Polypropylene glycol

Lore & Background

Polypropylene glycol is produced by ring-opening polymerization of propylene oxide, initiated by an alcohol and catalyzed by a base, usually potassium hydroxide. When the initiator is ethylene glycol or water, the polymer is linear; with multifunctional initiators like glycerine, pentaerythritol, or sorbitol, it branches. Conventional polymerization yields an atactic polymer, while isotactic polymer can be produced from optically active propylene oxide at high cost.

Reader's Guide

Polypropylene glycol is significant for its use in many polyurethane formulations and in the synthesis of waterborne polymers. Its backbone, with three carbons per oxygen from propylene oxide, confers some water miscibility, though less than ethylene oxide-based molecules. It is used to synthesize the epoxy reactive diluent and flexibilizer poly(propylene glycol) diglycidyl ether. PPG also serves as a surfactant, wetting agent, and dispersant in leather finishing, as a reference and calibrant in mass spectrometry and HPLC, and as a defoamer in drilling. It is a primary ingredient in paintballs and has been evaluated as a corrosion inhibitor. Its lower toxicity compared to polyethylene glycol has led to its use in biotechnologicals.

Did You Know?

• Between 60 and 70% of propylene oxide is converted to polyether polyols by alkoxylation.
• Secondary hydroxyl groups in PPG are less reactive than primary hydroxyl groups in polyethylene glycol.
• PPG is less toxic than PEG, so biotechnologicals are now mainly produced with PPG.