Polymethacrylates are amorphous commodity thermoplastics
of high transparency that can be easily processed and converted into many semi-finished products like films,
rods, tubes, and sheets. The most commercially important methacrylate polymer is poly(methyl methacrylate) (PMMA)
also known as Plexiglas, Lucite, Acrylite, and Altuglas. It is a
high volume amorphous thermoplastic with high Tg (398 K), good mechanical properties
and excellent weatherability. It is resistant to oils, alkanes and (diluted) acids but
is not resistant to many (polar) solvents such as alcohols, organic acids and ketones.
It is also rather brittle and has low impact strength and fatigue resistance. To increase its toughness, PMMA is often modified with core-shell rubber or other impact modifers. These resins offer
upto 10 times the impact resistance of standard PMMA while maintaining high
clarity.
Because of their high transparency (92% transmission),
toughened acrylics are often used as a lightweight and
shatter-resistant replacement for regular glass. These resins have sufficient impact resistance to be machined.
Most commercial grades are polymerized by free radical initiators such as peroxides and azo compounds, yielding atactic polymers. PMMA can be also polymerized anionically, yielding syndiotactic and isotactic polymers. Most commercial grades of PMMA, however, are atactic. The glass transition temperature of atactic PMMA is 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).
Some other important
methacylates include methacrylic
acid (MAA), N-butyl-methacrylate (n-BMA)2, iso-butyl methacrylate
(i-BMA)2, cyclohexyl methacrylate (CHMA), ethyl methacrylate
(EMA), 2-hydroxyethyl methacrylate, 2-ethylhexyl methacrylate (EHMA),
and ethylene glycol-based dimethacrylates
to name only a few. They are often copolymerized with MMA or
are used as chemical intermediates to increase
heat resistance, melt flow index, flexibility, crosslink
density (dimethacrylates) and impact strength of unmodifed PMMA
which is rather brittle. They are also used to improve the
paintability and printability as well as the compatibility with other compounds in a variety of products.
Poly(metylmethacylate) is sold under a variety of brand names. It is often called acrylic glass. Three important trade names for methacrylate polymer products and resins include
Acrylite®, Plexiglas®, and Lucite®, .
PMMA is an economical alternative to polycarbonate (PC) when 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 for light transmission, architectural structures, tail lights for cars, bathtubs and sanitary fixtures, to name only a few products.
A larger number of other polymethacrylates are commercially available. However, the total production volume is rather small compared to PMMA. These polymers are used in a variety of products, including elastomers, coatings, and semi-crash resistant adhesives3.
For example, poly(cyclohexyl methacrylate) finds uses in adhesives, binders, and coatings. Its glass transition temperature is similar to poly(methyl methacrylate). Another important methacylate polymer is poly(2-hydroxyethyl methacrylate) (HEMA). It is used in contact lenses, drug delivery systems, dental adhesives, and for several other biomedical applications.
Many other methacrylic monomers are commercially available and are used as building blocks to make a wide range of polymer-based products like binders in paints, coatings, toners, inks, and water-soluble polymers.
1Altuglas Plexiglas® brochure 'Acrylic Resins - Impact-Modified Resins'.
2N-BMA and i-BMA are of low(er) concern to human health and environment.
3Methacrylate
adhesives are not recommended for very demanding applications (e.g. aerospace or automotitv industry) due to air-inhibition
which results in insufficient cure when exposed to air. They also have lower bond and corrosion performance
than structural epoxy adhesives.