Melting point depression and cocrystallization behavior of poly(ethylene-co-butylene 2,6-naphthalate) copolymers

摘要

The melting point depression and cocrystallization behavior of a series of random poly(ethylene-co-butylene 2,6-naphthalate) P(EN-co-BN) copolymers were investigated using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). These copolymers crystallize over the entire range of composition and they exhibit eutectic behavior. WAXD patterns showed that copolymers form exclusively poly(ethylene 2,6-naphthalate) (PEN) type crystals or poly(butylene 2,6-naphthalate) (PBN) type crystals. A transition from the PEN- to PBN-type crystal was observed in the middle of the copolymer composition. This confirms that the P(EN-co-BN) copolymers show isodimorphic cocrystallization. The cocrystallization was thermodynamically analyzed using the Wendling-Suter model. The defect free energy was found to be about 12.17 kJ mol~(-1) in the case of incorporation of BN units in the PEN-type crystals, and about 5.66 kJ mol~(-1) in the case of incorporation of EN units in the PBN-type crystal. This means that the incorporation of bulkier BN units in the PEN crystals is more difficult. For low comonomer concentrations it was found that comonomer exclusion is probable.