US3160484A

US3160484A - Stabilizing additives for distillate furels

Info

Publication number: US3160484A
Application number: US126531A
Authority: US
Inventors: Joel R Siegel
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1961-07-25
Filing date: 1961-07-25
Publication date: 1964-12-08
Anticipated expiration: 1981-12-08
Also published as: BE569574A; NL97760C; FR1207570A

Description

United States Patent 3,160,484 STABlLIZING ADDlaiglS FOR DISHLLATE F S Joel R. Siege], Elizabeth, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Continuation of application Ser. No.

673,156, duly 22, 1957. This application July 25,

1%1, Ser. No. 126,531

a 26 Claims. (Cl. 44-62) The present invention relates to a new class of additives for use in petroleum distillate fuel products. cifically, it relates to a new class of copolymers containing chlorine and to the use of such copolymers as additives for stabilizing petroleum distillate fuels. This application is a continuation of Serial .No. 673,156, filed July 22, 1957.

It has long been recognized that heating oils, jet engine fuels and other middle distillate fuel products derived from petroleum often contain unstable compounds which tend to decompose and form sludge and sediment during storage, Fuels containing partially unsaturated stocks derived from thermal or catalytic cracking operations in quantities exceeding about percent by volume are especially subject to such sludging and sedimentation. A

number of different materials have been proposed 'here tofore for incorporation into such fuels in order to overcome their instability and avoid the plugging and fouling of fuel lines, filters and nozzles due to sediment and sludge. The most successful of these materials have been metallic compounds such as metal naphthena-tes, metal sulfonates, and metal salts of alkyl metal sulfides. Such metallic compounds, although eiiective for stabilizing fuels, are unsatisfactory because they leave a residue when burned. This residue leads to a gradual buildup of deposits in combination chambers and burner systems which materially decrease combustion efiiciencyu Various ashless compounds have been suggested in orderto overcome these difliculties but have not been found wholly effective.

The present invention provides a new class of ashless additives containing chlorine which are effective in very small quantities for inhibiting the formation of sludge and sediment in petroleum distillate fuels boiling in the range between about 300 and about 900 F. Typical'of such fuels are heating oils meeting the requirements'for Grades 1 and 2 fuel oils as set forth in ASTM Specification D-3 9648T, diesel fuels falling Within Grades 1D, 2D and 4D of ASTM Specification D-97551T, and jet engine fuels such as those covered by US. Military Specification lviIL-F-5624C. The addition of as little as about 0.002 percent by weight of the additive materials of the invention significantly improves the stability of such fuelsand extends the period for which they may be satisfactorily stored under adverse conditions.

The stabilizing additives of this invention are chlorinecontaining copolymers containing ester groups derived from the reaction of epichlorohydrin with a carboxylic acid group. These copolymers may be prepared by co polymerizing with other polymerizable monomers or mix- More spe- 3,160,484 Patented Dec. 8, 1 964 The mixed esters which have been found useful in preparing copolymers for stabilizing petroleum distillate fuels in accordance with the invention are long chain saturated aliphatic alcohol-epichlorohydrin mixed esters of unsaturated conjugated dibasic zacids. These esters, re-' ferred to hereinafter as alkyl-chloropropyleneoxy mixed esters are thought to have the general formula:

l l RO-G?=CCO(CH2CHO)DH R! RI! H201 where R is an alkyl group containing from about 8 to about 24 carbon atoms; R and R" are constituents selected from the class consisting of hydrogen atoms and methyl groups, at least one such constituent being a hydrogen atom; and 11 may vary from one to three or more, depending upon the quantity of epichlorohydrin employed in preparing the esters. I

The alkyl-chloropropyleneoxy mixed esters employed in preparing the 'copolymers of the invention may be readily obtained by first reacting an unsaturated 0011-. jugated dibasic acid with a long chain saturated aliphatic alcohol to form a half ester and then reacting this product with epichlorohydrin in the presence of an acidic (electron acceptor) catalyst to produce the mixed ester. The addition of epichlorohydrin to the half .ester may also be catalyzed by basic groups, e.g. CH O, OH. Suitable unsaturated conjugated dibasic acids forfpreparing the mixed esters in this manner include maleic acid, fumaric acid, citraconic acid, mesaconic acid, and mixtures of such acids. The butenedioic acids, i.e., maleic and fumaric acids and mixtures of the two, are preferred acids. It is preferable to employ the acids in the form of their anhydrides, in whichcasethe half ester can be produced by merely heating one mole of the an- I hydride with one mole of the long chain saturated alitures of such monomers the reaction product of epichlorohydrin with a polymerizable, unsaturated acid; i.e., dibasic acids such as maleic acid and half esters of dibasic acids suchas lauryl hydrogen maleate. The chlorine- 'containing copolymers of the invention may also be prepared by'the' reaction of epichlorohydrin with polymers phatic alcohol at a temperature of about to C. for about thirty to about forty-five minutes. Other wellknown methods for the production of half esters of dibasic acids may also be employed.

