Chemically speaking, it is merely one step from plastics made out of polymethacrylate (PMA) to Perspex, i.e. polymethyl methacrylate (PMMA), production of which began at Röhm & Haas AG in 1928 (Hölscher 1972, 121). In contrast to acrylic acid, methacrylic acid has a methyl group (CH3) and/or is derived from it “by replacing 1 hydrogen atom in it by 1 methyl atom” (Frankland/Duppa 1865, 13; see also Trommsdorff 1976, 224). The small difference is important for the properties of the polymers in question, for example their solubility, flexibility and hardness level:
“In the course of his research into acrylic acid synthesis, Walter Bauer came across methacrylates as the next homologues of acrylates as early as 1919, but did not investigate them any further. It was not until eight years later, when the material properties of acrylates had largely been determined that he pushed for examination of methacrylates by way of comparison. Otto Röhm initially deferred this work in favour of LUGLAS. Two years later, Walter Bauer continued his research work with the aim of examining the suitability of methacrylates for laminated glass. In this context, he made a systematic investigation of the properties of the most important homologues of methacrylates, with the primary focus on methyl methacrylate (MMA) and polymerisation of it. It turned out that polymethyl methacrylate (PMMA) – in contrast to the acrylates investigated beforehand (polyacrylic acid methyl ester and its homologues) – was a hard, clear material.” (Wittig 2007, 35-36)
The advantage was obvious: “Where acrylates were too soft or too tacky and/or swelled badly, it was possible to compensate for such difficulties with the help of methacrylates” (Wittig 2007, 43), because “the polymer methyl ester” represents “the hardest polymer with the highest softening point” (Trommsdorff 1976, 232).
“Polymers of methacrylic acid and its compounds, such as esters, salts, or methacrylic acid amide are possible options for use as plastics” is what it says in the specification of the patent “Plastic” (DRP 656642 of 27. October 1928, inventor: Dr Walter Bauer) granted to Röhm & Haas AG. Moulded products or elastic films, e.g. membranes for linings or covers, as well as lacquers and resins are given as examples of applications for polymerised methacrylic acid ester. The potential to be an organic substitute for glass is only mentioned here on the side:
“It has already been suggested that polymerised itaconic acid ester is used as a plastic and, in particular, as a glass substitute. This invention relates exclusively to use of the functional derivatives of the homologues of acrylic acid. A comparison between the properties of polymers made in accordance with the invention and polyitaconic acid ester shows that there are not only identical properties like crystal-clear transparency but also substantial superiority in various directions. Polyitaconic acid ester is comparatively brittle, whereas polymethacrylic acid esters are, for example, comparatively tough, a property that is of considerable or even – in certain cases – crucial importance for many plastics. Polyitaconic acid esters change to a soft, more or less molten state at temperatures of as low as about 40 to 50°. Polymethacrylic acid esters, on the other hand, can be heated up to temperatures of 100° or more without melting or being changed to their disadvantage.”