CHEM 121 glossary

Polyethylene

The addition polymer of ethene, $\left[\,\ce{CH2-CH2}\,\right]_n$ , the most widely made plastic. Branched LDPE (low-density) is soft and used for bags and film; linear, more crystalline HDPE (high-density) is stiffer and used for jugs and pipes.

The monomer, ethene: its C=C is used up, so the polymer is saturated.

Example

A polyethylene chain of molar mass $5.6 \times 10^5$ g/mol contains $5.6 \times 10^5 / 28.05 \approx 2.0 \times 10^4$ $\ce{C2H4}$ repeat units.