Page 158 - Handbook of Plastics Technologies

THERMOSETS

3.28 CHAPTER 3

TABLE 3.25 Vinyl Ester Formulations
Ingredients Standard Acid-modified Rubber-modified
Epoxy resin 1032 1032 609

Methacrylic acid 195 171 76
Maleic acid 32
CTBN 228
Styrene 970 970
Hydroquinone 0.45 0.45 0.17

TABLE 3.26 Vinyl Ester Properties

Cast Reinforced
Tensile modulus, kpsi 460 1590
Tensile strength, kpsi 11 24
Ultimate elongation, % 6 1
Impact strength, fpi 0.4 28
Heat deflection temperatures, °C 102 260

lecular flexibility, increasing elongation and impact strength, at the expense of modulus,
strength, and heat deflection temperature. Conversely, novolac epoxy gives much higher
cross-linking, increasing modulus, strength, and heat deflection temperature (148°C) at the
expense of elongation and impact strength. Acrylic acid is used instead of methacrylic acid
to produce vinyl esters for UV-cured coatings. Tetrabromobisphenol A builds flame-retar-
dance into the polymer. Use of some maleic acid in place of methacrylic acid builds some
acid groups onto the ends of the vinyl ester molecule; this permits MgO gelation for sheet
molding compound. Use of some carboxy-terminated butadiene-nitrile oligomer (CTBN)
in place of methacrylic acid builds nitrile rubber structure into the polymer, increasing im-
pact strength. And the –OH groups of the epoxy resin can be cross-linked by diisocyanate
to build some polyurethane structure and properties into the cured polymer. A number of
these variations are available commercially.

3.1.3.2.4 Processing. Reinforcement, shaping, and cure of vinyl esters is quite simi-
lar to processes described earlier for polyesters (Sec. 3.1.3.1.3).
3.1.3.3 Allyls. The allyl group CH =CH-CH - is less reactive than conventional vinyl
2
2
monomers CH =CH-X, which offers both advantages and disadvantages. Several allyl
2
monomers have found unique applications in plastics: diallyl phthalate, triallyl cyanurate,
and diethylene glycol bis(allyl carbonate).
3.1.3.3.1 Diallyl phthalate. Glass-fiber-reinforced diallyl phthalate (DAP) is supe-
rior to unsaturated polyesters in shelf life and especially resistance to heat and moisture

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