Study of non-isothermal crystallization kinetics and sequence distribution in poly(ethylene terephthalate-co-isophthalate)

The non-isothermal crystallization kinetics of poly(ethylene terephthalate-co-isophthalate) (PEIT) with different isophthalate contents (4, 8 and 12%) were studied by differential scanning calorimetry. Avrami exponent n was obtained. It was found that the n values of PEIT4 and PEIT8 are same as that of poly(ethylene terephthalate) (PET). The n value of PEIT12 is larger than that of PET. PEIT crystallization mechanism appears different with varied isophthalate composition. The sequence distribution in macromolecular chain of PEIT was also investigated by 1H-NMR method. It revealed that PEIT4 and PEIT8 are block-copolymers with isophthalate sequence length >5, and PEIT12 is a random copolymer in which most isophthalate sequence length is 2 or 1. The relationship between the crystallization mechanism and sequence distribution characteristic of PEIT has been discussed.