Fine structures of copolyesters containing naphthalene and phenanthrene rings

Abstract

Copolyesters composed of poly(ethylene-2,6-naphthalate) and poly(ethylene-2,7-phenanthrate) (PEN/PEP copolymers) with different copolymer compositions were synthesized. The thermal properties and fine structures of the isotropic and oriented samples were investigated using thermal analysis and X-ray diffraction methods. The glass transition temperatures ( T g) of the copolymers increased with increasing molar fraction of the PEP component. The undrawn annealed samples containing 5% PEP (NP5) exhibited X-ray diffraction patterns showing the coexistence of the α and β-polymorphic forms of PEN. In samples containing 10 and 20% PEP (NP10 and NP20), the crystallites were of the β-form of PEN. On the other hand, drawn NP5 and NP10 exhibited the α-form. The WAXD pattern of the drawn NP20 was different from those of the above two samples, and could not be assigned to either the α or the β-form. PEP sequences interfere with the crystallization and have a strong influence on the chain packing mode of the unit cell in the copolymers.