Polymethyl methacrylate

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Structural formula
Polymethyl methacrylate
General
Surname Polymethyl methacrylate
other names
  • PMMA
  • Poly (methyl-2-methylpropenoate)
CAS number 9011-14-7
Monomer Methacrylic acid methyl ester
Molecular formula of the repeating unit C 5 H 8 O 2
Molar mass of the repeating unit 100.12 g mol −1
Type of polymer

Thermoplastic

properties
Physical state

firmly

density

approx. 1.18 to 1.19 g cm −3

Glass temperature

approx. 105 ° C

Water absorption

0.3% in dry air
1.2% in moist air
2% in water storage

solubility

not resistant to polar solvents such as B. acetone

Thermal expansion coefficient

70–85 10 −6  K −1 for semi-finished products below the glass transition temperature

safety instructions
GHS labeling of hazardous substances
no classification available
H and P phrases H: see above
P: see above
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Polymethylmethacrylate ( abbreviation PMMA , and acrylic glass ) is a transparent thermoplastic plastic .

history

Acrylic glass was developed around the same time in Germany , Great Britain and Spain in 1928 . In Germany, the chemist Walter Bauer (1893–1968) was involved in this. The first cast acrylic glass panes were manufactured by Otto Röhm in Germany in 1933 and brought to market maturity. The first contact lenses from plastic were 1,940 Heinrich Wöhlk made of PMMA and applied self-experimentation - by this time there were only lenses made of polished silicate glass which had a significantly poorer fit. One of the first mainstream products of PMMA were covers of the Radio - record player combinations Braun SK 4 of the 1956th

Polymethyl methacrylate is now used in large quantities for a wide range of applications (see below).

Manufacturing

PMMA is routinely produced in a radical manner by substance , emulsion or suspension polymerisation. PMMA produced in this way is atactic and completely amorphous . An anionic polymerization (including methods of living polymerization ) of PMMA is also possible.

Synthesized by radical polymerization

The following reactions take place, for example, with dibenzoyl peroxide as initiator :

1. Radical formation

Since organic peroxides disintegrate homolytically when little heat is supplied, they are very suitable as radical generators. First, dibenzoyl peroxide is split before carbon dioxide (CO 2 ) is separated from the resulting radicals :

Dibenzoyl peroxide decomposition

2. Chain start

The resulting radical now reacts with methyl methacrylate (MMA) to form a new, larger radical.

PMMA-Start.svg

3. Chain growth

When the chain grows, the radical formed when the chain starts reacts again with the methacrylic acid methyl ester. This reaction happens again and again, so that an ever larger radical is created.

PMMA growth

4. Chain termination

The chain growth can break off in different ways: two growing chains can meet and combine or disproportionate, or a growing chain can react with a starter radical. The first possibility is shown here:

PMMA-Abbruch.svg
The 10 meter deep display aquarium Monterey Bay is made of acrylic windows with a thickness of up to 33 centimeters to withstand the water pressure.
Lichtenberg figure in an acrylic polymer block

Structure and properties

Structure of polymethyl methacrylate

The pressure, temperature profile and duration of the polymerisation process have an influence on the average length of the resulting polymer chains and the crosslinking and entanglement of the polymer chains with one another. This, in turn, has a direct impact on some physical and chemical properties which, depending on the production process, may vary slightly from the values ​​listed below.

PMMA burns crackling, with a yellowish flame, sweetish smell, dripping and without residue. When knocked on with your fingernail, PMMA does not sound tinny compared to transparent polystyrene because of its lower hardness.

PMMA is plastically deformable beyond 100 ° C and this deformation is thermally reversible . It enables good machining, can be cut or engraved very well with CO 2 lasers and is less sensitive to scratches than other thermoplastics . Connections by gluing or welding are possible. It transmits light better than mineral glass , is easy to color, weather and aging resistant, resistant to acids , alkalis of medium concentration, petrol and oil . However, ethanol , acetone and benzene attack PMMA. Therefore acrylic glass surfaces must not be cleaned with alcohol or solvents , otherwise stress corrosion cracking occurs. It absorbs UV light (apart from special UV-permeable variants for use in X-ray lithography or for solariums ).

The good weathering stability of the methacrylate polymers is due to the purely aliphatic structure and the steric shielding of the polymer chain.

If further monomers (alkyl or aryl methacrylates) are used in the polymerization, it is possible to adapt the properties of the copolymer to the product requirements. For example, the heat resistance or the glass transition temperature can be influenced by a suitable choice of the alcohol radical of the monomeric ester : Long-chain esters such as lauryl and stearyl methacrylates already show waxy polymer properties; Esters with a strongly branched alcohol residue produce polymers with a reduced solution viscosity. Are used in the copolymerization of multifunctional acrylates such as ethylene glycol , are used, be cross-linking PMMA copolymers obtained which have modified properties and z is. B. differ significantly in the flexural strength , the modulus of elasticity or the abrasion resistance and can thus be adapted to the respective purposes.

