The crystallization kinetics of poly(butylene 2,6-naphthalate) and its copolyesters has been investigated by differential scanning calorimetry at large undercoolings. Wide angle X-ray diffraction patterns show that the copolymers crystallize purely in crystalline phase of poly(butylene 2,6-naphthalate). In contrast to the typical crystallization behavior of copolymer, the crystallization isotherms follow the Avrami equation up to high degree of conversion, and the Avrami exponents are mostly close to 2, independent of copolymer composition and crystallization temperature. The analysis of kinetic data with a modified Lauritzen-Hoffman equation indicates that the product of the lateral surface free energy and the fold one (sigma sigma(c)) is 1410 +/- 100 erg(2) cm(-4) and this value is not dependent on copolymer composition. The surface free energies and the work of chain folding are also discussed in comparison with those of poly(butylene terephthalate) and poly(ethylene terephthalate).
