Acrylic patented 90 years ago

In the course of the 1930s, the first glass-like objects made from polymethyl methacrylate (PMMA) came onto the market in Germany. Thanks to their many different advantages, they were strong competition for products made from conventional glass, particularly in aircraft and car manufacturing. The fact that demand for acrylic very soon went through the roof and enabled Röhm & Haas, the sole supplier in Germany, to set sales records was attributable to a very large extent to the rearmament policy adopted by the Nazi regime. Although the government contracts were lucrative, company director Otto Röhm personally suffered from the Nazi dictatorship. Enemy bombing during the war finally brought production to a standstill. This did not stop acrylic from continuing its triumphant success: in the course of the “economic miracle” experienced in West Germany, it enjoyed a comeback in such products as those given the nickname “Schneewittchensarg” (“Snow White’s coffin”), while East Germany manufactured acrylic of its own at a production location that specialised in PMMA.

At the end of the 1920s, research carried out in-house at “Röhm & Haas” in Darmstadt reached such an advanced stage that polymethyl methacrylate (PMMA) was ready to be launched on the market. The chemists involved – and the company management – were delighted with their achievement, because they had beaten their overwhelmingly powerful competitor I.G. Farben to it: PMMA promised good business, because the new thermoplastic had numerous properties that made it superior to both polyacrylate (PA) and glass and gave it a wide range of possible applications as a result:

• Polymethyl methacrylate vs. polyacrylate: “Technologically speaking, there is such a great and striking difference between acrylate and methacrylate polymers, because polymethacrylic acid methyl ester is a hard, glass-like material at room temperature, whereas the corresponding polyacrylic ester is a tough rubber” (Trommsdorff 1976, 227). The latter only sets at temperatures below 0°C, while “polymer methyl ester is the hardest polymer with the highest softening point” (Trommsdorff 1976, 232), i.e. it remains dimensionally stable up to about 100°C. “At 140-160°C, acrylic assumes properties similar to soft rubber and turns hard and dimensionally stable again on cooling, when it maintains the shape that it has been given when heated” (Trommsdorff 1976, 237; cf. Trommsdorff 1937, 8). “Very high-molecular polymethyl methacrylate is still as tough as rubber at temperatures of about 200°C” (Trommsdorff 1937, 5). The fundamental difference between PMMA and PA is attributable to “the higher chain stiffness of the polymethacrylate molecules compared with the higher flexibility of the polyacrylate chain” (Trommsdorff 1976, 227). 
  
  
• Organic glass (basis; carbon) vs. inorganic glass (basis: silicate): “Acrylic is an organic glass that shares the clear transparency of silicate glass, but has the advantages over silicate glass of a lower specific weight, higher mechanical strength and easier formability / processability. It has the disadvantage of lower surface hardness, which is not of much consequence, however, because it is easy to polish”: this is the summary given by Trommsdorff 1937, 9. The main advantage of acrylic apart from high resistance to breakage (impact resistance), which is roughly seven times that of silicate glass (Röhm & Haas 1938, 12 and Edschmid 1957, 54) is its low weight: 

“Acrylic is light, to be exact it weighs less than half of conventional glass. Its specific weight is 1.18, compared with 2.6 for silicate glass. This means that acrylic satisfies very effectively the urgent demands for weight savings made by modern technology. One example: the panes of silicate glass with the standard thickness of 5.5 mm that are used for the roofs and rear windscreen of a bus weigh about 80 kg. The same panes made from acrylic that is 3 mm thick (this thickness is sufficient in view of the high breakage resistance of the material) weigh only about 20 kg, however. A weight reduction means, however […] an increase in the maximum possible load, higher speed and lower fuel consumption, i.e.: greater economic viability” (Röhm & Haas 1938, 10). 

Organic glass performs better where optical properties are concerned too: “Its light permeability level of 92% is […] higher than that of conventional window glass – even a block of PMMA 6 m thick would still let 50% of incident light through” (Buchholz 2007, 107). Not to mention substantially greater permeability to ultraviolet radiation and X-rays (Röhm & Haas 1938, 4-5). 

Acrylic frequently performs better in comparisons with other plastics as well. The qualities that are emphasised are its resistance to light, weathering and ageing, in other words: it does not turn yellow and it does not go brittle or form cracks (Röhm & Haas 1938, 14). Buchholz 2007, 127 qualifies this: “Although the UV radiation that sunlight contains can lead to the breakage of individual chains in PMMA too, acrylic glass is particularly resistant to weathering when compared with other materials. A long-term trial under Central European climatic conditions that lasted 25 years showed that […] its resistance to breakage is not influenced […] by weathering. Impact testing produced comparable results, which were in actual fact identical to the figures recorded with unweathered materials”. 

