MXPA96004156A - Process for the preparation of hydrogen rubber - Google Patents

Abstract

The present invention relates to a process for the preparation of a latex of a hydrogenated elastomeric polymer comprising: 1) combining an unsaturated polymer in the form of a latex with a) an oxidant selected from the group consisting of oxygen, air and hydroperoxide b) a reducing agent selected from hydrazine and hydrates thereof, and c) a metal ion activator, 2) heating the mixture at a temperature of 0 ° C. to the reflux temperature of the reaction mixture; ) treating the mixture with ozone in an amount and under conditions which are sufficient for the ozone to react with the residual polymer unsaturation to form an ozonized latex of an elastomeric polymer having at least one final aldehyde end group; the latex ozonized with hydroxylamine in an amount and under conditions which are sufficient to convert the final aldehyde groups of the elastomeric polymer into the oxime end groups in order to form an oxime polymer latex

Description

"PROCESS FOR THE PREPARATION OF HYDROGENATED RUBBER" BACKGROUND OF THE INVENTION As revealed by the article by Parker and others in Rubber Chem. & Tech., Volume 65, 245 (1992), NBR latexes that are converted to hydrogenated NBR latexes by the method disclosed in US Patent Number 4,452,950 are likely to have a secondary reaction of undefined crosslinking occur simultaneously with the reduction desired of the double bonds. This crosslinking reaction produces hydrogenated saturated "gelled" or "cross-linked" NBR latex particles. For many latex applications, this crosslinking can have a beneficial effect. For example, latex molded films of this material can form continuous rubber coatings with good tensile, elongation and elastic recovery properties. Unfortunately, however, when the highly crosslinked latexes are coagulated by common techniques known in the art, the resulting dried rubber mass is not capable of processing and flowing to any significant degree due to its macroscopic three-dimensional cross-linked structure. The material essentially has an "infinite" molecular weight in this form and can not be processed by conventional rubber equipment. A possible solution to this dilemma was disclosed in U.S. Patent No. 5,039,737 whereby the crosslinked "hydrogenated" NBR latex prepared by US Pat. No. 4,452,950 is first treated with ozone to dissociate the residual non-reduced double bonds. This treatment resulted in the reduction of the molecular weight of the rubber with simultaneous generation of both aldehyde end groups and carboc acid terminals at the dissociation sites. Unfortunately, even when the originally cross-linked hydrogenated NBR rubber can be made soluble in a good solvent for hydrogenated NBR (e.g., chloroform), if it is immediately coagulated from the latex and redissolved, upon drying, the cross-linked soluble rubber is again It becomes useless. This problem could however be overcome, as disclosed in U.S. Patent No. 5,039,737 by reducing the terminal aldehyde groups in the polymer, using the strong and relatively expensive reducing agent ... sodium borohydride, in an ethanol solution. Supposedly, the aldehyde groups are converted to terminal polymeric alcohol groups (after the hydrolysis of the borate intermediates) which have no tendency to re-crosslink since the resulting polymer has been reported to remain soluble. Unfortunately, this method of using sodium borohydride to obtain a processable hydrogenated NBR rubber is troublesome, costly, uses alcohol solvents and releases hazardous hydrogen gas during the process. In contrast to the process described in U.S. Patent No. 4,452,950 and in the article by Rubber Chem. & Tech., Volume 65, 245 (1992), commercial hydrogenated NBR dry rubber is prepared by a completely different technique. In this method, the dried NBR rubber is first crushed into particles and then dissolved in a solvent. A noble metal catalyst is then added to the resulting cement. The mixture is then subjected to hydrogen pressure at elevated temperatures to effect the reduction of the double bonds. The expensive solvent and catalyst are then removed in a series of steps resulting in the hydrogenated NBR rubber having essentially the same molecular weight and structure as the original NBR. Therefore, if the original NBR was processable, the resulting hydrogenated NBR will be more likely to be processable as well. Even though this method easily produces the processable hydrogenated NBR, it suffers from being an extremely expensive and complicated process. Dangerous hydrogen gas is used and the solvents and valuable metal catalysts are unable to recover completely.