Noryl is a blend of polyphenylene oxide (PPO) and polystyrene
(PS) which was developed in 1966 by General Electric Plastics
(now owned by SABIC). It is a rare example of a homogeneous
mixture of two polymers. Most polymers are incompatible with one
another, so tend to produce separate phases when mixed. The
compatibility of the two polymers in Noryl is caused by the
presence of a benzene ring in the repeat units of both chains.
The addition of polystyrene to PPO increases the glass
transition temperature above 100 °C, owing to the high Tg of
PPO, so Noryl is stable in boiling water. The precise value of
the transition depends on the exact composition of the grade
being used. There is a smooth linear relation between weight
content of polystyrene and the Tg of the blend. Noryl has good
electrical resistance, so is widely used for switch boxes.
However, product design is important in maximising the strength
of the product, especially in eliminating sharp corners and
other stress concentrations. Injection moldin