Isomorphic crystallization of aliphatic copolyesters derived from 1,6-hexanediol: Effect of the chemical structure of comonomer units on the extent of cocrystallization

The crystallization behavior has been investigated for poly(hexamethylene sebacate-co-hexamethylene suberate)s [P(HSe-co-HSu)] and poly(hexamethylene suberate-co-hexamethylene adipate)s [P(HSu-co-HA)] copolyesters by differential scanning calorimeter (DSC), wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR) spectrometer. Cocrystallization of comonomer units was found in the crystalline phase of both P(HSe-co-HSu) and P(HSu-co-HA) copolymers. Moreover, both P(HSe-co-HSu) and P(HSu-co-HA) copolymers exhibit isodimorphism. The PHSe and the PHSu type crystals were respectively developed in P(HSe-co-HSu)s, while the PHSu and the PHA type crystals were developed in P(HSu-co-HA)s respectively. The inclusion of the comonomer units in the PHSu type crystalline lattice is more favored than that in the PHSe type crystal of the P(HSe-co-HSu)s. Meanwhile, it is easier for the comonomer units to be incorporated into the PHA type crystalline lattice than into the PHSu type crystal of P(HSu-co-HA)s. Moreover, comparison between the isomorphic crystallization of P(HSe-co-HSu), P(HSe-co-HA) and P(HSu-co-HA) series copolyesters indicates that minimization of the difference in chemical structure helps in increasing the extent of cocrystallization of comonomer units.