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for the preparation of a hydrogenated elastomeric polymer latex comprising: (1) combining an unsaturated polymer in the form of a latex with (a) an antioxidant selected from the group consisting of oxygen, air and hydroperoxide; (b) a reducing agent that is selected from hydrazine and hydrates thereof; and (c) a metal ion activator; (2) heating the mixture at a temperature of 0 ° C to the reflux temperature of the reaction mixture; (3) treating the mixture with ozone in an amount and under conditions which are sufficient for the ozone to react with the unsaturation of the residual polymer in order to form an ozonized latex of an elastomeric polymer having at least one aldehyde end group; (4) treating the ozonized latex with hydroxylamine in an amount and under conditions which are sufficient to convert the aldehyde end groups of the elastomeric polymer into oxime end groups to form an approximate polymer latex. Also disclosed is a novel oximized polymer latex which is prepared in accordance with the process of the present invention. Also disclosed is a novel dry rubber that is derived from the approximate polymer latex prepared in accordance with the present invention. The process of the present invention begins with an unsaturated polymer in the form of latex. The unsaturated polymers useful in this invention are composed of from 5 percent to 100 percent by weight of a conjugated diene monomer unit and from 95 percent to 0 percent by weight of an ethylenically unsaturated monomer unit. Specific examples of the conjugated diene monomer are 1,3-butadiene, 2,3-dimethylbutadiene, isoprene and 1,3-pentadiene, specific examples of the ethylenically unsaturated monomer include unsaturated nitriles such as acrylonitrile and methacrylonitrile, monovinyl aromatic hydrocarbons such as styrene (o-, m- and p-) alkylstyrenes, divinyl aromatic hydrocarbons such as divinylbenzene, dialkenyl aromatics, such as diisopropenylbenzene, unsaturated carboxylic acids and the esters thereof such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and methyl methacrylate; vinylpyridine; vinylidene chloride and vinyl esters such as vinyl acetate. The unsaturated polymer can be one that is prepared by any method of preparation such as emulsion polymerization, solution polymerization or volumetric polymerization. Specific examples of the conjugated diene polymer include polyisoprene, polybutadiene, a styrene / butadiene copolymer (random or block), an acrylonitrile / butadiene copolymer (random or blocked), a butadiene / isoprene copolymer and a copolymer of isoprene-isobutylene. The preferred polymer is an acrylonitrile / butadiene copolymer (NBR). It is preferred that the polymer be prepared in an aqueous emulsion polymerization without prior coagulation or use of organic solvents. If the polymer to be hydrogenated is not in the form of a latex, then by known techniques, the polymer should be placed in the form of a latex. Conventional cold or hot emulsion recipes can be used to prepare the unsaturated polymer in latex form. Conventional ionic surfactants, known in the art including sulfonate detergents and carboxylate soaps are useful in the present invention. The level of the ionic surfactant is calculated based on the total weight of the charged monomers and ranges from 1 part to 30 parts by weight of the ionic surfactant per 100 parts by weight of the monomer (phm) with an amount of 1 to 15 phm being preferred. and an amount of 2 to 10 phm being especially preferred. The process of the present invention does not depend on any initiator, activator, reducing agent, complexing agent, stabilizer, oxygen combination substances, emulsifier, dispersing agent, modifier and specific similar substances that are used to prepare the unsaturated polymer in the form of latex. The unsaturated polymer in the form of latex is prepared by polymerizations in which the metal compounds of the redox system are completely formed in a complex (or almost completely); that is, that the polymerization is carried out in the presence of a sufficient amount of the complexing agent so that at least 90 percent of the metal compound is caused to react therewith to form a water soluble complex compound. These complexing agents therefore constitute part of the redox system and are already present at the beginning of the polymerization. A very suitable complexing agent, for example, is a mixture of 90 percent tetrasodium salt of ethylene diaminotetraacetic acid and 10 percent of a monosodium salt of N, N-di (alpha-hydroxyethyl) glycine. Another suitable complexing agent is the disodium salt of ethylene diaminotetraacetic acid. Free radical initiators known in the art are useful for preparing the polymer in the form of latex. For example, persulfate systems and azonitrile systems are conventionally used in hot emulsion recipes. Examples of free radical initiators conventionally used in cold emulsion recipes include combinations of chelated iron salts, formaldehyde-sodium sulfoxylate, organic hydroperoxides. Representative of the organic hydroperoxides are cumene hydroperoxide, paramentane hydroperoxide, diisopropylbenzene hydroperoxide, pinene hydroperoxide and tertiary butyl hydroperoxide. The redox recipes applied in the polymerization include an initiator (hydroperoxide) and an activator, which as a general rule consists of several components (among which is the metal compound). These recipes are often varied so that other amounts of initiator and / or activator are applied.

