Polymethyl methacrylate is often used as a substitute for glass, and the properties of the substance are as follows: physical properties 1. The density of PMMA is lower than that of glass: the density of PMMA is about 1.15-1.19g/cm3, which is half of glass (2.40-2.80g/cm3) and 43% of metal aluminum (belongs to light metal). 2. The mechanical strength of PMMA is relatively high: the relative molecular mass of PMMA is about 2 million, it is a long-chain polymer, and the chain forming the molecule is very soft. Therefore, the strength of PMMA is relatively high, and it is resistant to stretching and impact. Its capacity is 7 to 18 times higher than that of ordinary glass. There is a kind of plexiglass that has been heated and stretched, in which the molecular segments are arranged in a very orderly manner, so that the toughness of the material is significantly improved. The plexiglass is driven with a nail, and even if the nail penetrates, it will not crack. This kind of plexiglass is also not broken into pieces after being penetrated by a bullet. Therefore, stretch-treated PMMA can be used as bulletproof glass and also as canopy on military aircraft. 3. The melting point of PMMA is lower, which is much lower than the high temperature of glass of about 1000 degrees. 4. The transmittance of PMMA is higher (1) Visible light: PMMA is the best polymer transparent material at present, with a light transmittance of 92%, which is higher than that of glass. (2) Ultraviolet light: Quartz can completely transmit ultraviolet rays, but the price is high, and ordinary glass can only transmit 0.6% of ultraviolet rays. PMMA can effectively filter out ultraviolet light with a wavelength less than 300nm, but the filtering effect between 300nm and 400nm is poor. Some manufacturers coat the surface of PMMA to increase its ability to filter out 300nm to 400nm UV light. On the other hand, PMMA has better stability than polycarbonate when exposed to UV light (3) Infrared: PMMA allows infrared (IR) with a wavelength of less than 2800nm to pass. Longer wavelengths of IR, less than 25,000 nm, can be substantially blocked. There are special colored PMMAs that allow specific wavelengths of IR to pass through while blocking visible light (for remote control or thermal sensing, etc.). (4) The glass transition temperature of PMMA is about 105°C. Its molding methods include casting, injection molding, machining, thermoforming, etc. In particular, injection molding can be mass-produced, with simple process and low cost. Therefore, its application is becoming more and more extensive, and it is widely used in instrumentation parts,automobile lights, optical lenses, and transparent pipes.