Abstract

Low density polyethylene (LDPE) was the first thermoplastic polyolefin used commercially. It was discovered serendipitously in 1933 and was quickly utilized for radar sheathing during the war. LDPE, along with high density polyethylene (HDPE) and linear low density polyethylene (LLDPE), offers an unparalleled combination of low cost, ease of fabrication into a variety of end uses, and balance of physical properties. Polyethylene has displaced paper, metal, wood, and other materials of construction. LDPE is unique in its polymerization process. Free-radical-initiated polymerization is used to make LDPE, as compared to transition-metal catalysis for HDPE and LLDPE. The free-radical process leads to the unique molecular structure of LDPE: the presence of long-chain branching. The long-chain branching imparts unusual rheological behavior in both shear and extension. LDPE is used in a variety of applications, such as film, coating, molding, and wire and cable insulation. One of the reasons for its wide range of utility is its thermal stability and low toxicity.