Patent Publication Number: US-4929711-A

Title: Process for converting polyketones to polyesters

Description:
FIELD OF THE INVENTION: 
     The present invention relates to a process for converting polyketones to polyesters. More particularly, the invention involves a process whereby carbonyl (ketone) groups in the polymer chain are oxidatively converted to oxycarbonyl (ester) moieties. 
     BACKGROUND OF THE INVENTION: 
     Polyketones, i.e., polymers having carbonyl groups incorporated in the polymer chain, are known and are most commonly produced by polymerizing carbon monoxide with one or more α-olefins. Polyketones of this type derived from ethylene and carbon monoxide were disclosed by Brubaker in U.S. Pat. No. 2,495,286. Numerous other liquid and gas phase procedures utilizing Ziegler and radical catalysts have been described in the prior art for polymerizing carbon monoxide with ethylene and other olefinically unsaturated monomers. A general review of the properties, preparations, reactions and uses of olefin-carbon monoxide copolymers can be found in the Encyclopedia of Polymer Science and Technology, Vol. 9, p. 397-402, John Wiley &amp; Sons, Inc. (1968). 
     Various procedures are known for the chemical modification of polyketones. U.S. Pat. No. 2,457,271 discloses a method for modifying monoolefin-carbon monoxide copolymers to increase the degree of unsaturation by heating the copolymer in a solution of an organic solvent with a minor amount of an alkali metal hydroxide. The copolymer is reacted until the oxygen content is decreased by at least 5% or the iodine number increased to at least 25. Modification of polyketones (monoolefin-carbon monoxide copolymers) by reaction with hydrazine hydrate and related nitrogen-containing compounds is described in U.S. Pat. No. 2,457,279. A process for reacting polyketones with hydrogen cyanide to prepare polycyanohydrin resins is disclosed in U.S. Pat. No. 2,495,284. 
     U.S. Pat. No. 2,495,292 discloses the catalytic hydrogenation of monoolefin-carbon monoxide polymers in the presence of a nickel catalyst to reduce the carbonyl groups to secondary alcohol groups and obtain high molecular weight polyhydric alcohols. U. S. Pat. No. 2,846,406 relates to a process for reacting monoolefin-carbon monoxide copolymers with formaldehyde and specific ammonium or amine salts to produce polyamines of relatively high molecular weight. Another process for modifying monoolefin-carbon monoxide copolymers by reaction with hydrazoic acid in the presence of an acid catalyst is disclosed in U.S. Pat. No. 3,068,201. 
     Processes for producing thermoplastic polymers from polyketones are also disclosed in U.S. Pat. Nos. 3,979,373 and 3,979,374. The products of U.S. Pat. No. 3,979,373 are polymeric furan derivatives obtained by reacting an equimolar alternate copolymer of ethylene and carbon monoxide with a strong acid, e.g. sulfuric, phosphoric, p-toluene sulfonic, etc., at 40°-200° C. The polymeric pyrrollic polymers of U.S. Pat. No. 3,979,374 are obtained by reacting an equimolar alternate copolymer of ethylene and carbon monoxide with a primary monoamine in the presence of strong acid and a solvent at a temperature from 40°-100° C. 
     U.S. Pat. Nos. 4,616,072 and 4,687,805 disclose halogenating ethylene-carbon monoxide copolymers by contacting said copolymers in a liquid medium and in the presence of an anionic halogenation catalyst selected from Lewis acids and Lewis bases. 
     The oxidation and chain cleavage of ethylene-carbon monoxide copolymers to produce mixtures of α,ω-dicarboxylic acids ranging from succinic acid through dodecanedioic acid and possibly higher and their corresponding esters is disclosed in U.S. Pat. No. 2,436,269. The oxidation is typically accomplished utilizing nitric acid and a vanadium oxidation catalyst, e.g. vanadium pentoxide or ammonium vanadate. Other oxidizing agents which are disclosed include the higher oxides of nitrogen, chromic acid, permanganates, molecular oxygen or air, or mixtures of these. 
