2,951,834 United States Patent Office Patented Sept. 6, 1960 1. 2 The rate of reaction may be controlled by external 2,951,834 cooling of the reaction mixture or by allowing solvent to evaporate in a controlled manner, for example by manip MXED ANHYDRDES AND THEIR USE AS CATA ulation of the pressure, usually to maintain a tempera LYSTS FOR THE POLYMERISATION OF ETH. ture of -80° to -20° C., preferably below -40° C. YLENICALLY UNSATURATED COMPOUNDS and as low as -110° C. if desired. Gerald Scott, Manchester, England, assignor to Imperial The products of the reaction between hyponitrous acid Chemical Industries Limited, London, England, a cor or a metal hyponitrite and the haloformic esters are rela poration of Great Britain tively unstable materials and products of different stabil 10 ity may be obtained according to the conditions under No Drawing. Filed Mar. 25, 1958, Ser. No. 723,645 which the reaction is carried out. The less stable prod Claims priority, application Great Britain Apr. 1, 1957 lucts are preferred for use as catalysts, and their forma tion is favoured by the use of short reaction times which 13 Claims. (C. 260-94.9) in turn are favoured by small particle size of starting 5 materials and the presence of an excess of hyponitrous This invention relates to mixed anhydrides and to their acid or salt. use as catalysts for the polymerisation of ethylenically un When the reaction between a haloformic ester and a saturated compounds. metallic hyponitrite is finished the metal halide co-product According to the invention there are provided mixed may readily be removed, for example by filtration. Much anhydrides of hyponitrous acid and at least one organic 20 of the desired mixed anhydride may remain adsorbed on monoester of carbonic acid. the insoluble halide and it is desirable to wash the residue The mixed anhydrides of this invention have the gen thoroughly. By this means the total yield of mixed an eral formula hydride may be more than doubled in certain cases. If a relatively non-polar medium is used in the reaction it A & b 25 may be desirable to elute the residue with a more polar where R and R' stand for alkyl, cycloalkyl, heterocyclo solvent. The solution of the mixed anhydride so obtained alkyl, aralkyl, allyl or aryl groups, which groups may be is generally used as such in the polymerisation of ethyl substituted or unsaturated. The groups R and R may emically unsaturated compounds; however, the mixed an be substituted, for example, by halogens, alkoxy, cyano, hydride may be isolated from the solution, for example 30 by evaporation of the solvent at low temperature or by or ester groups, or by radicals containing one or more crystallisation at low temperature. The pure mixed an further alkoxyformyl hyponitrite residues, in which case hydrides may be dangerously unstable and it is for this the product is polymeric. In all cases, R and R' may be reason that their isolation is usually avoided. the same or different. Examples of the mixed anhydrides of this invention The invention also includes a process for the produc 35 are the mixed anhydrides of hyponitrous acid and meth tion of the mixed anhydrides that comprises interacting oxy, ethoxy, propoxy, isopropoxy, n-butoxy, sec-butoxy, at a temperature.below 0° C. hyponitrous acid or a salt tert-butoxy, amyloxy, allyloxy, benzyloxy, eyelohexanoxy, thereof with at least one haloformic ester of the formula tetrahydrofurfuranoxy, 3.5.5 trimethylhexanoxy, 2-ethyl Hall-C-OR hexanoxy, p-tolyloxy, o-chlorophenyloxy, 1-carbethoxy 40 propan-2-oxy, B-methoxyethoxy and B-chloroethoxy for wherein R has the significance hereinbefore described, mic acids. preferably the chloroformic ester. Salts of hyponitrous The mixed anhydrides, which are catalytically active, acid that may be used include the silver, lead, thallium, decompose at appreciable rates with evolution of gas at copper, potassium or ammonium salts. The silver salt temperatures as low as -40 C. Pure catalytically ac is generally preferred because it is readily prepared in a tive mixed anhydrides yield approximately 50% CO and pure state and is highly reactive. When hyponitrous 45 50% N2 in the gaseous decomposition products. Small acid is used it may be convenient to generate it from an amounts of nitrous oxide are often found also and the inorganic hyponitrite by means of a strong acid such as amounts may be considerable when impure silver hypo hydrogen chloride. Titrite or peroxydized solvents have been used in the The reaction between the hyponitrous acid or salt and preparation. Products which yield much nitrous oxide the haloformic ester may be performed in a solvent me 50 are less desirable as catalysts. dium for the haloformic ester and the mixed anhydride; The mixed anhydrides are valuable catalysts for the for example, ketones, ethers, esters, amides, nitriles, polymerisation and copolymerisation of