Polyethylene glycol, abbreviated as "PEG". It is a polymer compound formed by dehydration and condensation of ethylene glycol between molecules. Chemical formula HOCH2 (CH2OCH2) nCH2OH. Among them, n is greater than 4. The average molecular weight is between 200 and 7000. The number after polyethylene glycol represents the average molecular weight of the product. For example, polyethylene glycol-400 indicates that the average molecular weight of polyethylene glycol in this product is about 400.