Polymethacrylates (PMMA, Plexiglas)
Properties and Applications
Polymethyl methacrylate (PMMA), also known as acrylic or plexiglas, is a high volume amorphous, transparent and colorless commodity thermoplastic that can be easily processed and converted into many finished and semi-finished products.
Most commercial grades of PMMA are polymerized by free radical polymerization, yielding atactic polymers whereas anionic polymerization yields syndiotactic or isotactic polymers. Most commercial grades of PMMA, however, are atactic with a glass transition temperature of 398 K (125 °C).
Commercial PMMA is often copolymerized with comonomers other than methyl methacrylate. The Tg of these products can vary, ranging broadly from approximately 360 K to 430 K (87 to 157 °C).
PMMA is known for its stiffness, hardness and excellent weatherability. Unmodified PMMA, however, is rather brittle and has low impact strength and fatigue resistance. To increase its toughness, it is often modified with core-shell rubber or other impact modifers. These resins offer seven to 10 times the impact resistance of standard PMMA while maintaining high transparency.1
Because of its high transparency (92% transmission) PMMA can be used as a lightweight and shatter-resistant replacement for regular glass. It has sufficient impact resistance to be machined and is often an economical alternative to polycarbonate (PC) when very high toughness and impact strength is not required. It comes in a variety of forms such as sheets, rods, and tubes, and is used for signs, optical fibers, architectural structures, tail lights for cars, bathtubs and sanitary fixtures, to name only a few applications.
Many other methacrylic monomers are commercially available. They are either copolymerized with methyl methacrylate to improve its properties or are added to many other resin systems to make a wide range of polymer-based products like binders in paints, coatings, toners, inks, and water-soluble polymers.