Illustrated Glossary of Organic Chemistry

Methacrylic acid: The α,β-unsaturated carboxylic acid having the molecular structure shown below. IUPAC name 2-methyl-prop-2-enoic acid. The methacrylate group is a piece of molecular structure equal to Methacrylic acid minus the carboxylic acid proton. A methacrylate is a molecular structure containing a methacrylate group. Polymerization of methyl methacrylate yields poly(methyl methacrylate), also known as Plexiglas.

Molecular structure of methacrylic acid.   
Methacrylate group
Methyl methacrylate
The methacrylate group is shown in red
A glass tube of bromine embedded
in a Plexiglas block.