Although organic glass is combustible, it is highly non-flammable, i.e. it is not a fire risk – in contrast to celluloid, which is also transparent (Röhm & Haas 1938, P. 14). “Lyes of any concentration” and “most disinfectants and cleaning agents” cannot harm it. The same is true of water, sea water, saline solutions and even petrol, mineral oil, turpentine and diesel oil. It is, on the other hand, attacked by acids and “alcohols, ketones, chlorinated hydrocarbons, benzene and benzene-like substances cause acrylic to swell or dissolve” (Röhm & Haas, 14 and 15).

Acrylic glass is versatile not least of all with respect to the options for processing it: in addition to moulding – i.e. forming without cutting – after it is heated, it can be processed by such cutting operations as sawing, milling, drilling, filing, carving, embossing, punching, engraving and grinding as well as by polishing and gluing (Trommsdorff 1937, 8 and Röhm & Haas 1938, 18). A veritable jack of (almost) all trades, although it goes without saying that it as a thermoplastic was not suitable for purposes involving higher temperatures. In the 1930s, for example, “efforts made […] to produce colourful plastic zips […], the individual links of which were applied directly onto the edge of a textile strip” failed “because of the need to manufacture products that could withstand boiling” (Trommsdorff 1976, 246; cf. Trommsdorff 1937, 11). 

Since it was highly transparent, resisted breakage and weighed little, PMMA was an obvious substitute for glass. And this was precisely the heading given to German Imperial Patent (DRP) 724229 too, which Röhm & Haas obtained on 22. March 1932 – as an addition to the main patent DRP 656421 of 7. February 1928 (“Plastics formed from polyacrylic acid, its compounds or blends of the same”). A new feature was that the additional patent claimed “the use of copolymers made from acrylic acid and methacrylic acid esters” for the production of a glass substitute and justified this as follows: 

“It has been determined that copolymers made from acrylic acid esters and methacrylic acid esters are particularly suitable as a substitute for glass instead of the polymerisation products of acrylic acid and/or their functional derivatives. The copolymers are obtained by joint polymerisation of the monomer source materials. In contrast to such familiar glass substitutes as panes of celluloid, the glass substitute produced in accordance with this invention is extremely resistant to light, moisture, petrol, oil and other substances, is very permeable to ultraviolet light and has excellent mechanical properties, e.g. elasticity and toughness, even at low temperatures. The copolymers are, in addition, substantially harder than the polymer blends that are the subject of the main patent. They also have the advantages over them of being clear and streak-free, of having more consistent mechanical properties and of being more optically homogeneous”.

In view of the “unusually large number of desirable properties that this new material has to offer for the first time” (Röhm & Haas 1938, 21), it was considered to be a promising candidate for large-scale industrial use – and thus for a wide range of different products. Röhm & Haas started “with the production of thin discs that attracted interest for gas masks and clocks/watches as early as 1933” (Trommsdorff 1976, 235). They were soon followed by optically ground glass for spectacles “with any required dioptre” (Röhm & Haas 1938, 5), which were particularly suitable for protective glasses as well as for lenses, magnifying glasses and prisms due to their resistance to breakage (Buchholz 207, 107) and for drawing instruments and rulers (Trommsdorff 1976, 241). “Spectacle frames can also be made from this […] material; they are light and unobtrusive – since they are crystal clear – and are therefore pleasant to wear” (Röhm & Haas 1938, 13). 

“Physicists see potential uses of acrylic for insulation purposes, for equipment covers, for optical examinations or for transparent pipes in applications with demanding mechanical requirements” (Röhm & Haas 1938, 23). The new plastic did not attract much attention in these contexts initially, but this changed when it was put to everyday use from 1936 onwards in the form of such durable goods as cutlery, dessert bowls or butter dishes (Wittig 2007, 42; see also Trommsdorff 1976, 238 and Vaupel 2011, 28). In connection with this, the manufacturer stressed that the “outstanding insulation properties” of acrylic stopped it getting hot quickly, which was “a major advantage” in the kitchen (Röhm & Haas 1938, 9). 