     It would be highly advantageous if a process were available whereby carbonyl groups incorporated in a polymer chain, such as with polyketones, could be readily oxidized to ester groups. It would be even more advantageous if this conversion could be accomplished without significant cleavage of the polymer chain, i.e., without substantially altering the molecular weight and molecular weight distribution of the polymer. It would be still more advantageous if the degree of oxidation could be easily controlled so that substantially all or only a portion of the carbonyl groups could be converted to oxycarbonyl moieties. These and other advantages are realized by the process of the present invention and will be described in more detail to follow. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a process for converting a polyketone to a polyester by oxidizing carbonyl groups present in the polymer chain to oxycarbonyl groups. The reaction is accomplished without significant chain scission so that the molecular weight and molecular weight distribution of the polymer are not substantially altered. More specifically, the process involves contacting a polyketone of molecular weight greater than 1,000 and having a carbonyl content of from 0.01% to 50% by weight with an organic peroxyacid oxidizing agent having from 1 to 20 carbon atoms in an inert liquid medium at a temperature from -20° C. to 150° C. The molar ratio of organic peroxyacid to carbonyl can range from 0.1:1 to 30:1 and the weight ratio of the inert liquid medium to polyketone can range from 1:1 to 100:1. Substantially all or only a portion of the carbonyl functionality of the polyketone can be converted to ester groups. 
     In a particularly useful embodiment of the invention, the polyketone will have a molecular weight from about 10,000 to 1,000,000 and carbonyl content from 0.5 to 20 weight percent. Organic peroxyacids which are especially useful oxidizing agents include chloro-, fluoro-, and carboxyl-substituted aromatic or aliphatic peroxyacids. These peroxyacids are particularly effective for the process when employed at molar ratios from 2:1 to 15:1 (peroxyacid:carbonyl). The process is highly useful for the conversion of polymers of ethylene and carbon monoxide to the corresponding polyesters, including ethylene-carbon monoxide copolymers and terpolymers of ethylene, carbon monoxide and a C 3-8  α-olefin. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention broadly relates to a process for converting polyketones to polyesters. As employed herein the term polyketone generally refers to polymers having a plurality of carbonyl ##STR1## groups in the polymer chain. The carbonyl groups, sometimes also referred to herein as ketone or keto groups, may be randomly or uniformly distributed throughout the polymer chain. 
     The term polyester is used herein in a generic sense and encompasses any polymer having one or more oxycarbonyl ##STR2## groups in the polymer chain. The polyesters will typically contain a plurality of oxycarbonyl groups, also referred to herein as ester groups. When less than all of the available carbonyl functionality of the polyketone is reacted, the polyesters will contain both oxycarbonyl and carbonyl groups. As will be apparent to those skilled in the art, a broad array of useful polyester products can therefore be produced by the present process. It is a highly desirable aspect of the present invention that by judicious selection of the process variables, it is possible to vary the composition of the resulting product with respect to the amount of carbonyl and oxycarbonyl groups present therein thus making it possible &#34;tailor&#34; products to meet pre-determined specifications. 
     Considering the reaction of only a single carbonyl group within a polyketone molecule derived from the copolymerization of ethylene and carbon monoxide, the process of the present invention can be represented as follows: ##STR3## where x is an integer representing the number of adjoining ethylene units at a particular CO site. As is evident from the above equation, insertion of the oxygen atom can occur on either side of the carbonyl. 
     While it is possible to obtain quantitative conversion of the carbonyl to oxycarbonyl groups, it is not necessary. Substantial amounts of carbonyl functionality may remain and be present in the resulting polyester product. For example, if the above-depicted reaction sequence is adapted to a situation where only a portion of the carbonyl groups in a polyketone produced by the copolymerization of ethylene and carbon monoxide is reacted, the reaction showing one possible molecular configuration which could result can be represented as follows: ##STR4## where x and y are integers, which can be the same or different, representing the number of ethylene units. 
