Glycerol propoxylate (polyether triol)
Glycerol-started polyether triols are the simplest way to add branching to a polyurethane: one extra hydroxyl per molecule turns linear chains into a crosslinked network.
A polyether triol is made by adding propylene oxide (sometimes capped with ethylene oxide) to glycerol, which supplies three hydroxyl starting points. The result is a three-armed polypropylene glycol with an OH group at the end of each arm. Commercial grades range from low molecular weight (a few hundred g/mol) to around 6,000 g/mol.
On the B-side of polyurethane coatings, elastomers, sealants and foams, triols build crosslink density. Low-molecular-weight triols give hard, chemically resistant networks; high-molecular-weight triols add flexibility while still crosslinking. Formulators often blend triols with diols to tune hardness, elongation and solvent resistance. Polyurea systems use the amine-terminated analogue (polyetheramine triols) instead.
The key numbers are functionality (3) and OH number, which together give the equivalent weight:
Polyether triols have low volatility and low acute toxicity, and many grades are not classified as hazardous; check the SDS for the specific product. Keep containers closed and dry (nitrogen padding is common), because absorbed water causes foaming and pinholes in polyurethane films. Warm viscous grades gently before pumping.
Divide 56,100 by the OH number (mg KOH/g). A triol with an OH number of 56 has an equivalent weight of about 1,000 g/eq.
It increases crosslink density, which typically raises hardness, chemical and solvent resistance and Tg, while reducing elongation. High-molecular-weight triols crosslink with less loss of flexibility.
Water reacts with isocyanate to form an amine and carbon dioxide gas. Even a few tenths of a percent of water in a polyol can cause foaming, pinholes and soft spots.
Polyurea B-sides use amine-terminated polyethers, including triamines, rather than hydroxyl-terminated triols, because amines react with isocyanate far faster.
