
11: POLY(NAPHTHALATES) 265
2,6-NDA have been proposed. These suffer from
insufficient gas barrier properties and generate
acetaldehyde.
A polyester composition having better gas barrier
properties with less acetaldehyde ejection consists of
a blend of prepolymers of PET and PEN, or a copoly-
mer. This blend is subjected to the solid state polymer-
ization process [57].
The PEN copolymer is prepared from 2,6-dimethyl
naphthalate, dimethyl isophthalate, ethylene glycol,
and poly(tetramethylene glycol), with an average
molecular weight of 1000 Da.
A dry blend of 90% of a prepolymer of the PET,
and 10% of the prepolymer of the PEN is then melt
kneaded at a molding ...