Propoxylation

Propoxylation is a chemical process in which propylene oxide is added to molecules bearing active hydrogen, such as alcohols, phenols, or amines, to form polyether chains with propoxy units. It is a subset of alkoxylation, alongside ethoxylation and butoxylation, and is widely used to prepare polyether polyols and nonionic surfactants.

Propoxylation proceeds by ring opening of propylene oxide, catalyzed by basic, acidic, or ionic catalysts. In anionic (base-initiated) processes, an active initiator deprotonates to form an alkoxide that adds PO units stepwise, yielding poly(propylene glycol) chains with hydroxyl end groups. In cationic processes, PO opens under acid catalysis to form similar polyethers. The PO-to-initiator ratio controls molecular weight; structure can be linear or slightly branched depending on method.

The resulting polyether polyols, particularly polypropylene glycols, are key feedstocks for polyurethane foams and elastomers. Propoxylated alcohols and phenols are also used as nonionic surfactants, detergents, lubricants, and cosmetic ingredients. The hydrophilic-lipophilic balance of products can be tuned by adjusting the propoxylation degree, sometimes combined with ethoxylation or butoxylation to yield block or random copolymers.

Propylene oxide is hazardous and highly reactive; proper handling, ventilation, and controls are required. Residual monomer and catalyst residues must be managed to meet product specifications and environmental regulations.