Nits Tates Atnt “6Iv

l". .. assess nits tates atnt “6iv. i5 Patented Aug‘. 21, 1952 1 2 necessary to convert the normally liquid or solid mono 3,950,390 mers into solid polymers. This is particularly true when PHOTQPOLYMEREZATIQN 0F VENYL MONOMERS the silver compound itself is capable of further oxida BY MEANS OF SILVER CUMPOUNDS AS CATA~ LYSTS PROMGTED BY AWPHOTERIC NIETAL tion, i.e., silver nitrite and/ or the amphoteric metal oxide OXEES is utilized with another compound of the same metal which Steven Levinos, Vestal, and Fritz W. H. Mueller, Bing is capable of ready oxidation, such as, for example, Zinc hamton, N.Y., assignors to General Aniline & Film sul?te. Corporation, New York, N.Y., a corporation of Dela The characteristics of the radiation-sensitive silver com ware pounds used as catalysts are generic to such a class and No Drawing. Filed Get. 6, 1958, Ser. No. 765,275 it is not restricted to a few members thereof. Silver com 25 Claims. (Cl. 96-35) pounds which are very active oxidation agents, such as, The present invention pertains to the formation of for example, silver perchlorate, are excluded since these solid polymers by photopolymerization of normally liquid react explosively with ethylenically unsaturable mono or solid ethylenically unsaturated monomers while em mers even in the dark and cause such compounds to ploying a radiation-sensitive silver compound as the cata undergo oxidation rather than polymerization. Similarly, lyst and a metal oxide capable of forming amphoteric silver compounds which decompose when stored in dark bases as a promoter for the catalyst. ness are not contemplated for use. It has been proposed to photopolymerize ethylenically ‘Examples of silver compounds possessing the necessary unsaturated monomers in the presence of water while prerequisities are: silver acetate, silver acetylide, silver utilizing a radiation-sensitive silver compound as the cata ortho-arsenate, silver ortho-arsenite, silver benzoate, silver lyst by irradiating the monomer and silver compound with tetraborate, silver bromate, silver bromide, silver car rays having a wave length of from 10-1 to 1O—10 centi bonate, silver chloride, silver chromate, silver citrate, meters. Polymerization in this fashion to yield solid silver ferrocyanide silver ?uoride, silver iodide, silver polymers may be carried out in bulk or imagewise in lactate, silver ?uosilicate, silver cyanide, silver thiocyanate, coatings containing the monomer and catalyst. It was 25 silver laurate, silver levulinate, silver phenol-sulfonate, later determined that such photopolymerization could silver ortho~phosphate, silver myristate, silver nitrate, be more efficiently controlled when employing the silver silver nitrite, silver picrate, silver nitro-prusside, silver salts in the form of light-sensitive photographic emulsions selenate, silver selenide, silver potassium cyanide, silver of various types. Thus, by use of such emulsions which oxalate, silver oxide, silver ammonium hydroxide (am are amenable to sensitization by optical and chemical sen moniacal silver oxide), silver palmitate, silver propionate, sitizers employed in the photographic industry, it was silver salicylate, silver sul?de, silver acridine, silver hy possible to make the monomeric materials selectively ponitrite, silver azide, silver tellurate, silver sul?te, silver reactive to radiations of various wave lengths. Of par thionate, silver sulfamate, silver stearate, silver sulfate, ticular importance is the fact that in both of the outlined silver tartrate, silver thiosulfate, silver tungstate, silver procedures resorting to silver compounds for catalyzing 35 molybdate, silver iridate, silver formate, silver malonate, the photopolymerization, the reaction could be effected silver succinate, silver glutarate, silver adipate, silver al with visible light, contrary to the usual experience in this buminates, silver caseinates, addition compounds of ben ?eld. zidine and silver nitrate, addition compounds of silver ‘We have now realized a further improvement in the nitrate and quinoline, silver vanadate, or the silver salts photopolymerization of ethylenically unsaturated mono 40 of U.S.P. 2,193,574 such as the silver salt of p-nitro mers (solid or liquid) with silver compound catalysts in oxanilic acid, the silver salt of 6,6'-dinitro-ortho-tolidine, that we have discovered that the catalytic activity of the dioxamic acid, the silver salt of benzene sul?nic acid, the silver compounds may be greatly promoted or enhanced silver salts of U.S.P. 2,066,582, silver salts of the amino by the use therewith of small amounts of metal oxides acids such as those described in U.S.P. 2,164,687 and capable of forming ‘amphoteric bases. U.S.P. 2,454,011, i.e., silver lysalbinate, silver gelatose, An additional and very important ?nding is that our etc. catalytic system becomes even more effective when there ‘Only catalytic amounts of the silver compound are are employed small amounts of optical sensitizing dyes needed. This means that the ‘silver compound will be such as erythrosin, eosin, pinacyanol, l,l'-diethyl-2,2' employed in an amount which is exceedingly small when cyanine iodide and similar cyanine sensitizing dyes dis measured against the quantity of monomer. We have ef closed in Chapter 7 of “Photography, Its Materials and fectively used a silver compound (silver sul?te) in an Processes,” by C. D. Neblette (Fifth Edition), published amount by weight as low as l/ggopoo of the weight of the by D. Von Nostrand Company, Inc., New York City. monomer. Greater amounts of the silver catalyst by weight may be employed but are generally found to be The direct formation of solid polymers by irradiation, 55 with radiations ranging in wave length from 1()—1 to unnecessary. For example, we have obtained excellent 10*“, of ethylenically unsaturated monomers which are results with amounts of silver compound ranging up to normally liquid or solid (at room temperature) in the 10% by weight of the monomer. resence of a radiation-sensitive silver compound as a The amphoteric metal oxides which we have found to catalyst and a small amount of an amphoteric metal be active promoters for the silver compounds are zinc 60 oxide ‘as a promoter for the catalyst with or without oxide, titanium dioxide, zirconium dioxide and silicon di~ optical sensitizing dyes constitutes the purposes and objects oxide. These oxides are all available on the open market of our invention. and may be obtained in various physical forms. For ex The particular mechanism by which photopolymeriza ample, silicon dioxide is sold by several companies in the tion is achieved by use of silver compound catalysts has form of a colloidal dispersion or in the form of a ?ne 65 not been ascertained and is not self-evident. It is pos powder which may readily be dispersed. There is, there sible that the photopolymerization is due to the presence fore, no d?iculty in obtaining these oxides for use in our of free radicals produced during the decomposition of the procedure. radiation-sensitive silver compounds. On the other hand, Our experiments have indicated that, while the silver compounds alone will effect photopolymerization of the impact on the reaction of the metal oxides is un 70 known. The fact is, however, that when the amphoteric ethylenically unsaturated monomers, the rate of polym metal oxides are present, they materially reduce the time erization is greatly enhanced when the silver compound is 3,050,390 3 A used with an oxide of the stated class. For example, a liquid at room temperature) as toluene, acetone, metha mixture of acrylamide with a cross-linking agent such nol, butylacetate, ethylmethylketone, benzyl alcohol and as N,N’-methylene-bis-acrylamide was photopolymerized the like. ' in the presence of silver nitrate in a period of about 11 ‘It is understood, however, that where an organic solvent minutes. When to the same reaction mixture there was system is employed, provision must be made for the pres added a small amount of zinc oxide, photopolymeriza ence in the system of a small quantity of water, say about tion under the same conditions ensued in 7 minutes. In .1 to 5% by weight. The water may be added as such or each case, solid high molecular weight products were may be supplied by incorporating in the reaction mixture obtained. a humectant such as ethylene glycol, glycerine or the like. The fact that the amphoteric metal oxides reduce the 1O When these substances are present, say in an amount of time necessary for the silver compounds to effect photo a few percent by weight of the mixture, they absorb suffi polymerization spells out a synergistic effect in the use cient water from the atmosphere to permit photopolym of the catalyst on the one hand and the promoter therefor erization to proceed. on the other hand. The effect, as previously explained, Dispersions may also be used in effecting the photo is not evident and appears to be impossible of ascertain 15 polymerization as previously indicated. These may be ment. formed by dispersing a water insoluble monomer in The quantity of amphoteric metal oxide employed Water by means of a dispersing agent and dispersing the Whether polymerization be e?ected in bulk or imagewise silver compound and promoter in the resulting suspension is quite small, ranging in an amount from about .01 to 1% or dispersion. Suitable dispersing agents are, for ex by weight of the monomer. Larger amounts may, of 20 ample, long chain fatty acid sarcosides or taurides, i.e., course, be employed but no improvement in results

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