The solvents used are polyethylene glycol 400 and propylene glycol. Other major products are polypropylene glycol, propylene glycol ethers, and propylene carbonate. It is a cyclic carbonate ester derived from propylene glycol. Diethylene glycol is a potential byproduct of propylene glycol. Airlines use deicing fluids based on ethylene glycol or propylene glycol as the active ingredient. Antifreeze products for automotive use containing propylene glycol in place of ethylene glycol are available. Polypropylene glycol is produced by ring-opening polymerization of propylene oxide. The latter include cracking gas, acetylene, ethylene, propylene and butadiene. Fluorinated ethylene propylene (FEP) is a copolymer of hexafluoropropylene and tetrafluoroethylene. PAN is soluble in polar solvents, such as dimethylformamide, dimethylacetamide, ethylene and propylene carbonates. Although many organic carbonates are produced using phosgene, propylene and ethylene carbonates are exceptions. Bulk polymers derived from ethylene and propylene are often prepared via Ziegler-Natta catalysis. E-liquid containing glycerin and water made without propylene glycol are also sold. Acetol can be converted to propylene glycol. The risk from the inhalation of propylene glycol and glycerin is probably low.