PMMI stands for polymethylmethacrylate Isomers (Poly(Methyl Methacrylate Isomers)) and usually refers to a polymer material that is similar to ordinary polymethyl methacrylate (PMMA, also known as acrylic or plexiglass), but contains different isomers in the molecular structure. PMMI has physical and optical properties similar to PMMA, but can have a higher glass transition temperature (Tg), providing better thermal stability and dimensional stability.

In the application of optical lenses, a higher glass transition temperature means that the material can remain morphological and dimensional stable over a wider temperature range, which is important for certain optical systems that need to operate at high temperatures. In addition, like PMMA, PMMI can also provide high light transmittance and low dispersion, which makes them suitable for manufacturing lenses, optical Windows, optical guides, and other visually transparent components.

However, please note that PMMI may not be a very common term or widely used material, so in practical applications, it may be necessary to pay special attention to the specific performance and application recommendations provided by the material supplier when referring to PMMI.