Chemistry Reference
In-Depth Information
moieties offer the “side-walk” type defects along the chain. The melting
temperature of the copolymers is decreased while the aromatic character
and the linear contour of the molecules remain. The copolymers of HBA
with HNA should have not only good thermal and mechanical proper-
ties, but also much better processibility than the homopolymer of HBA.
HNA is thus widely used in the molecular engineering of high performance
structural polymers.
2,6-Naphthalene monomers other than HNA, including 2,6-
dihydroxynaphthalene (DHN) and 2,6-naphthadioic acid (NDA), play the
same rule as HNA and are used in many cases. For example, the acetate
of DHN was copolymerized with TA and HBA with a molar ratio of 1:1:2
to give a copolymer which melts at 285
◦
C (Calundann, 1980). When
the molar ratio was changed to 1:1:3 the melting point was found to
be 298
◦
C-305
◦
C. On the other hand, NDA was copolymerized with 1,4-
hydroquinone (HQ) and HBA (Calundann, 1978). The product with 1:1:3
of NDA:HQ:HBA melts at 325
◦
C-340
◦
C. The melting point of the copoly-
mer from a more rigid unit 4
,
4
-dihydroxybiphenyl (HBP) rather than
HQ with the same NDA : HBP : HBA molar ratio of 1:1:3 is also below
400
◦
C (385
◦
C-395
◦
C). However, it is obviously much easier to achieve a
stoichiometric feed of the functional groups when HNA is used than when
a pair of the diol (DHN) and diacid (NDA) monomers is used. High molec-
ular weight polymers should be obtained with less di
culty by using HNA.
In addition, because the substitutions on the naphthalene ring in HNA
are asymmetric, the melting point can be decreased with high e
ciency
by using a small amount of HNA. Thus, the studies in this category have
been mostly on the HBA/HNA copolymers. The HBA/HNA copolymers
have been commercialized as Vectra resins and Vectran fibers by Hoechst
Celanese with success.
Data given in Table 5.7 shows the effect of polymer composition and
heat treatment on the tensile properties of HBA/HNA fibers. The copoly-
mers with approximately a molar ratio of 3/1 of HBA/HNA seem to give
the best balance of properties after heat treatment. The properties of a
representative Vectran fibers are shown in Table 5.8.
As shown in Table 5.7, the heat treatment resulted in the higher ten-
sile properties of the fibers. However, Muramatsu and Krigbaum (1986)
found that the fiber properties were dependent on the spin temperature and
the draw ratio. The heat treatment improved the fiber properties only if
the draw ratio was high. For instance, the initial modulus for HBA/42HNA
(“42” is the mol-% of HNA moieties) fibers spun at 260
◦
Cor280
◦
C