The values specified can then be designated as at a level of 100 percent or at a level of 100/100, with the desired modifications expressed in percentages thereof, for example 50 percent level of initiator / activator level = 50/50. Activators usually comprise a heavy metal (numbers 23 to 29 of the Periodic Table), water-soluble salts, such as ferrous sulfate, cobalt chloride, cuprous chloride, nickel sulfate, etc. In certain cases it may be convenient to polymerize at this initiator level that, upon reaching the desired conversion, the initiator is almost consumed. For example, this can be done by selecting a low ratio between the level of the initiator and the level of the activator, for example between 0.4 to 0.6. The temperature of the emulsion polymerization can vary from 0 ° C to 100 ° C. If the hot polymerization recipe is used, the temperature of the polymerization usually ranges from about 40 ° C to about 100 ° C. Preferably, the temperature of the hot polymerization ranges from about 45 ° C to about 80 ° C, with a scale from about 50 ° C to about 70 ° C being particularly preferred. Hot polymerization is usually carried out until monomer conversion varies from 80 percent to 100 percent. The temperature of the cold polymerization usually varies from about 0 ° C to 25 ° C. Preferably, the temperature of the cold polymerization ranges from about 5 ° C to 20 ° C with a scale of about 5 ° C to about 15 ° C being particularly preferred. Cold polymerization is usually carried out until the monomer conversion varies from about 65 percent to 100 percent. In addition, a chain transfer agent is generally used in order to avoid excessive gel formation to control the average molecular weight. Conventional retention agents can be used in amounts ranging generally from about 0.01 to 2.0 phm (parts per hundred parts of the monomer). The manner by which the retention agent is added is in accordance with the conventional techniques used in rubber polymerization processes. Polymerizable antidegradant agents may also be present during the emulsion polymerization. For example, U.S. Patent Nos. 3,658,789 and 3,767,628 incorporated herein by reference disclose various amide and imide antidegradation agents that are copolymerized. with the conventional monomers in a free radical polymerization. The weight average molecular weight of the polymer latex can vary widely. Generally, the weight average molecular weight ranges from about 10,000 to about 2,000,000. Preferably, the molecular weight will vary from about 30,000 to 500,000. Particularly preferably, weight average molecular weights of between 30,000 and 200,000 are used. The polymer latex form can be hydrogenated as is. The concentration of the latex can vary from 1 percent to 70 percent by weight, preferably from 20 percent to 50 percent by weight. The dihydrate hydrogenation reaction is preferably carried out in an open container. The reaction temperature is from 0 ° C to 300 ° C, preferably from 40 ° C to 80 ° C. Pressure vessels are not required or preferred, however, pressures can vary from atmospheric pressure to 300 kilograms per square centimeter. Typically thirty percent to fifty weight percent hydrogen peroxide will be used as the oxidant in carrying out the "hydrogenation" process. However, it is also possible to use oxygen, air or other oxidants such as cumyl hydroperoxide, tertiary butyl hydroperoxide, p-methane hydroperoxide and the like. A wide variety of metals that have ions or salts that will react with hydrazine can be used as the metal ion activator. Antimony, arsenic, bismuth, cerium, chromium, cobalt, copper, gold, iron, lead, manganese, mercury, molybdenum, nickel, osmium, palladium, platinum, cerium, silver, tellurium, tin and vanadium are representative of metal ions that will react with the hydrazine that are useful in the "hydrogenation step" as the metal ion activator. Iron and copper are the preferred metal ion activators, copper being especially preferred. Any solvent that does not detrimentally affect the latex stability of the "hydrogenation" reaction and the catalyst may be present in small amounts. Preferably, a solvent is used that does not interfere with the ozonation or subsequent oximation step. An acceptable solvent is toluene. However, it is preferred that there is no solvent present. These hydrogenated rubbers will typically have a saturation level of about 1 percent to about 99 percent. However, it is preferred that the hydrogenated rubber has a saturation level of about 85 percent to about 90 percent of its olefin content (derived from diene monomer). The reduction reaction can be conveniently followed by infrared spectroscopy (FTIR) or by Nuclear Magnetic Resonance techniques. The ozone is simply mixed with the latex containing the hydrogenated polymer for a period of time which is sufficient to achieve the desired results. This can be achieved by bubbling ozone through the latex. It can also be carried out by rapidly stirring the latex under an atmosphere containing ozone. It may be desirable that the ozone-containing atmosphere be under pressure. Other techniques can also be used to mix the ozone completely with the latex being treated. The temperature at which the ozone treatment step is carried out is not critical. In fact, virtually any temperature between the latex freezing temperature and its boiling temperature can be used. However, for practical reasons, the latex will normally be treated with ozone at a temperature that falls within the range of about 0 ° C to about 80 ° C. A temperature within the range of about 15 ° C to about 40 ° C will be particularly preferred. Higher temperatures can result in reduced ozone solubility in the latex even when faster reaction regimes can be achieved. The ozone treatment will be carried out for a period of time that will be sufficient to eliminate the undesirable levels of crosslinking. The treatment time employed will typically be within the range of about 15 minutes to about 6 hours, depending on the ozone content of the gas, the olefin content of the polymer and the degree of dissociation desired. The period of time used to treat the latex with ozone will be more typically within the range of about 30 minutes to about 2 hours. The gelation that can occur during the hydrogenation step is essentially due to a poorly defined cross-linking reaction of the elastomeric polymer in the emulsion. By treating the emulsion of the elastomeric polymer crosslinked with ozone, a reaction of azonolysis occurs. In this azonolysis reaction, the remaining double bonds in the crosslinked rubber are attacked with azonides that are formed. The ozonides formed under the condition of low temperature of the reaction are highly unstable and are destroyed by caustic hydrolysis with the water in the latex. The caustic hydrolysis of ozonides is known to produce equal molar amounts of carboxylic acid and terminal aldehyde groups. The groups terminated with carboxylic acid do not present a problem as the aldehyde end groups. The FTIR analysis technique has proven to be useful to qualitatively monitor the transformation of the functional group during the different stages of the process. For example, the aldehyde and carboxyl functionality generated in the polymer during ozonolysis can be easily seen. Further changes are apparent when the terminal aldehyde groups are reacted with the hydroxylamine. The ozonized latex containing the elastomeric polymer having at least one terminal aldehyde group is then treated with hydroxylamine in an amount and under conditions which are sufficient to react with the aldehyde end groups of the elastomeric polymer to produce oxime end groups . The amount of hydroxylamine that is used can vary. Generally speaking, the amount of hydroxylamine can vary from about 1 to 5 moles per mole of the aldehyde end groups of the elastomeric polymer. Preferably, the amount of hydroxylamine ranges from about 1 to 2 moles per mole of aldehyde end groups. The hydroxylamine that is preferably used is a salt-free base. In addition, the hydroxylamine is preferably an aqueous solution. A particularly preferred 50 percent aqueous solution of salt-free hydroxylamine can be obtained commercially from Howard Hall Division of R. W. Greef & amp;; Co., Inc. under the designation FH-50. The ozonized latex is preferably treated with the hydroxylamine under stirring at a temperature ranging from about 25 ° C to about 80 ° C. Preferably, the reaction temperature is about 50 ° C. at 75 ° C. The hydroxylamine treatment will be carried out for a period of time which is sufficient to convert any of the aldehyde end groups of the elastomeric polymer to oxime end groups. The treatment time will typically be within the range of approximately half an hour to 5 hours. The period of time used to treat ozonized latex with hydroxylamine will more typically fall within the range of about 1 hour to 2 hours. After the ozonized latex has been treated with hydroxylamine to form an approximate polymer latex, the latex is coagulated in a conventional manner. Normal procedures such as salt / acid coagulation procedures, aluminum sulfate or alcohol solution can be used. After the coagulation has been completed, the coagulated hydrogenated rubber can be dried in a conventional manner such as in an oven.

