Propylene carbonate
A very slow, high-boiling, low-odor solvent used to thin polyurea A-sides and clean equipment, and VOC-exempt under US EPA rules.
Propylene carbonate is a cyclic carbonate ester that boils at about 242 °C. It is a clear, nearly odorless liquid with very low volatility. US EPA exempted it from the VOC definition in 2009.
In polyurea and polyurethane systems it is used as a viscosity reducer or plasticizer in A-sides, and as a low-odor cleaning and flushing solvent for spray equipment. It also appears in some cleaners and paint strippers.
PC contains no reactive hydrogens, so it is compatible with isocyanates. Because it evaporates very slowly, much of it remains in the cured film, where it acts as a plasticizer; formulators limit the amount for that reason.
PC has low acute toxicity but irritates eyes. It is combustible at elevated temperatures. Follow the SDS and use eye protection.
It lowers viscosity for better mixing and atomization without reacting with the isocyanate. Excess amounts can soften the cured film.
It is a common low-odor, low-volatility flushing solvent for plural-component equipment. Follow equipment manufacturer guidance.
