cationic dyeable polyester and easy cationic dyeable polyester. The number average molecular weight of PEG unit is 6000 (abbreviated as PEG6000). Corresponding copolyesters were spun into fibers with melt spinning method. Chemical and crystalline structures were characterized by the NMR and WAXD measurement, and thermal properties were tested by Differential Scanning Calorimetry and Thermogravimetric Analysis, respectively. NMR experimental results indicated the actual molar ratio of comonomers was basically consistent with the correlative feed ratio. WAXD results showed that crystalline structures of prepared copolyesters were similar to that of Poly(ethylene terephthalate). Moreover, the glass transition temperature, melting temperature, and thermal degradation temperature were found to decrease with the increase in weight ratio of PEG6000 units since the incorporation of higher PEG6000 content brought more ether bonds into molecular chains, which increased the asymmetry and irregularity of molecular chains and led to lower crystallinity. Besides, when content of PEG6000 increased, the breaking tenacity and initial modulus were reduced, yet elongation at break enhanced. It suggested that PEG6000 segments reduced the symmetry of molecular chains and decreased the orientation degree of fibers. In addition, because the incorporation of higher weight percentage of PEG6000 led to more hydroxyl end groups and ether bonds in molecular chains, the moisture regain of fibers increased, manifesting fibers had better hydrophilicity with increasing weight ratio of PEG6000 components.