Page 159 - Handbook of Plastics Technologies

THERMOSETS

THERMOSETS 3.29

aging, leading to electrical and electronic insulation applications such as connectors for
communications equipment, computers, aerospace, potentiometers, circuit boards, potting
vessels, trim pots, coil forms, switches, and TV.
The liquid monomer (Fig. 3.17) is stable at
room temperature, even when “catalyzed” by
peroxides. Conversely, it requires high-temper-
ature peroxides, such as t-butyl perbenzoate
and dicumyl peroxide, higher temperatures
(135 to 177°C), and longer times (0.5 to 4.0
min) to polymerize and cure. It is prepolymer-
ized to solid oligomers and compounded with
FIGURE 3.17 Diallyl phthalate.
fillers and reinforcements to make molding
powders. Cured moldings are best with glass fi-
ber reinforcement (Table 3.27), and long glass fibers give superior strength and impact
strength. They are superior to unsaturated polyester primarily in shelf life and resistance to
hydrolysis and heat aging. Their limitations are cost of monomer and slow cure reactions.

TABLE 3.27 Diallyl Phthalate Molded Properties
Glass fiber reinforcement Short Long

Mold shrinkage, % 0.3 0.2
Flexural modulus, kpsi 1200 1300
Flexural strength, kpsi 12 16
Tensile strength, kpsi 7 10
Compressive strength, kpsi 25 25
Notched Izod impact strength, fpi 0.6 6.0
o
Heat deflection temperature, C 204 200
o
Continuous heat resistance, C 191 191
Dielectric constant 4.4 4.2
Dissipation factor 0.007 0.006
Water absorption, % 0.2 0.25

In addition to the conventional diallyl ortho-phthalate, diallyl iso-phthalate (DIAP) is
also available commercially. It is more expensive but offers higher heat deflection temper-
ature and heat aging resistance (Table 3.28).
Another use of diallyl phthalate monomer is the replacement of styrene monomer in
unsaturated polyesters. DAP is superior to styrene in lower volatility and longer shelf life
but is limited by higher cost and slower cure.

3.1.3.3.2 Triallyl cyanurate. The triazine ring (Fig. 3.18) is stabilized by heterocy-
clic resonance, giving it high heat resistance. This monomer can be used in place of sty-
rene in unsaturated polyesters. It is less volatile than styrene. Being less reactive, it gives

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