Editing Poly(methyl methacrylate) (section)

== Properties ==
[[File:Methyl-methacrylate-skeletal.svg|thumb|left|upright=0.5|Skeletal structure of methyl methacrylate, the constituent [[monomer]] of PMMA]]
[[File:Perspex pieces (AM 2007.10.2-2).jpg|thumb|Pieces of Plexiglas taken from the windscreen of a German plane shot down during World War II]]

PMMA is a strong, tough, and lightweight material. It has a [[density]] of 1.17–1.20&nbsp;g/cm{{sup|3}},<ref name=p1/><ref name=p2/> which is approximately half that of glass, which is generally, depending on composition, 2.2–2.53&nbsp;g/cm{{sup|3}}.<ref name=p1>[http://www.makeitfrom.com/material-properties/Polymethylmethacrylate-PMMA-Acrylic Polymethylmethacrylate (PMMA, Acrylic)] {{webarchive|url=https://web.archive.org/web/20150402124133/http://www.makeitfrom.com/material-properties/Polymethylmethacrylate-PMMA-Acrylic |date=2015-04-02}}. Makeitfrom.com. Retrieved 2015-03-23.</ref> It also has good impact strength, higher than both glass and polystyrene, but significantly lower than polycarbonate and some engineered polymers. PMMA ignites at {{cvt|460|C}} and [[combustion|burns]], forming [[carbon dioxide]], [[water]], [[carbon monoxide]], and low-molecular-weight compounds, including [[formaldehyde]].<ref>{{cite journal |id={{INIST|14365060}} |doi=10.1177/073490402762574749 |title=Preliminary Studies on Burning Behavior of Polymethylmethacrylate (PMMA) |year=2002 |last1=Zeng |first1=W. R. |last2=Li |first2=S. F. |last3=Chow |first3=W. K. |journal=Journal of Fire Sciences |volume=20 |issue=4 |pages=297–317|hdl=10397/31946 |s2cid=97589855 |hdl-access=free}}</ref>

PMMA [[transmittance|transmits]] up to 92% of [[visible light]] ({{cvt|3|mm}} thickness),<ref>{{cite book |last1=McKeen |first1=Laurence W. |title=The effect of UV light and weather on plastics and elastomers |date=2019 |publisher=Elsevier |location=Washington, WA |isbn=978-0-1281-6457-0 |page=254 |edition=4th |url=https://app.knovel.com/kn/resources/kpEUVLWP11/toc}}</ref> and gives a reflection of about 4% from each of its surfaces due to its [[refractive index]] (1.4905 at 589.3{{nbsp}}nm).<ref name=refr>[http://refractiveindex.info/?shelf=organic&book=poly%28methyl_methacrylate%29&page=Szczurowski Refractive index and related constants – Poly(methyl methacrylate) (PMMA, Acrylic glass)] {{webarchive|url=https://web.archive.org/web/20141106114447/http://refractiveindex.info/?shelf=organic&book=poly%28methyl_methacrylate%29&page=Szczurowski |date=2014-11-06}}. Refractiveindex.info. Retrieved 2014-10-27.</ref> It filters [[ultraviolet]] (UV) light at wavelengths below about 300 [[nanometre|nm]] (similar to ordinary window glass). Some manufacturers<ref>[http://www.plexiglas.com/acrylicsheet/acrylicsheetfamily#9 Altuglas International Plexiglas UF-3 UF-4 and UF-5 sheets] {{webarchive|url=https://web.archive.org/web/20061117051151/http://www.plexiglas.com/acrylicsheet/acrylicsheetfamily |date=2006-11-17}}. Plexiglas.com. Retrieved 2012-05-09.</ref> add coatings or additives to PMMA to improve absorption in the 300–400&nbsp;nm range. PMMA passes [[infrared]] light of up to 2,800&nbsp;nm and blocks IR of longer [[wavelength]]s up to 25,000&nbsp;nm. Colored PMMA varieties allow specific IR wavelengths to pass while blocking [[visible spectrum|visible light]] (for [[remote control]] or heat sensor applications, for example).

PMMA swells and dissolves in many organic [[solvent]]s; it also has poor resistance to many other chemicals due to its easily [[hydrolysis|hydrolyzed]] [[ester]] groups. Nevertheless, its environmental stability is superior to most other plastics such as polystyrene and polyethylene, and therefore it is often the material of choice for outdoor applications.<ref>Myer Ezrin [https://books.google.com/books?id=baWyaC3w3hcC&pg=PA168 ''Plastics Failure Guide: Cause and Prevention''] {{webarchive|url=https://web.archive.org/web/20160421165428/https://books.google.com/books?id=baWyaC3w3hcC&pg=PA168 |date=2016-04-21}}, Hanser Verlag, 1996 {{ISBN|1-56990-184-8}}, p. 168</ref>

