Preparation and characterization of amorphous poly(ethylene terephthalate)

Copolyesters based upon ethylene glycol (EG), terephthalic acid (TPA) and 2, 6-naphthalenedicarboxylic acid(NPA) or isophthalic 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. The H-1-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 degreesC for 2 hours, exhibited some weak diffraction peak, which is attributed to the crystals of PET moiety in the copolyester. Due to the introduction of IPA or NPA moieties, the melting temperatures and the cooling crystallization temperatures of the copolyesters were changed.