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Encyclopedia of Physical Science and Technology en012f-594 July 26, 2001 11:9

670 Polymers, Ferroelectric

[ HN(CH 2 ) x NHOC(CH 2 ) y CO ] are termed odd–odd
nylons if the numbers of carbon atoms in the repeating
units (x and y) are both odd numbers. Nylons are
prepared by melt polymerization solution and interfa-
cial polymerization, ring-opening polymerization, and
anionic polymerization. The morphology and degree of
crystallinity of the nylons depend on the basic structure of
their chemical linkages. Strong interactions between the
amide group of neighboring chains account for the unique
physical properties of nylons, such as toughness, stiffness,
high melting points, and low coefficients of friction.
Odd nylons and odd–odd nylons are important classes
of ferroelectric polymers. Nylons crystallize in all-trans
conformation and are packed so as to maximize the hy-
drogen bonds between the adjacent amine and carbonyl
groups, as seen in Fig. 10. The dipoles of odd nylons
are aligned in the same direction and give rise to a large
dipole moment and spontaneous polarization in the unit
cell of the crystalline phase, whereas the dipole compo-
FIGURE 9 Electric field-induced strain of three VDF/TrFE/CTFE
samples 9–11. nents of even nylons cancel each other out. The density
of NH···C O dipoles per unit volume of nylon is larger
for lower-numbered nylons; thus nylon-5 is expected to
respectively. At ambient temperature, the longitudinal
possess a larger dipole moment (i.e., remnant polariza-
strain was about 4.5% for samples 10 under an electric tion) than nylon-7, nylon-9, and nylon-11. Indeed, the
field of 130 MV/m. A nearly straight line of S versus P 2
experimental results show that the remnant polarization
for sample 10 indicates the electrostrictive response in the
VDF/TrFE/CTFE terpolymer. Based on the electrostric-
2
tive relationship S = QP , this yields an electrostrictive
2
4
coefficient Q of about −5.57 m /C .
IV. OTHER FERROELECTRIC POLYMERS

A. Ferroelectric Nylon

1. Polymeric and Crystal Structure
The discoveries of piezoelectric and pyroelectric proper-
ties in PVDF polymer led to the search for other classes
of novel ferroelectric polymeric materials. Recently, odd-
numbered nylons have emerged as a new class of ferro-
electric polymer similar to PVDF. These materials have
attracted much interest in the past two decades because of
the stability of their electroactive properties at relatively
high temperatures and relatively high electromechanical
coupling coefficient.
Polyamides, commonly known as nylons, have molec-
ular repeated units of ( HN(CH 2 ) x CO ). Generally,
nylons are named after the number of carbon in the
repeating unit of the polymer backbone. For example if
x = 5, the corresponding nylon is identified as nylon-5.
Nylons with an odd number of carbon atoms are called
“odd nylons” and nylons with an even number of
carbon atoms are called “even nylons.” Other categories FIGURE 10 All-trans conformation of odd-numbered and even-
of polyamides having molecular repeating units of numbered nylons. Arrows indicate the dipole direction.