These polymers have ether functionality in the main chain. They tend to be quite flexible and contribute impact resistance to bulk properties. Many of the polyethers have functional groups at their chain ends and are used to prepare higher molecular weight polymers. Thus, they could also be classified as macromonomers. They are commonly used in the preparation of polyesters and polyurethanes. Poly(propylene glycol) polymers and oligomers (DOWANOL®s) are included in this category. Additional polyethers, including aromatic resins, are found in the Engineering Polymers section.