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Encyclopedia of Physical Science and Technology En012c-604 July 26, 2001 16:2

780 Polymers, Thermally Stable

TABLE I Comparison of Properties of Xylylene Polymers with Epoxy and Silicone Materials a
Polymonochloro- Polydichloro-
Poly-p-xylylene p-xylylene p-xylylene
Property (Parylene N) (Parylene C) (Parylene D) Epoxy Silicon
Density 1.11 1.289 1.418 1.11–1.40 1.05–1.23
Tensile strength (MPa) 45 69 76 28–90 6–7
Elongation at break (%) 30 200 10 3–6 100
24-hr water absorption (%) 0.06 0.01 — 0.08–0.15 0.12 (7 days)
◦
Melting or heat distortion temperature ( C) 405 280 >350 Up to 220 Up to 300
/ C)
Linear coefficient of expansion (10 −5 ◦ 3.5 6.9 — 4.5–6.5 25–30
Dielectric strength (V/mil) 7000 5600 5500 2300 2000
◦
Volume resistivity 23 C 50% RH ( -cm) 1 × 10 17 6 × 10 16 2 × 10 16 1 × 10 14 1 × 10 15
◦
Surface resistivity 23 C 50% RH ( -cm) 10 13 10 14 5 × 10 16 5 × 10 3 3 × 10 13
Dielectric constant
60 Hz 2.65 3.15 2.84 4.2 2.6
3
10 Hz 2.65 3.10 2.82 3.9 2.6
6
10 Hz 2.65 2.95 2.80 3.4 2.6
Dissipation factor
60 Hz 0.0002 0.020 0.004 0.03 0.0005
3
10 Hz 0.0002 0.019 0.003 0.03 0.0004
6
10 Hz 0.0006 lhl0.013 0.002 0.04 0.0008
a
Reprinted with permission from Critchley, J. P., Knight, G. J., and Wright, W. W. (1983). “Heat Resistant Polymers—Technologically
Useful Materials,” Plenum, New York. Copyright 1983 Plenum Press.

the polymers are characterized by a combined low solubil- aramid system in order to obtain the maximum thermal
ity and high melt temperature, most prominent in wholly stability benefits from high polymer melt temperatures
para- and least in wholly meta-oriented systems. Vari- while increasing the most important feature in the spin-
ous approaches have been applied toward “tailoring” the ning of high-quality fiber, that is solubility. Typically, the

FIGURE 2 Thermal stability envelopes for poly-p-xylylenes in inert and oxidizing atmospheres. (A) From Wurtz
reaction and (B) from pyrolysis of p-xylene. [Reprinted with permission from Critchley, J. P., Knight, G. J., and Wright,
W. W. (1983). “Heat Resistant Polymers—Technologically Useful Materials,” Plenum, New York. Copyright 1983
Plenum Press.]