Structure–property relationship in copolyesters. I. Preparation and characterization of ethylene terephthalate–hexamethylene terephthalate copolymers

Poly(ethylene terephthalate)-containing ethylene and hexamethylene residues in the polymer backbone were prepared by melt condensation reaction of dimethyl terephthalate (DMT) and diffrent quantities of ethylene glycol (EG) and 1,6-hexane diol (H) in the initial monomer feed. Several polyester samples were prepared by varying the mol % of 1,6-hexane diol with respect to ethylene glycol in the initial monomer feed. These included 0.0 (PET), 2.5 (H₁), 5.0 (H₂), 7.5 (H₃), 10.0 (H₄), 12.5 (H₅), 15.0 (H₆), 17.5 (H₇), 20.0 (H₈), 50.0 (H₉), 80.0 (H₁₀), and 100.0 (H₁₁), respectively. The polymers were characterized by recording IR spectra and intrinsic viscosity measurements. The relative thermal stability of the polymers was evaluated by dynamic thermogravimetry in air. An increase in mol % of 1,6-hexane diol resulted in a decrease in melting points and thermal stability of copolymers. PET and copolyesters were spun to fibers by using the melt-spinning technique. The fibers were drawn to draw ratios 2,3,4, and 5. In case of copolymes, tensile strength decreases slightly with increasing mol % of H whereas % elongation increases. The moisture regain and dye uptake in copolyesters was treatly enhanced as compared to PET.