256 HIGH PERFORMANCE POLYMERS
that converts the cyclic oligomers to high-molecular-
weight linear polymers by ring-opening polymeriza-
tion methods.
11.2.1 Poly(ethylene naphthalate)
PEN was first described in 1948 [4]. Commercially,
PEN is prepared by a two-step reaction consisting
of [7]:
1. Esterification between 2,6-naphthalene dicar-
boxylic acid and glycol to obtain a low-
molecular-weight esterified compound, and
2. Polycondensation reaction of the esterified
compound to obtain a higher molecular weight
PEN product.
Either NDC or the acid itself can be used. Using
the dimethyl ester, zinc acetate or manganese acetate
as a catalyst a t a reaction temperature of 180–260
◦
C
is needed to produce (β-hydroxyethyl) naphthalate, or
its low-molecular-weight prepolymer ...