     The polyketone polymers utilized for the preparation of the polyesters in accordance with the process of the present invention comprise a hydrocarbon polymer chain having a plurality of carbonyl groups distributed throughout with the carbon atom of the carbonyl being part of the polymer chain. The polymer chain is comprised substantially entirely of carbon atoms. The carbonyl groups may be either randomly or uniformly distributed within the polymer molecule, i.e. along the polymer backbone. The polyketones can structurally be represented as being comprised of repeating units of the structural formula ##STR5## where R represents a bivalent hydrocarbon moiety. 
     The molecular weight of the polyketones can range from about 1,000 up to several million or more. It is possible to react extremely high molecular weight polyketones (up to 5 million) in accordance with the present process to convert all or a portion of the carbonyl functionality to ester functionality. Most commonly, the polyketones will have molecular weights from 1,000 to 2,000,000 and, more particularly, from about 10,000 up to about 1,000,000. The carbonyl content (% CO) of the polyketones will range from 0.01 weight percent up to about 50 weight percent. Most usually, carbonyl contents range from 0.5 weight percent up to about 20 weight percent. 
     Useful polyketones can be obtained by any of the known procedures described in the art. The method of preparation of the polyketone plays no role in the process of the invention so long as the polyketone is substantially free of impurities, such as catalyst residues or the like, which might interfere with the oxidation reaction. While the polyketones are most advantageously prepared by the copolymerization of carbon monoxide and α-olefins, other procedures can be utilized. These include, for example, copolymerization of ethylene with aliphatic aldehydes at high temperature and pressure; oxidation of polyvinylalcohol or polyethylene; cationic polymerization of ketene or diketene; radical ring-opening polymerization of unsaturated cyclic ethers or diketene; and radical ring-opening polymerization of 2,2-diphenyl-4-methylene-1,3-dioxolane. 
     Copolymerization of carbon monoxide and α-olefins or mixtures of α-olefins is most commonly utilized to produce the polyketones. Numerous procedures for preparation of these polymers are known and described in the prior art. The α-olefins which are used typically have from 2 to 12 carbon atoms and include aliphatic α-olefins, such as ethylene, propylene, butene-1, isobutylene, hexene-1, octene-1, and α-olefins having aromatic substituents, such as styrene, p-methyl styrene, α-methyl styrene and the like. Polyketones obtained by the polymerization of carbon monoxide and ethylene or the polymerization of carbon monoxide, ethylene and a second α-olefin having from 3 to 8 carbon atoms, and particularly propylene, are most advantageously utilized in the present process. 
     The process of the present invention may also be advantageously used with other polymers having carbonyl groups present in the polymer chain and derived from one or more olefinically unsaturated monomers such as styrene; α-methylstyrene; α-olefins; acrylonitrile; acrylamide; vinyl chloride; vinylidene chloride; vinyl acetate; methyl vinyl ketone; vinylpyridine; acrylic acid and esters thereof; methacrylic acid and esters thereof; maleic anhydride and mono- and diesters thereof; and the like. 
     The physical characteristics of the resulting polyester are a function of the molecular weight and the molecular weight distribution of the polymer and the extent of conversion of carbonyl groups to oxycarbonyl groups. These in turn primarily depend on the composition of the polyketone, the reaction conditions, and the amount of oxidizing agent used. 
     For the process of this invention, the reaction is carried out in an inert liquid medium, that is, a material which is a liquid at the reaction temperature and which does not react with either the polyketone or the polyester and which is not oxidized under the reaction conditions. Additionally, the liquid must be one which is either capable of dissolving or swelling the polymer. While the boiling point of the liquid medium is not critical, the boiling point should not be so high as to make removal of the solvent difficult. When liquids with boiling points lower than the reaction temperature are used for the process, the reaction can be run under reflux conditions or in a pressure vessel. 
     Useful mediums for the reaction include hydrocarbons, chlorinated hydrocarbons, nitrohydrocarbons, carboxylic acids and carboxylic acid esters. Hexane, heptane, octane, benzene, decalin, methylene chloride, chlorobenzene, dichlorobenzene, nitrobenzene and dimethylphthalate are illustrative of the compounds which can be used as the reaction medium for the process. Aliphatic (C 5-10 ) hydrocarbons, benzene, chlorinated C 1-3  aliphatic hydrocarbons, chlorobenzene and dichlorobenzene are particularly advantageous for the process. 