PMMA has a maximum water absorption ratio of 0.3–0.4% by weight.<ref name=p2>[http://www.matbase.com/material/polymers/commodity/pmma/properties DATA TABLE FOR: Polymers: Commodity Polymers: PMMA] {{webarchive|url=https://web.archive.org/web/20071213163116/http://www.matbase.com/material/polymers/commodity/pmma/properties |date=2007-12-13}}. Matbase.com. Retrieved 2012-05-09.</ref> Tensile strength decreases with increased water absorption.<ref>{{cite journal |doi=10.1557/PROC-875-O12.7 |first1=Chiemi |last1=Ishiyama |first2=Yoshito |last2=Yamamoto |first3=Yakichi |last3=Higo |year=2005 |title=Effects of Humidity History on the Tensile Deformation Behaviour of Poly(methyl–methacrylate) (PMMA) Films |journal=MRS Proceedings |volume=875 |editor1-first=T. |editor1-last=Buchheit |editor2-first=A. |editor2-last=Minor |editor3-first=R. |editor3-last=Spolenak |editor4-first=K. |display-editors=3 |editor4-last=Takashima |pages=O12.7}}</ref> Its [[coefficient of thermal expansion]] is relatively high at (5–10)×10{{sup|−5}}&nbsp;°C{{sup|−1}}.<ref>{{cite web |title=Tangram Technology Ltd. – Polymer Data File – PMMA |url=http://www.tangram.co.uk/TI-Polymer-PMMA.html |url-status=live |archive-url=https://web.archive.org/web/20100421184714/http://www.tangram.co.uk/TI-Polymer-PMMA.html |archive-date=2010-04-21}}</ref>

The [[Futuro]] house was made of fibreglass-reinforced polyester plastic, polyester-polyurethane, and poly(methylmethacrylate); one of them was found to be degrading by [[cyanobacteria]] and [[Archaea]].<ref>{{cite journal |doi=10.1016/j.tibtech.2006.06.001 |title=Biodeterioration of modern materials in contemporary collections: Can biotechnology help? |year=2006 |last1=Cappitelli |first1=Francesca |last2=Principi |first2=Pamela |last3=Sorlini |first3=Claudia |journal=Trends in Biotechnology |volume=24 |issue=8 |pages=350–4 |pmid=16782219}}</ref><ref>{{cite journal |doi=10.1038/sj.embor.7400844 |title=Saving a fragile legacy. Biotechnology and microbiology are increasingly used to preserve and restore the world's cultural heritage |year=2006 |last1=Rinaldi |first1=Andrea |journal=EMBO Reports |volume=7 |issue=11 |pages=1075–9 |pmid=17077862 |pmc=1679785}}</ref>

PMMA can be joined using [[cyanoacrylate]] cement (commonly known as [[superglue]]), with heat (welding), or by using chlorinated solvents such as [[dichloromethane]] or [[chloroform|trichloromethane]]<ref>[http://www.science-projects.com/Plastics/PlexiglasWork.htm "Working with Plexiglas"] {{webarchive|url=https://web.archive.org/web/20150221110921/http://www.science-projects.com/Plastics/PlexiglasWork.htm |date=2015-02-21}}. ''science-projects.com''.</ref> (chloroform) to dissolve the plastic at the joint, which then fuses and sets, forming an almost invisible [[solvent welding|weld]]. Scratches may easily be removed by polishing or by heating the surface of the material. [[Laser cutting]] may be used to form intricate designs from PMMA sheets. PMMA vaporizes to gaseous compounds (including its monomers) upon laser cutting, so a very clean cut is made, and cutting is performed very easily. However, the pulsed lasercutting introduces high internal stresses, which on exposure to solvents produce undesirable "stress-[[crazing]]" at the cut edge and several millimetres deep. Even ammonium-based glass-cleaner and almost everything short of soap-and-water produces similar undesirable crazing, sometimes over the entire surface of the cut parts, at great distances from the stressed edge.<ref name=hjsandersen>{{cite web |last1=Andersen |first1=Hans J |title=Tensions in acrylics when laser cutting |url=http://www.support.induflex.dk/Plast_Laserskaering_acryl.aspx?Lang=en-GB#lblTensions |access-date=23 December 2014 |url-status=live |archive-url=https://web.archive.org/web/20151208045021/http://www.support.induflex.dk/Plast_Laserskaering_acryl.aspx?Lang=en-GB#lblTensions |archive-date=8 December 2015}}</ref> Annealing the PMMA sheet/parts is therefore an obligatory post-processing step when intending to chemically bond lasercut parts together.

In the majority of applications, PMMA will not shatter. Rather, it breaks into large dull pieces. Since PMMA is softer and more easily scratched than glass, [[anti-scratch coating|scratch-resistant coatings]] are often added to PMMA sheets to protect it (as well as possible other functions).

Pure poly(methyl methacrylate) homopolymer is rarely sold as an end product, since it is not optimized for most applications. Rather, modified formulations with varying amounts of other [[comonomer]]s, additives, and fillers are created for uses where specific properties are required. For example:

* A small amount of acrylate comonomers are routinely used in PMMA grades destined for heat processing, since this stabilizes the polymer to [[depolymerization]] ("unzipping") during processing.
* Comonomers such as [[butyl acrylate]] are often added to improve impact strength.
* Comonomers such as methacrylic acid can be added to increase the glass transition temperature of the polymer for higher temperature use such as in lighting applications.
* [[Plasticizer]]s may be added to improve processing properties, lower the glass transition temperature, improve impact properties, and improve mechanical properties such as elastic modulus <ref>{{cite journal |last1=López |first1=Alejandro |last2=Hoess |first2=Andreas |last3=Thersleff |first3=Thomas |last4=Ott |first4=Marjam |last5=Engqvist |first5=Håkan |last6=Persson |first6=Cecilia |date=2011-01-01 |title=Low-modulus PMMA bone cement modified with castor oil |journal=Bio-Medical Materials and Engineering |language=en |volume=21 |issue=5–6 |pages=323–332 |doi=10.3233/BME-2012-0679 |pmid=22561251 |issn=0959-2989 |doi-access=free}}</ref>
* [[Dye]]s may be added to give color for decorative applications, or to protect against (or filter) UV light.
* [[Filler (materials)|Fillers]] may be substituted to reduce cost.