ethylenically un aliphatic nitro compounds, halogenated hydrocarbons, pe saturated compounds, including dienes; this use of the troleum hydrocarbons or aromatic hydrocarbons may be mixed anhydrides is a further feature of our invention. used. It is essential that the solvent should remain liquid 55 The mixed anhydrides are particularly useful for the (at the low temperature of reaction. The solvent may be polymerisation of ethylene to give solid polymers attem gaseous at room temperature, but may be liquid at the peratures as low as -40° C. and pressures above 100 reaction temperature with or without the application of a atmospheres, preferably between 1,000 and 3,000 atmos moderate pressure. Suitable solvents include acetone, pheres, and to give high rates of polymerisation at room nitroethane, ethylene glycol diether ether, acetonitrile, di 60 temperature. If provision is made for the control of fast ethyl oxalate, and dimethyl ether; acetone is a particu reactions and removal of large quantities of heat as in a larly satisfactory solvent. The reaction is considerably continuous process, very high rates of polymerisation assisted by the presence of a tertiary base, especially pyri may be obtained at temperatures as high as 180° C. dine, or salts thereof. The tertiary base or its salt is The pressure preferred depends to some extent on the best used in quantities of 10-1,000 p.p.m. of the amount 65 desired temperature of operation and is chosen so that of haloformic ester when the latter is reacted directly the gas density always exceeds 0.21 gm./cc. The use of the with an inorganic hyponitrite, although larger quantities mixed anhydride at low temperatures is especially valuable may be used if desired. When the haloformic ester is because branching of the polymer chains decreases with reacted with hyponitrous acid, it is desirable to have decreasing polymerisation temperatures, and the more present an amount of base chemically equivalent to the 70 linear polymers obtained at low temperatures are stiffer amount of reactive halogen present in the system. and of higher melting point and density than those pro 2,951,834 3 - 4. ducted at high temperatures. Low temperature processes 1. The yield of ethoxyformyl hyponitrite is 7% and all are capable of giving polymers of density exceeding 0.95 of this decomposes between -20 and -30 C. if desired. The melt viscosity and molecular weight of the polymers may be modified to any desired level for the Example 3 purposes of fabrication or strength by choice of reaction To a suspension of 27.6 parts of silver hyponitrite in pressure and by the addition to the polymerisation reac 108 parts of acetone at -60° C. is added a solution of 7.3 tion vessel of chain-transfer agents such as hydrogen, parts of hydrogen chloride in 92 parts of acetone. To the carbon-tetrachloride or other chlorinated hydrocarbons, solution of hyponitrous acid thus formed at - 60° C. are lower alkanes or cycloalkanes, ethers and esters. Inert added 19 parts of ethyl chloroformate. The mixture is diluents may also be present. 10 then stirred at -30° C. for two hours and the suspension Other ethylenically unsaturated compounds that may is filtered by the method used in Example 1. Two-thirds advantageously be polymerised and copolymerised among of the gaseous decomposition products corresponding themselves or with ethylene by general methods described roughly to a 5% yield of ethoxyformyl hyponitrite are in the prior art or used hitherto, but with the use of the released between -30 C, and 0° C. mixed anhydrides of this invention as catalysts, include, 5 for example: styrene, methyl methacrylate, vinyl acetate, Example 4 vinyl chloride, isoprene, butadiene, acrylonitrile, fluoro The process of Example 3 is repeated except that 16 ethylenes, propylene, N-vinylphthalimide, methacrylam parts of pyridine are added after the addition of the ide, vinylidene chloride, chloroprene, fluoroprene, N ethyl chloroformate, and the whole mixture is then stirred vinylcarbazole, N-vinyl pyrollidone, acenaphthene, maleic 20 at -30° C. for only one hour before the suspension is anhydride, indene, chlorinated styrenes and diallyl fuma filtered by the method used in Example 1. The yield of rate. The polymerisation of these monomers may be ethoxyformyl hyponitrite is 35% and the product decom carried out at normal or elevated or reduced pressures or poses between -30 and -30° C. temperatures and in the presence or absence of inert sol vents or other diluents such as water or gaseous or liquid 25 Examples 5, 6 and 7 hydrocarbons. In general, the only change introduced by Example 4 is repeated but with the differences indicated the use of the new catalysts in the polymerisation proc below: esses of the prior art is that for a given polymerisation temperature the rate of polymerisation is surprisingly in Example Chloroform- Parts - Time, Yield, ate o C.