Yg. Jeong et al., Cocrystallization behavior of poly(butylene terephthalate-co-butylene 2,6-naphthalate) random copolymers, MACROMOLEC, 33(26), 2000, pp. 9705-9711
A series of poly(butylene terephthalate-co-butylene 2,6-naphthalate) (P(BT-
co-BN)) random copolymers were synthesized, and their cocrystallization beh
avior was investigated by differential scanning calorimetry (DSC) and wide-
angle X-ray diffraction (WAXD). The P(BT-co-BN) copolymers, which are found
to be statistical random copolymers, show a single melting and a single cr
ystallization peak over the entire range of copolymer composition and have
a eutectic melting point in the plot of melting point versus composition. W
AXD patterns of copolymers are divided into two groups, i.e., the PET type
crystal and the PEN type crystal. These facts indicate that the P(BT-co-BN)
copolymers show isodimorphic cocrystallization. The eutectic composition a
t which the crystal transition between PET and PEN type crystal occurs was
estimated ca. 35 mol % BN content. When the defect free energy was calculat
ed by using the equilibrium inclusion model, the defect free energy (6.10 k
J/mol) in the case of incorporation of BN units in the PET type crystal was
higher than the opposite case (3.63 kJ/mol). It means that the incorporati
on of bulkier BN units in the PET type crystal is more sterically hindered
than the opposite case. The changes of heat of fusion and d spacings with c
omposition also support isodimorphic crystallization.