1936 was a key year in the acrylic success story in many different respects (cf. Trommsdorff 1976, 280). After Otto Röhm had made sure in discussions with experts which tended to be kept confidential “that acrylic could become his company’s most important product” (Wittig 2007, 40), he decided to go public for the first time (Trommsdorff 1976, 237): in July 1936, he went to Munich to present his organic glass to the trade community at the 49^th annual meeting of the Association of German Chemists (VDCh). Incidentally: during his presentation there, Röhm wore spectacles with octagonal ground lenses made of acrylic (Trommsdorff 1976, 238 and Wittig 2007, 54). His statements included the following explanations: 

“What is known as layered glass was invented […] in response to the need to eliminate the danger of splintering that is encountered with standard silicate glass. Above and beyond the combination of silicate glass with polymers, the speaker and his staff members Bauer and Weisert succeeded in going one stage further: eliminating silicate glass completely and producing purely organic glass (‘Plexiglas’). The source material for this is α-methacrylic acid, abbreviated as methacrylic acid (C₃H₅COOH). The esters of this acid are colourless liquids which readily change to a polymer state and solidify in this process. These solid materials become increasingly soft when higher alcohols are used to form the esters and vice-versa, i.e. the methyl ester produces the hardest polymer. […] The new ‘glass’ has already been used successfully in aircraft and cars for 2 years now instead of standard silicate glass and instead of multilayer safety glass” (Röhm 1936, 591). 

Political developments were particularly helpful in boosting sales potential: in the third year of the Nazi dictatorship, the state became the main buyer of acrylic and commandeered it for military purposes. The Minister of Aviation (Hermann Göring / 1893-1946) had decided that the new plastic was “economically valuable” (Edschmid 1957, 56); as the man responsible for the four-year plan of 18. October 1936, he also assigned it an important role – in the context of military rearmament, which the Nazi regime made no secret of: 

“1936 marked the beginning of a rapid development in military technology: Junkers completed its tests on the use of acrylic for aircraft cockpits successfully. Acrylic was officially approved and promoted for aviation purposes. […] On 17. August 1937, the Ministry of Aviation confirmed to Röhm & Haas ‘that the acrylic you have developed must be considered a valuable material for air force military technology; continued development of it and rapid expansion of the production of it should therefore be given particularly high priority’.” (Wittig 2007, 49)

Inclusion in the four-year plan facilitated initial marketing immensely (Wittig 2007, 61) and “made the company’s position considerably stronger than its large industrial competitors and led to lucrative defence contracts” (Wittig 2007, 49). The “years when acrylic was an innocent material“ were over, however. “Röhm & Haas became an armaments company” (Wittig 2007, 49) – very much as planned by the company management, which had taken action itself at an early stage to generate economic benefits: “Röhm tried to sell his products to the Deputy Trustee of Labour for the Hesse region and he also encouraged an employee of his company to take advantage of his contacts to the Ministry of Aviation. Apart from this, Röhm & Haas took opportunities to present acrylic to senior representatives of the government at the major national and international exhibitions” (Wittig 2007, 49). Even the Bayreuth Festival had been used to establish contact with the government as early as 1935, with the aim of securing air force contracts. Winifred Wagner (1897-1980), the well-connected posthumous daughter-in-law of the composer Richard Wagner (1813-1883), had provided assistance here. The company expressed its thanks the following year by supplying a dove – the bird that symbolises divine grace – which was produced artistically from acrylic and provided an added touch to the final scene of the Bayreuth production of Parsifal (Buchholz 2007, 18 and 30-31). 

“After the four-year plan was announced, […] almost all of the acrylic manufactured was used for the important military application of aircraft production. Only production waste and trim were available for processing into consumer goods” (Vaupel 2011, 28). In 1942, supplies to civil processors was discontinued completely following a government ban (Wittig 2007, 58). After all, “demands made by the Ministry of Aviation for 10,000 m² of cast acrylic panelling for aircraft cockpits per month” had to be met (Wittig 2007, 54). But what exactly made the glass substitute so attractive for aircraft production? Alongside resistance to breakage and low weight, it was mainly thermoplasticity, which permitted innovative new designs to be implemented: “Large, shaped panes or domes and hoods made of acrylic were used in the superstructures of airplanes or gliders and gave pilots and passengers an unobstructed view, without intrusive partitioning” (Röhm & Haas 1938, 16). Even the Zeppelin “Hindenburg” was equipped with windows and passenger compartments made from organic glass (Wittig 2007, 40 and Vaupel 2011, 27), as was also highlighted at the “Germany” exhibition held next to the radio tower in Berlin from 18. July to 26. August 1936 (Trommsdorff 1976, 239). Although acrylic had the disadvantage of lower surface hardness, so that it scratched much more easily than silicate glass, “the lower scratch resistance level […] did not play a role in the dust-free atmosphere in which aircraft fly” (Vaupel 2011, 27). In cars, on the other hand, “scratching of the surface by grains of sand was a problem” (Trommsdorff 1976, 238), where the windscreens were concerned at any rate. “It was, however, definitely possible to produce side windows, which were less exposed to the wind, from acrylic” (Vaupel 2011, 27). The company played the problem down: “Scratches are easy to eliminate by polishing” (Röhm & Haas 1938, 12; see also Trommsdorff 1937, 9). In view of this, the Darmstadt company included a polish called “Plexipol” in its product range (Röhm & Haas [no date given], 13). Later on, coatings were applied that brought the hardness level of the surfaces close to those of inorganic glass (Buchholz 2007, 81). Incidentally: the polish was also applied to material that was undamaged, in order to give it “a marvellously glossy finish”, the special acrylic look: “The appeal of this transparent material is increased even more by the low absorption of incident light radiation and the impressive reflection of polished surfaces” (Röhm & Haas 1938, 8).

