1933, German chemist Otto Ruff (1871-kloc-0/939) and others made hydrofluoric acid (HF) by reacting fluorite (CaF2) with sulfuric acid, and then reacted with chloroform (CHCl3) to obtain monochlorodifluoromethane (CHClF2).
Calcium fluoride+sulfuric acid/calcium sulfate +2HF (hydrofluoric acid)
Chcl3+2hf ═ chclf2+2hc monochlorodifluoromethane is a gas with a boiling point of -40.8℃, which is easy to liquefy and can be used as a refrigerant. However, it is decomposed by heat, for example, it is decomposed into tetrafluoroethylene (CF2=CF2) at 700℃ by passing it through a platinum metal tube.
2C HCl F2 ═ CF2 = CF2+2HCl tetrafluoroethylene is the product that four hydrogen atoms in ethylene (C2H4) molecule are completely replaced by fluorine atoms. Tetrafluoroethylene is a gas at room temperature, and its boiling point is lower than that of chlorodifluoromethane, so it must be kept frozen, in a steel bottle and in a box frozen with dry ice (solid carbon dioxide).
1938 Plum Kett, an American doctor of chemistry, studied tetrafluoroethylene, made a little, and put it in a cylinder in the freezer.
One day, with the help of assistant J. Rebok, Plumkate took out a small cylinder filled with 2 pounds (1 pound is about 0.45 kilograms) of tetrafluoroethylene from the freezer, put the cylinder on the scale, let tetrafluoroethylene gas flow out of the cylinder, and then let tetrafluoroethylene enter the chemical reaction system he studied through the flowmeter.
Shortly after the start of the experiment, Rehbock observed from the flowmeter that the tetrafluoroethylene gas flow from the cylinder had stopped, and Plum Kate immediately checked the quality displayed on the balance. He found that the weight of the whole cylinder did not decrease a lot, that is to say, 2 pounds of tetrafluoroethylene in the cylinder did not flow out in large quantities, and a considerable amount of tetrafluoroethylene remained in the cylinder. This surprised Maykate and his assistant.
In order to find out the problems in the cylinder, Mei Kate had to open all the valves in the cylinder and dredge the channels of the valves with filaments so as not to be blocked.
. He formulated the synthesis method and production process of PTFE, delivered it to DuPont Company of the United States and put it into production. It was put into the market under the trade name teflon in 1945.
Li Wen Chemical discovery and invention. Beijing: Science Popularization Press, 1985.
Polytetrafluoroethylene is a kind of plastic with good performance, which has four main characteristics:
(1) is the earliest discovered and the largest production of high-temperature and low-temperature resistant plastics. It can be used for a long time at 250℃ and for a short time at 300℃, which is higher than that of polyethylene 170℃.
(2) Excellent chemical resistance, no corrosion in strong acid and alkali, and insoluble in any solvent even when heated.
(3) Low friction coefficient. Its friction coefficient is half less than that of two kinds of polished stainless steel, and its wear is only 1% of that of stainless steel.
(4) Excellent dielectric properties. The film with a thickness of 0.025 mm can withstand 500 volts, which is twice the insulation strength of nylon.
Therefore, PTFE has won the reputation of "king of plastics", which is widely used in manufacturing gaskets and hoses for cryogenic liquid transportation pipelines, fire-retardant coatings for space flight to the moon, bearing covers, bearing bushes, oil-free lubricated pistons, high-temperature liquid pipelines in petrochemical plants, pipeline sealing materials, anti-corrosion linings and so on.
Teflon is also a material for making non-stick pans in family kitchens.
Almost at the same time, new excellent plastics appeared at the same time as PTFE. They are different trade names of the same product in different countries and companies. They are plexiglass (British Imperial Chemical Industry Company), oroglas (USA), plexiglas (Germany), cryace (Japan), lucite (DuPont) and verdril (Italy). Among them, plexiglass (Pespex) appeared earliest, about 1935. The chemical name of this product is polymethyl methacrylate.
Ester is a compound produced by the interaction of alcohol and acid in organic compounds, just like alkali in inorganic compounds loses water to produce salt.
The molecular structural formula of acrylic acid is:
The molecular structural formula of methyl methacrylate is:
Judging from their molecular structure, they have double bonds and may polymerize.
Therefore, as early as 1888, Swiss chemist G.W.A.Kahlbaum made an unbreakable beer glass from the polymerization product of methyl methacrylate, and obtained a patent in 19 12. Almost at the same time, German chemist R. Fittig (1835-1910) found that methacrylic acid and some of its derivatives were easy to polymerize. To 1927, German chemist Rum (O.R.? Hm) and others produced a small amount of polymethacrylate and put it on the market under the trade names acryloid and plexigum. Around 1930, R.Hill, a chemist of British Imperial Chemical Industry Company, and W.Bauer, a chemist of Germany, independently made polymethyl methacrylate, which is a hard and transparent polymer and can be used as a window glass of aircraft. At the same time, during the period of 1929- 1930, Canadian chemist W. Chalmers discovered that the polymer of ethyl methacrylate and methacrylonitrile was a hard and transparent substance, and obtained patents in Canada and the United States successively. After research, chemists from Imperial Chemical Industry Company in Britain determined that the polymer of methyl methacrylate has a higher softening temperature than that of ethyl methacrylate. By 1932, J.W.C Crawford, a chemist of Imperial Chemical Industry Company, had developed a low-cost production method of monomer methyl methacrylate. The raw materials are acetone ((CH3)2CO), hydrocyanic acid (HCN) and methanol (CHCH). The whole chemical reaction process is represented by the following chemical reaction formula:
Polymerization is carried out under the influence of catalyst. In production, if you want to make a flaky glass-like material, it needs to be carried out at 70℃ in the presence of a catalyst until a colorless and viscous syrup solution is formed. Pour the syrup-like solution into the mold or put it between two pieces of smooth glass, put the mold into an oven at 50℃, take out the mold after the polymerization reaction is completed, and open it after cooling to obtain pieces of transparent plexiglass.
If you want to make molding or casting materials, the polymerization reaction must be carried out in an autoclave, and the monomer will be diluted into emulsion with water. The polymer thus produced is suspended in water and then gradually sinks to form a fine-grained precipitate. Fig. 40- 1 vividly depicts its polymerization reaction. The larger black ball represents carbon atoms, the gray ball represents oxygen atoms, and the smaller white ball represents hydrogen atoms.
This plexiglass has the following characteristics:
(1) is highly transparent, with a light transmittance of 92%, which is higher than that of silicate inorganic glass. It can completely transmit ultraviolet rays, inorganic glass can only transmit 0.6%, while plexiglass can transmit 73% ultraviolet rays.
(2) High mechanical strength, with tensile strength of 600 ~ 750kg/cm2 and impact strength of 12 ~ 13kg? Cm/cm2 is 7~ 18 times higher than inorganic glass. There will be no cracks and acute angles when penetrating with nails or bullets.
(3) Light weight, with a relative density of 1. 18, which is only 1/2 of inorganic glass and 43% of light metal aluminum.
(4) It is resistant to atmospheric aging, and the light transmittance only decreases by 65438 0% after being placed outdoors for 5 years.
(5) It is easy to form and can be mechanically cut, chipped, turned and cut. It can also be molded by heating such as blow molding, injection and extrusion, and can be self-adhered after being dissolved in solvents such as acetone and chloroform (CHCl3).
Therefore, this plexiglass is completely suitable for making aviation glass, and can also be used to make unbreakable magnifying glasses, dials and surface glasses of watches and clocks, transparent utensils, buttons, brooches and so on. (Figure 40-2). It is also the material for making false teeth.