Copolyesters based upon ethylene glycol (EG)

terephthalic acid (TPA) and 2

6-naphthalenedicarhoxylic acid(NPA) or isophthalie acid(IPA) of different composition were synthesized by transesterification polycondensation of monomers or polymers．With the involvement of IPA or NPA moieties in the chains

the copolyesters became less crystallizable or amorphous

and the isothermal crystal growth rate decreased rapidly．Tlhe H1-NMR studies of the copolyesters NPA／TPA／EG showed that the samples prepared by different method exhibited a similar random sequence distribution．DSC measurements indicated that the copolyesters NPA/TPA／EG or IPA／TPA／EG are amorphous if the contents of moieties NPA of IPA are higher or equal to 20 mol％．The WAXD of the copolyester sample containing 20 mol％ NPA moieties

after an anneal at 140℃ for 2 hours

exhibited some weak diffraction peak．which is attributed to the crystals of PET moiety in the eopolyester．Due to the introduction of IPA or NPA moieties

the melting temperatures and the cooling crystallization temperatures of the copolyesters were changed．