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High Temperature Windshield-Canopy Materials Development

This report covers the first year of work on the program to develop new. high
temperature stable. transparent plastics for use in high perfomance aircraft
as materials of construction for uindshields and/or canopies. Thirty novel
materials were prepared during this period. each with a glass transition teak
perature exceeding those of currently used acrylic and polycarbonate plastics.
and possessing varying degrees of transparency. color. and impact strength.
and polyesters has resulted in the more thermally stable materials. Depending
upon the reactants involved, new polyesters, polycarbonates. polyester carbonates
copolyesters and copolyester carbonates have been prepared. Materials based
upon tetramethyl dicumyl bis henol (posed AF-gP-Z) havg lass transition tem-
peratures (Tg) ranging from 90 to 228 C (374 F to 442 F ; light transmittance
is generally over 80%; however, haze is rather high, the yellowness index is
high, and the impact strength (notched izod) is between 1.0 to 3.0 ft-lb per
inch of notch. Materials based upon combinations of tetramethyl dicumyl his»
phenol, bisphenol-A, tetraphthoyl chloride and phosgene also possess desirable
properties. Properties of many of the materials have been determined while
others are still in progress.
During the last decade there has been an increasing need
for improved materials of construction for advanced aircraft that
operate at supersonic speeds. One materials area in which con-
siderable deficiencies continue to exist is the transparencies of
windshield - canopy assemblies. Several requirements for these
transparencies are thermal stability, resistance to bird impe t,
abrasion resistance and optical clarity. While glass transparen-
cies have adequate thermal resistance properties, various defi-
ciencies such as the weight of the finished part, brittleness and
fabrication problems are apparent. In addition, glass structures
generally do not have sufficient impact resistance to withstand
damage from bird strikes.
Over the years polymer science and technology has provided
the means of overcoming many of the deficiences of glass
transparencies. Such properties as low density, impact strength
and optical clarity have been relatively easily achieved with
several synthetic plastics. However, the existing plastics which
meet requirements of transparency and impact strength do not
have sufficient heat resistance for windshield - canopy applica-
tions in advanced aircraft. Two noteworthy examples are acrylics
and bisphenci-A polycarbonate. In the case of acrylics the ser-
vice limit is about 250’? (121°C). With polycarbonate 6imen-