Example 1 I. Preparation of NBR Latex Using techniques and ingredients of the emulsion polymerization in general, an acrylonitrile / butadiene latex containing 1.5 parts by weight of the polymerizable antioxidant monomer, N- (4-anilino-phenyl) methacrylamide was polymerized to essentially 100 percent conversion to 18 ° C. The polymer latex had the following properties: Conversion approximately 100 percent Solids Percentage 39.7 Brookfield Viscosity (centipoises) 22.5 Surface Tension (dynes / centimeter) 54.0 Particle Size: # average (nm) 72.4 Volume Average (nm) 79.9 Analysis of the polymer isolated from this latex provided the following results: of Acrylonitrile Retained 39.0 percent Viscosity of Diluted Solution (dl / g) 0.422 Molecular Weight Mn approximately 13,000 Mw approximately 42,000 Total Gel Percentage about 1 percent II. Reduction A 5-liter three-necked round bottom flask equipped with a mechanical paddle stirrer, thermometer, reflux condenser and an inlet tube to feed the hydrogen peroxide solution was charged with 1312.5 grams of NBR latex ( 491.4 grams of rubber). This amount of rubber was calculated to contain 5,551 moles of double bonds. To the stirred latex at room temperature 277.55 grams of 64 percent aqueous hydrazine (5.551 moles, 100 percent of the theoretical amount based on moles of the double bonds present) and a mixture of 2.78 grams of Poly-Terg 2EP ( R) (a 48 percent disodium dodecyldiphenylether disulfonate active aqueous solution) and 2.78 grams of 4.97 percent copper sulphate pentahydrate solution (0.0005551 mol cupric ion). The mixture was heated in a constant temperature bath to 40 ° to 50 ° C before starting the addition of 410 grams (5.96 moles) of the aqueous hydrogen peroxide to 49.4 percent by drops by means of a syringe pump through of a period of 16 hours. The analysis of the reduced polymer indicated that a reduction from approximately 85 percent to 90 percent of the double bonds had been achieved. • The Mooney viscosity of the dry coagulated isopropanol rubber was found to be 127.