The business flourished: Röhm & Haas’ annual sales increased dramatically from about 466,000 Reichsmark (RM) in 1934 to a good 23 million RM in 1940, with acrylic accounting for more than two thirds of the total (almost 16.5 million RM (Ackermann 1967, 84). The amount of acrylic produced per day grew from 250 kilograms in 1936 to 4,700 kilograms in 1939 (Edschmid 1957, 61). Production of the monomer, i.e. of methacrylic acid ester, amounted to about 100 tonnes per month in 1939 and increased during the war (Trommsdorff 1976, 231). Some of the monomer was already recovered from 1936 onwards via thermal degradation of acrylic waste (Wittig 2007, 54). In this depolymerisation process, which is also known as “cracking”, the chain molecule structure of the polymer is broken, “although the cost of doing this was no lower than the cost of producing new synthetic material” (Trommsdorff 1976, 241). The process was based on German Imperial Patent 642289 “Process for the production of methacrylic acid esters” (inventor: Dr Paul Weisert), that was granted to Röhm & Haas on 21. July 1935. The following explanation is given in the patent specification: 

“It has been disclosed that high-polymer acrylic acid esters can be depolymerised under the influence of dry distillation. Only di- and trimolecular esters have been obtained in this context, however. It has not been possible up to now to recover the monomer esters. It has been determined that polymer methacrylic acid esters can – in contrast to this – be converted back into monomer esters by heating them above the degradation temperature, i.e. about 250 to 300°. The process can be carried out with polymer methacrylic acid esters or copolymers that contain these esters. The process can be carried out particularly successfully if the polymer is heated with such indifferent inorganic substances as sand, barium sulfate, baryte”. 

(To be continued!)

• Katharina Ackermann (Ed.): Dr Walter H. Bauer and his 67 German Imperial Patents. Achievements and experiences of a German research chemist, compiled on the basis of documents. Jugenheim/Bergstrasse: published by the editor in 1967, 264 pages
• Kai Buchholz (2007): Acrylic. Material in architecture and design. Catalogue for the exhibition at the Mathildenhöhe Institute, Darmstadt, 16. 9. 2007 to 6. 1. 2008. Cologne: Wienand, 151 pages
• Kasimir Edschmid (1957): In memoriam Otto Röhm. On the 50th anniversary of the establishment of Chemische Fabrik Röhm & Haas Darmstadt. Darmstadt: Carl Winter 1957, 75 pages
• Otto Röhm (1936): Organic glass. [Presentation at the meeting of the plastics section of the Association of German Chemists on 9. July 1936, 17.00, during the national conference of German chemists in connection with the 49th annual meeting of the Association of German Chemists in Munich from 7.-11. July 1936] In: Angewandte Chemie, 49th volume, No. 31, P. 591
• Röhm & Haas AG, Darmstadt (n.d.): Acrylic. Processing regulations, 16 pages
• Röhm & Haas AG, Darmstadt (1938): Acrylic – an innovative new material with unusual properties, 27 pages
• Ernst Trommsdorff (1937): The acrylic resins. [Reprint from: “Kunststoffe“, 27th volume] Munich: J. F. Lehmann, 16 pages
• Ernst Trommsdorff: Dr Otto Röhm. Chemist and entrepreneur. Düsseldorf and Vienna: Econ 1976, 294 pages
• Elisabeth Vaupel (2011): Transparent technology thanks to acrylic. About the ideology of transparent models in the Thirties. In: Kultur & Technik, 35th volume, No. 2, pages 26-31; online: www.deutsches-museum.de/uploads/pics/26-31Vaupel_Plexiglas_RZ_web.pdf
• Eva Wittig: Shaping the future for 100 years. Röhm GmbH from 1907 to 2007. Munich: Peschke 2007, 112 pages