Copolymer combinations of anionic and cationic PMMA result in interpolyelectrolyte complexes (IPEC). They are preferably used to encase medicinal substances and to release them in a well-defined manner.

The design options are also very diverse. It can not only be used as a glass replacement for windows, but also for household items such as bowls .

Technical properties of PMMA:

use

A sample of the poisonous and highly corrosive chemical element bromine , which had to be melted into a glass ampoule beforehand so that it cannot react with the PMMA , which was poured into PMMA for illustrative purposes and for teaching purposes .
Measuring cup made of PMMA (Plexiglas) with cracks caused by ethanol.

Polymethyl methacrylate is used to manufacture a large number of transparent and non-transparent objects, goods , components , semi-finished products and semi-finished products for use in a wide variety of areas . PMMA is e.g. B. Indispensable in dentistry , where it is used for prostheses . For this purpose, the plastic is coated with various inorganic and organic pigments , such as B. titanium dioxide , various iron oxides or azo pigments , so that the typical pink color is created. In a transparent form, it is used for bandage splints. The plastic is freely mixed and hardens under heat and pressure. It is also possible to add activators which allow polymerization without an external increase in pressure and temperature.

Overview of important areas of application:

  • Material for laser cutter
    • Sheets of extruded acrylic are better for cutting, and sheets of cast acrylic are better for engraving.

Brand and trade names

Broken PMMA windshield of a German aircraft from WWII

Polymethyl methacrylate (PMMA) became known under the trade name Plexiglas , registered in 1933 by Otto Röhm . In Europe and Asia, Plexiglas is a registered brand name of Röhm GmbH , in the USA it is Altuglas International ( Arkema Group). However, Röhm also sells its acrylic glass in the USA under the name Acrylite® .

In Europe, the Altuglas International Group markets PMMA under the name Altuglas ; Arkema Group PMMA under the name Oroglas .

Polymethyl methacrylate is also known colloquially as acrylic glass or O-glass. O-glass was the brand name of the material in the GDR (for "organic glass"). The only manufacturer was the Piesteritz nitrogen works . The trade name Piacryl is derived from "Piesteritz" .

There are a number of other proprietary trade names, including Biacryl , Conacryl , Deglas , deacon , Friacryl , Hesaglas , hesalite , Hesalite , Limacryl , PerClax and vitroflex .

recycling

Recycling code for polymethyl methacrylate and others

The recycling code for polymethyl methacrylate is 07.

See also

Other plastics for transparent applications:

literature

  • Kai Buchholz, Ralf Beil (ed.): Plexiglas®. Material in Architecture and Design (on the occasion of the exhibition Plexiglas, Material in Architecture and Design. Institut Mathildenhöhe Darmstadt, Museum Künstlerkolonie, September 16, 2007 - January 6, 2008. Translated by RAG Service, Sprachendienst). Wienand, Cologne 2007, ISBN 978-3-87909-925-2 .

Web links

Individual evidence

  1. ^ Wolfgang Kaiser, Kunststoffchemie für Ingenieure , 3rd edition, Carl Hanser, Munich, 2011, pp. 353f.
  2. ^ A b c Wolfgang Kaiser: Kunststoffchemie für Ingenieure , 3rd edition, Carl Hanser, Munich, 2011, 339ff.
  3. a b PMMA XT. Acrylic glass extruded. (PDF; 32 kB) In: Technical data sheet. Amsler & Frey AG (Schinznach-Dorf), August 1, 2016, p. 1 , accessed on April 5, 2018 .
  4. a b c Properties of plexiglass. GS / XT. In: plexiglas.de. Evonik, accessed April 5, 2018 .
  5. How great is the thermal expansion of acrylic? with online calculation. In: pmma.dk. Induflex (Stvring, Denmark), accessed April 5, 2018 .
  6. Alexander Unger: Term: coefficient of thermal expansion. Data from the book A. Unger: Fussboden-Atlas 2011. In: fussbodenatlas.de. Unger, accessed April 5, 2018 .
  7. This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
  8. Company - History. Wöhlk Contactlinsen GmbH, accessed on March 26, 2018 .
  9. ^ Rauch Puntigam, Theodor Volker: Acrylic and methacrylic compounds . In: Springer Verlag Berlin (ed.): Chemistry, physics and technology of plastics in individual representations . tape 9 . Springer Verlag, 1967, ISBN 978-3-642-46058-6 , pp. 208 ff .
  10. ^ Diego Gallardo, Brigitte Skalsky, Peter Kleinbudde: Characterization of combinations between anionic-cationic poly (methyl methacrylate) copolymers. In: Die Pharmazeutische Industrie , Volume 73, No. 10, 2011, pp. 1875-1884.
  11. a b Degussa Röhm Plexiglas product description, identification no. 211-1, Feb. 2003.
  12. ^ Philipp Gellius:  Musical instruments made of plexiglass. Signals for the musical world , year 1938, p. 479f. (Online at ANNO ).Template: ANNO / Maintenance / smw
  13. ^ History on plexiglas.de
  14. Registered 2006-05 as a community trademark under number 003739505
  15. ^ Altuglas International .
  16. Oroglas .