III. Ozonation Through the aforementioned reduced latex, 0.061 mol of ozone was passed as an air / ozone mixture at a temperature of 40 ° C to 50 ° C using a glass tube to introduce the gas near the bottom of the agitated latex. The flask was then heated to a temperature of 70 ° to 75 ° C.

IV. Oximation To the heated latex were then added 0.122 mol of a 50 percent aqueous solution of the salt-free hydroxylamine. The mixture was allowed to react for one hour before a small portion of latex was removed for coagulation and determination of the Mooney viscosity. The dried polymer was determined to have a ML-4 value of 98. The passage of an additional 0.030 mole of ozone through the latex followed by an additional 0.061 mole of 50 percent aqueous hydroxylamine resulted in an ML-4 value of 45 for isolated rubber.

Example 2 A duplicate reduction of that of Example 1 was carried out. The latex was then treated with 0.0763 mol of ozone as previously followed by the addition of 0.183 mol of the 50 percent hydroxylamine solution. After being reacted for 2 hours at 70 ° C to 75 ° C, a sample was isolated and its ML-4-value as being 65 was determined.

Claims (11)

CLAIMS:

1. A process for the preparation of a latex of a hydrogenated elastomeric polymer comprising: (1) combining an unsaturated polymer in the form of a latex with (a) an oxidant selected from the group consisting of oxygen, air and hydroperoxide; (b) a reducing agent that is selected from hydrazine and hydrates thereof; and (c) a metal ion activator; (2) heating the mixture at a temperature of 0 ° C to the reflux temperature of the reaction mixture; (3) treating the mixture with ozone in an amount and under conditions which are sufficient for the ozone to react with the residual polymer unsaturation to form an ozonized latex of an elastomeric polymer having at least one terminal aldehyde group; (4) treating the ozonized latex with hydroxylamine in an amount and under conditions which are sufficient to convert the aldehyde end groups of the elastomeric polymer into the oxime end groups in order to form an approximate polymer latex.

2. The process according to claim 1, wherein the polymer latex is coagulated.

3. The process according to claim 2, wherein the polymer latex is dried after coagulation

4. The process according to claim 1, wherein the amount of hydroxylamine to be reacted ranges from about 1 mol to 5 moles per mole of the aldehyde end groups.

5. The process according to claim 1, wherein the ozonized latex is treated with hydroxylamine at a temperature ranging from about 50 ° C to 75 ° C.

6. The process according to claim 1, wherein the oxidized latex is treated with hydroxylamine for a period of time ranging from about half an hour to 5 hours.

7. The process according to claim 1, wherein the hydroxylamine is free of salt. The process according to claim 1, wherein the unsaturated polymer in the form of latex is prepared from 5 percent to 100 percent by weight of conjugated units of diene monomer and from 95 percent to 0 percent by weight of ethylenically unsaturated monomer units. 9. The process according to claim 1, wherein the unsaturated polymer is NBR. 10. An oxymer polymer latex prepared in accordance with claim 1. 11. A dried hydrogenated rubber that is prepared according to claim 3.