2-hydroxyethyl methacrylate

2-hydroxyethyl methacrylate, commonly known as HEMA, is a clear liquid compound used to create polymers. It is derived from methacrylic acid and ethylene or propylene oxide.12

HEMA is particularly notable for its use in making soft contact lenses. When HEMA polymerizes, it forms polyHEMA, a plastic that can absorb a significant amount of water, up to 60% of its weight. This creates a soft hydrogel with optical qualities similar to hard contact lenses but with less irritation to the eye. While polyHEMA lenses were dominant in the 1960s and 1970s, other water-absorbing plastics, some based on HEMA, have been developed since the 1980s.1

It is important to distinguish this HEMA from the combining form "hema-" which relates to blood, derived from the Greek word haima.3