Editing Polyethylene (section)

===Low-density (LDPE)===
{{Main|Low-density polyethylene}}
LDPE is defined by a density range of 0.910–0.940&nbsp;g/cm<sup>3</sup>. LDPE has a high degree of short- and long-chain branching, which means that the chains do not pack into the [[crystal structure]] as well. It has, therefore, less strong intermolecular forces as the [[instantaneous-dipole induced-dipole attraction]] is less. This results in a lower [[tensile strength]] and increased [[ductility]]. LDPE is created by [[Radical polymerization|free-radical polymerization]]. The high degree of branching with long chains gives molten LDPE unique and desirable flow properties. LDPE is used for both rigid containers and plastic film applications such as plastic bags and film wrap.

The radical polymerization process used to make LDPE does not include a catalyst that "supervises" the radical sites on the growing PE chains. (In HDPE synthesis, the radical sites are at the ends of the PE chains, because the catalyst stabilizes their formation at the ends.) Secondary [[free radical|radicals]] (in the middle of a chain) are more stable than primary radicals (at the end of the chain), and tertiary radicals (at a branch point) are more stable yet. Each time an ethylene monomer is added, it creates a primary radical, but often these will rearrange to form more stable secondary or tertiary radicals. Addition of ethylene monomers to the secondary or tertiary sites creates branching.