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PMMA ignites at 460 °C (860 °F) and burns, forming carbon dioxide, water, carbon monoxide, and low-molecular-weight compounds, including formaldehyde. [17] PMMA transmits up to 92% of visible light (3 mm (0.12 in) thickness), [18] and gives a reflection of about 4% from each of its surfaces due to its refractive index (1.4905 at 589.3 nm). [3]
For the first fifty years, glass was the only material used. The lenses were thin, yet reports of injury were rare. In 1938 perspex (polymethylmethacrylate, or PMMA) began to replace glass in contact lens manufacture. PMMA lenses were easier to produce so the production of glass lenses soon ended. Lenses made of PMMA are called hard lenses. [5]
The development of polymethyl methacrylate (PMMA) in the 1930s paved the way for the manufacture of plastic scleral lenses. In 1936, optometrist William Feinbloom introduced a hybrid lens composed of glass and plastic, [ 21 ] and in 1937 it was reported that some 3,000 Americans were already wearing contact lenses. [ 22 ]
Poly(methyl acrylate) (PMA) is a family of organic polymers with the formula (CH 2 CHCO 2 CH 3) n.It is a synthetic acrylate polymer derived from methyl acrylate monomer. The polymers are colorless.
For many applications it has since been replaced by other methods for making PMMA such as extrusion, which gives uniform surface features. However, for applications where strength is critical cell casting techniques are still employed in conjunction with stretching, which produces a stronger overall material.
MMA was discovered by Bernhard Tollens and his student W. A. Caspary in 1873, [5] who noticed and described its tendency to change into a clear, hard, transparent substance especially in sunlight. [6]
The federal judge hearing arguments over whether tech billionaire Elon Musk's role at the Department of Government Efficiency is unconstitutional indicated that she will not issue a ruling Friday ...
Poly(methyl methacrylate) (PMMA) This page was last edited on 3 November 2024, at 13:35 (UTC). Text is available under the Creative Commons Attribution ...
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