     The weight ratio of the liquid medium to polyketone can vary over broad limits but most typically will range from 1:1 to 100:1. The weight ratio of liquid to polyketone most generally ranges from 5:1 up to about 50:1. 
     An oxidizing agent is necessarily utilized for the process and is dispersed or dissolved in the inert liquid medium and contacted with the polyketone. The molar ratio of oxidizing agent based on the carbonyl functionality ranges from about 0.1:1 to 30:1 and, most preferably, from 2:1 to 15:1. This is the number of moles of oxidizing agent per mole of carbonyl group. Organic peroxyacids are employed as the oxidizing agent for the present process. 
     Useful organic peroxyacids for the invention contain from 2 up to about 30 carbon atoms and correspond to the formula ##STR6## where R&#39; is an aliphatic, cycloaliphatic or aromatic moiety which can be unsubstituted or substituted with one or more halo, nitro or carboxyl groups. When R&#39; is aliphatic, i.e. an alkyl group, it will generally contain from 1 to 19 carbon atoms. When R&#39; is cycloaliphatic, i.e., a cycloalkyl group, it will generally contain from 5 to 19 carbon atoms. When R&#39; is aromatic, i.e. an aryl group, it will generally contain from 6 to 19 carbon atoms. As previously indicated, any of said alkyl, cycloalkyl or aryl groups can contain halo-, nitro- or carboxyl-substituents. Chloro and fluoro groups are particularly advantageous halo substituents. In a particularly useful embodiment, the organic peroxyacid oxidizing agent is a chloro-, fluoro- or carboxyl-substituted aromatic or aliphatic peroxyacid. Peroxybenzoic acid, m-chloroperoxybenzoic acid, peroxyacetic acid, trifluoroperoxyacetic acid, monoperoxyphthalic acid and monoperoxymaleic acid are representative of the oxidizing agents which can be used. m-Chloroperoxybenzoic acid and monoperoxymaleic acid have been found to be particularly advantageous. The peroxyacid can be used as such, or formed in situ, e.g. by the reaction of maleic anhydride with hydrogen peroxide. 
     The reaction can be conducted at temperatures from about -20° C. up to about 150° C., however, it is generally considered most advantageous to carry out the reaction at a temperature from about 20° C. to 100° C. While reaction times will vary depending on the reactants and liquid medium used and the reaction temperature, it can range from 30 minutes under optimal or near optimal conditions up to 24 hours or more where low reaction temperatures and/or low concentrations of reactants are used. 
     The reaction conditions and time of reaction will be selected based on the degree of conversion of carbonyl to oxycarbonyl desired. As previously pointed out, all or substantially all of the available carbonyl groups of the polyketone can be converted to ester moieties, if desired. However, since it is not necessary to achieve 100% conversion and in certain instances is advantageous to produce polyester products which contain both oxycarbonyl and carbonyl moieties, the process is generally conducted in such a way that only a portion of the keto functionality is converted to ester groups. This permits the use of reaction times and conditions which minimize or completely eliminate undesirable chain scission reactions. 
     Most commonly the reaction is carried to no more than 90% conversion of the keto groups. 
     The polyester products prepared in accordance with the invention, whether they contain only oxycarbonyl moieties or both carbonyl and oxycarbonyl groups, are recovered utilizing conventional procedures known to the art. Generally, the polymer solution or polymer dispersion is cooled to ambient conditions to precipitate the polymer which is then recovered by filtration. To facilitate this precipitation, precipitating diluents which are non-solvents for the polyester, i.e. do not dissolve or swell the polymer, can be added. Such precipitating diluents include but are not limited to methanol, ethanol, propanol, t-butanol, acetone and the like. Since excess oxidizing agent and by-products formed as a result of the reaction, e.g. carboxylic acids, may be precipitated with the polyester it may be advantageous to re-dissolve the polymer in a solvent, such as toluene or xylene, and re-precipitate by the addition of one or more of the aforementioned precipitating diluents. The recovered polymer is then dried and, if desired, additives incorporated therein. 
