60 SPECIALTY POLYMERS
Table 3.9 Properties of polyetheretherketone
30% glass
fibre
Property Unfilled filled
Tensile strength (MPa) 92 157
Elongation at break (%) 4.9 2.2
(yield)
Flexural modulus (GPa) 3.7 10.3
Notched Izod impact
strength (ASTM, D256) (J m - 1) 83 96
Heat distortion
temperature Cc) 140 315
Limiting oxygen index (%) 35
with polyimides which are sensitive to hydrolysis. Flammability behaviour
is also good with a limiting oxygen index of 40 and very low smoke and
toxic gas production, characteristic of many wholly aromatic polymers.
Applications include electrical products such as high temperature connectors,
film wrapping for cables, wire and cable insulation for fire resistant uses such
as warships and oil wells, hot water pumps, valves and engine components.
Composite prepregs with carbon fibres have been developed for structural
aircraft components. Other types of polymer, so-called polyetherketones,
presumably with fewer flexibilizing ether links, are also under development
(Victrex PEK™, Ultrapek™, and Hostatec™). These polymers have even
higher Tg values and heat distortion temperatures (up to 340°C for glass filled
grades). Typical properties for PEEK are shown in Table 3.9.
3.7 Heterocyclic polymers
Heterocyclic structures in the polymer chain provide another type of ring
structure to stiffen the chain and raise Tg , Tm and softening point. In the
earlier days of the search for high temperature resistant polymers, many such
polymers were synthesized and their thermal degradation behaviour was
investigated. However, hardly any of these materials were ever commercialized
and, despite the much greater variety of thermally stable heterocyclic polymers
potentially available, very few have had any commercial success. By far the
most important of these materials are the polyimides, which were developed
comparatively early, and have been the only real commercial success. The
polybenzimidazoles, also developed in the early 196Os, have only ever achieved
a semi-commercial status. Discussion is largely restricted to these two groups
of materials.
3.7.1 Polyimides
Dupont offered the first commercial polyimide in the early 1960s, made by
condensation between pyromellitic dianhydride and 4,4-diamino diphenyl
Table 3.9 Properties of polyetheretherketone
30% glass
fibre
Property Unfilled filled
Tensile strength (MPa) 92 157
Elongation at break (%) 4.9 2.2
(yield)
Flexural modulus (GPa) 3.7 10.3
Notched Izod impact
strength (ASTM, D256) (J m - 1) 83 96
Heat distortion
temperature Cc) 140 315
Limiting oxygen index (%) 35
with polyimides which are sensitive to hydrolysis. Flammability behaviour
is also good with a limiting oxygen index of 40 and very low smoke and
toxic gas production, characteristic of many wholly aromatic polymers.
Applications include electrical products such as high temperature connectors,
film wrapping for cables, wire and cable insulation for fire resistant uses such
as warships and oil wells, hot water pumps, valves and engine components.
Composite prepregs with carbon fibres have been developed for structural
aircraft components. Other types of polymer, so-called polyetherketones,
presumably with fewer flexibilizing ether links, are also under development
(Victrex PEK™, Ultrapek™, and Hostatec™). These polymers have even
higher Tg values and heat distortion temperatures (up to 340°C for glass filled
grades). Typical properties for PEEK are shown in Table 3.9.
3.7 Heterocyclic polymers
Heterocyclic structures in the polymer chain provide another type of ring
structure to stiffen the chain and raise Tg , Tm and softening point. In the
earlier days of the search for high temperature resistant polymers, many such
polymers were synthesized and their thermal degradation behaviour was
investigated. However, hardly any of these materials were ever commercialized
and, despite the much greater variety of thermally stable heterocyclic polymers
potentially available, very few have had any commercial success. By far the
most important of these materials are the polyimides, which were developed
comparatively early, and have been the only real commercial success. The
polybenzimidazoles, also developed in the early 196Os, have only ever achieved
a semi-commercial status. Discussion is largely restricted to these two groups
of materials.
3.7.1 Polyimides
Dupont offered the first commercial polyimide in the early 1960s, made by
condensation between pyromellitic dianhydride and 4,4-diamino diphenyl
