Polyphenylene oxide (PPO) – also known as polyphenylene ether (PPE) – is an amorphous thermoplastic consisting of aromatic phenylene rings linked together via ether bonds. While PPO by itself is unsuitable for injection molding, it is easily blended with other materials (including polystyrene, ABS, nylon, thermoplastic polyester) to improve processing, reduce cost, and target specific performance requirements.

General Electric Plastics first introduced a modified resin in the early 1960’s under the trade name Noryl®. Noryl® was a blend of PPO and polystyrene, and the properties and characteristics of each grade were dependent on the ratio of the blend. Unlike a number of other commercial polymers – which were alloys of different polymers (or co-polymers) – Noryl® was a true blend, where the materials were simply mixed together, with no chemical bonding between the base polymers. (The blending capability of PPO is an important characteristic to remember, IMHO).

Polyphenylene resins have an excellent blend of physical properties, along with excellent electrical properties. PPO has an exceptionally high glass transition temperature. As a result, parts made of this material have a very high useful temperature range. Some grades are often used in medical applications for parts and components that must undergo sterilization (via steam, gamma radiation, or ethylene oxide)

PPO blends are used for structural parts, electronics, household appliances, and automotive components.

Taken as a class, modified PPO is one of the Big 5 engineering plastics (along with nylon, polycarbonate, acetal, and thermoplastic polyester). It is an important engineering material, and should be on every design engineer’s palette of materials.