     It is known that the substrate polyketones, particularly ethylene-carbon monoxide copolymers, exhibit photodegradability due to absorption of radiation by the carbonyl chromophore (Comprehensive Polymer Science, Vol 6, p. 530, Pergamon Press); however, the polyester products obtained according to the present process which result from the partial conversion of carbonyl to oxycarbonyl moieties are both photodegradable and biodegradable. This is a particularly useful combination of properties. 
     The biodegradable polyesters obtained in accordance with the present process are highly useful as plastics and waxes, the degree of biodegradability increasing with increasing percent conversion of main-chain carbonyl groups to oxycarbonyl moieties. The present products are also useful as adhesives and coatings. 
     The following examples illustrate the invention more fully; however, they are not intended as a limitation on the scope thereof. In the examples all parts, percentages and ratios are on a weight basis unless otherwise indicated. 
    
    
     EXAMPLE I 
     Ten grams of a polyketone (ethylene-carbon monoxide (ECO) copolymer resin powder containing 1.6% carbon monoxide; Mw 125,000; Mn 18,000) and 2.0 grams m-chloroperoxybenzoic acid (MCPBA) were charged to a flask containing 50 mls heptane and dissolved therein. The ratio of heptane to polyketone was 3.4:1 and the molar ratio of the oxidizing agent to carbonyl (CO) was 2.1:1. The reaction mixture was stirred for 2 hours at 80° C. and then cooled to room temperature. Methanol (250 mls) was added to precipitate the polymer. The polymer was recovered by filtration, washed with methanol and dried at room temperature under vacuum. Analysis of the resulting product by infrared spectroscopy showed a strong absorption at 1735 cm -1  attributable to the presence of ester carbonyl. The infrared spectrum also showed a significant decrease in the ketone carbonyl absorption at 1710 cm -1  compared to the starting polyketone. Based on the relative heights of the infrared absorption peaks, conversion of carbonyl to oxycarbonyl was calculated to be 90%. Ester formation was also confirmed by nuclear magnetic resonance spectroscopy. 
     EXAMPLE II 
     The procedure of Example I was repeated on a larger scale. Reactants used were the same except that the ratio of heptane to ECO copolymer was 2.4:1 and the molar ratio of m-chloroperoxybenzoic acid to carbonyl was 2.0:1. After 2 hours reaction at 80° C. approximately 80% of the carbonyl groups of the polyketone were converted to oxycarbonyl groups. The resulting polyester product (tensile strength at yield 1650 psi, elongation 540%) was useful for the preparation of sheet, film and molded articles. 
     EXAMPLES III-VIII 
     To further demonstrate the ability to vary the process, a series of reactions were conducted following the general procedure of Example I. Process details and results obtained, i.e., degree of conversion of carbonyl to oxycarbonyl, are set forth in Table I. It is apparent from the data that a variety of solvents and conditions can be utilized for the oxidation reaction and that a wide variety of polyester products can be produced. 
     
                                           TABLE I                                 
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     Molar Ratio             Reaction Temp                                
                                     Reaction Time                        
Example                                                                   
     MCPBA:CO                                                             
            Diluent   Diluent:ECO                                         
                             (°C.)                                 
                                     (hours) % Conversion                 
__________________________________________________________________________
                                             6                            
III  13.4:1 Chlorobenzene                                                 
                      11.1:1 70      20      80%                          
IV   6.8:1  Toluene   8.7:1  50      24      20%                          
V    6.8:1  Ethyl Acetate                                                 
                      9.0:1  70      24      15%                          
VI   6.8:1  Decalin   9.0:1  50      24      20%                          
VII  6.8:1  Dimethylphthalate                                             
                      11.9:1 70      24      50%                          
VIII 6.8:1  Heptane   6.8:1  70      24      90%                          
__________________________________________________________________________
 
    
     EXAMPLE IX 
     A low molecular weight polyketone was oxidized using monoperoxymaleic acid. The monoperoxymaleic acid was prepared by reacting (1 hour at 40° C. with stirring) 26 mls 30% aqueous hydrogen peroxide with 56.0 grams maleic anhydride in 125 mls methylene chloride. The solid maleic acid formed was collected on a filter and the filtrate containing monoperoxymaleic acid was added to a chlorobenzene solution of the polyketone. The solution was obtained by dissolving 5.0 grams ethylene-carbon monoxide copolymer (powder; 36.6% CO; Mw 3,700; Mn 1,970) in 100 mls chlorobenzene. After stirring for 24 hours at 70° C., the mixture was cooled and filtered and 500 mls methanol added to the filtrate to precipitate the polyester. After washing with methanol, the polyester was dissolved in toluene and re-precipitated using methanol. Conversion of keto functionality to ester functionality was calculated to be 20% based on a comparison of the relative intensities of the infrared absorption peaks. 
     EXAMPLES X-XIII 
     A series of low molecular weight ethylene-carbon monoxide (ECO) copolymers of varying carbonyl content were oxidized to the corresponding polyesters in accordance with the general procedure of the invention. In each instance 90% of the carbonyl functionality was converted to oxycarbonyl groups. The oxidizing agent used was m-chloroperoxybenzoic (MCPBA) acid and the diluent was chlorobenzene. Characteristics of the ECO copolymers and reaction particulars are set forth in Table II. 
     
                                           TABLE II                                
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ECO            Molar Ratio   Reaction                                     
                                    Reaction                              
Example                                                                   
     Mw Mn % CO                                                           
               MCPBA:CO                                                   
                      Diluent:ECO                                         
                             Temp. (°C.)                           
                                    Time (hours)                          
__________________________________________________________________________
X    2,510                                                                
        1,240                                                             
           13.0                                                           
               2.1:1  11.1:1 70     24                                    
XI   2,300                                                                
        1,260                                                             
            3.2                                                           
               4.4:1  11.1:1 70     24                                    
XII  2,190                                                                
        1,040                                                             
            5.9                                                           
               2.7:1   7.9:1 70     16                                    
XIII 2,270                                                                
        1,130                                                             
           10.0                                                           
               2.5:1    13:1 70     20                                    
__________________________________________________________________________
 
    
     EXAMPLE XIV 
     Ethylene-carbon monoxide copolymer pellets (1.6% CO; Mw 125,000; Mn 18,000) were suspended in 10 mls chlorobenzene with 1.6 grams m-chloroperoxybenzoic acid in a glass vessel. The molar ratio of oxidizing agent to carbonyl was 8.3:1 and the ratio of solvent to copolymer resin was 5.9:1. The container was sealed and rolled for 90 hours on a roller mill under ambient conditions. The swelled polymer pellets (recovered by filtration) were washed with toluene then methanol and purified by dissolving in toluene followed by precipitation with methanol. Infrared analysis of the dried polymer product showed a strong ester carbonyl absorption at 1735 cm -1 .Based on the relative intensities of the keto and ester peaks the conversion of ketone to ester functionality was calculated to be 35%. 
     EXAMPLE XV 
     Ethylene-carbon monoxide copolymer powder (1.6 % CO; Mw 125,000; Mn 18,000) was combined with chlorobenzene (weight ratio 7.7:1) and m-chloroperoxybenzoic acid (molar ratio 8.8:1) and stirred for 7 days at room temperature. Approximately fifty percent of the ketone groups of the polyketone converted to ester groups. Expressed in different terms, the resulting polyester product had carbonyl and oxycarboxyl groups, present in essentially a 1:1 ratio randomly distributed throughout the polymer chain. 
     EXAMPLE XVI 
     One gram of the polyketone of Example XV was dissolved in 25 mls chlorobenzene by heating at 90° C. The solution was cooled to 65° C. and 3.0 grams maleic anhydride and 2.0 grams 30% aqueous hydrogen peroxide added thereto. The reaction mixture was maintained at 65° C. for 21 hours with stirring after which time the polymer was precipitated by cooling the mixture and the addition of 50 mls. methanol. The recovered polymer was dissolved in 50 mls toluene and reprecipitated using methanol. The infrared spectrum of the dried polymer showed an ester peak at 1735 cm -1  ; the conversion of carbonyl to oxycarbonyl was calculated to be 20%.