The long chain saturated aliphatic alcohols reacted with the dibasic acids or acid anhydrides to produce half esters may contain from about 8 to 24 carbon atoms per molecule, those containing ,from about 8 to about 18 carbon atoms being preferred. Straight chain primary alcohols such as dodecyl, cetyl, eicosyl and docosyl molecule and has the following approximate composiv tion:

Number of carbon atoms: Weight, percent C19 I C j 55 .5 7 C 22.5. C 14.0 (3 4.0

Lorol is thus a commercialmixture of saturated all-L phatic alcohols containing from 10 to. 1.8 atoms per molecule and having :an average chain length of J additives of the invention are normally obtained by the oxonation and hydrogenation of a C copolymer of propylene and butene. The copolymer itself is in reality a mixture of isomers and the resultant oxo-alcohol may have the following general analysis:

STRUCTURE or CE oxo-aLoonor. PREPARED FROM 03-04 COPOLYMER HEPTENES Highermolecular weight oxo-alcohols may also be used in preparing the additives of the invention. These higher molecular weight alcohols are believed to have compositions generally analogous to that specified above, chain lengths and degree of branching depending upon: the type of olefins used in preparing the copolymers.

The process used for the manufacture of oxo-alcohols is now well-known in the art and need not be further described.

The half esters prepared by reacting the dibasic acid and alcohol are in turn reacted with epichlorohydrin in 4 catalyst used was acidic or dilute acid if the catalyst was basic and then water washed.

The mixed esters prepared as described above are c0- polymerized witha polymerizable organic monomer containing a vinyl group in order to produce stabilizing additives for incorporation in petroleum distillate fuels. Suitable monomers containing vinyl groups include hydrocarbons such styrene; isobutylene, and butadiene; esters such as allyl acetate, vinyl propionate and methyl methacrylate; ethers such as allyl ethyl ether and divinyl ether; nitriles such as acrylonitrile and vinylacetonitrile. Mixtures of such monomers containing vinyl groups with other copolymerizable materials, long chain alcohol esters of unsaturatedconjugated dibasic acids such as lauryl maleate and tallow fumarate for example, may also be used. Vinyl esters of short chain fatty acids, particularly vinyl acetate, and mixtures of-such esters with fumarate or maleate esters of long chain aliphatic alcohols contain ing from about 8 to 20 carbon atoms per molecule are preferred monomers for the preparation of copolymers with the mixed esters i The copolymerization of the mixed ester with the organic monomer may be carried out in a solution of henzene or other suitable organic solvent ata temperature in the range of from about 60 to about 250 'F. and may be'promoted by gamma radiation or by the useof a peroxide type catalyst such as benzoyl peroxide, a hydroperoxide or an azo catalyst such as alpha-alpha' azo-bisisobutyronitrile. organic monomers in the polymerization mixture may be varied from about 2:1 toabout 1:20. The polymerizae tion may be carried out in a suitable solvent in order to control reaction velocity and molecular weight. Oxygen generally will beexcluded during the polymerization by the use of a blanket of an inert gas such as nitrogen or carbon dioxide. The polymerization time may vary from about 1 to '36 hours.

Polymerization of the mixed ester and the organic monomer proceeds between the unsaturated double bonds 'in theacid portion ofthe ester and in the monomer.

weightsof from about 6,000 to about 20,000 are par ticularly preferred. Upon completion of the polymerizathe presence of from about 0.05 to 5.0 percent by weight of an acidic (electron acceptor) catalyst such as boron trifluoride, boron trifluoride etherate,- aluminum' trichlo ride, aluminum tribromideflor the like or a basic catalyst such as NaOCH or NaOH. The reaction is carried 'out' by slowly adding the epichl'orohydrin to, the halfester mixed with catalyst over approximately a one to two hour period. The temperature at which the addition is carried out may range between about 100 C. and 180 e. The reactantsare held at this temperature from about '4 hours to about 24 hours or longer. 7 Depending upon the numberof chlorine atoms desired per molecule or mixed ester, the esterzepichlorohydrin ratio may range Jetween aboutlzl to about 1:4. Under these conditions ;he addition of the epichlorohydrin molecule to the half aster takesplace through the epoxy group and the chlofine atom of the epichlorohydrin is unaffected;

It is preferred that the half ester and the epichlorotion reaction, the copolymer may be freedo-f solvent and employed for the stabilizing of distillatefuels.

' The copolymer may be incorporated into petroleum distillate fuels in concentrations of from about 0.002 to about 2 percent by weight in order to stabilize such fuels.

. reacting, epichlorohydrin and isooctyl hydrogen maleate,

an acid-ester of isooetyl alcohol and maleic acid, in the presence of 0.05 wt. percent of a sodium methylate catalyst; One mole, of the, epichlorohydrin was added to one mole'of'the acid ester in a stirred reaction vessel con-5 taining the catalyst over a period of about one. hour. The

addition temperature was C. The reaction mixture was thenfmaintained at this temperature for a period of 7 hours. At the end of this time itwas foundthat substantially all the reactants had been converted to the mixed ester. A chlorine analysis of the product showed that the mixed ester contained essentially*oneepichlorohydrin The mole ratio of mixed ester to other I vinyl acetate.

group per molecule of the ester. The Total Acid Number and the Saponification Number of the product were as follows:

Cale. Found TAN, mg. KOH/gm 4. 9 SAP, mg. KOH/gm 525 433 EXAMPLE 2 Cale. Found TAN, mg. KOH/gm 0 3.1 SAP, mg. KOH/gm 525 437 EXAMPLE 3 Epichlorohydrin and isooctyl hydrogen maleate, an acid-ester of isooctyl alcohol and maleic acid, were reacted to form a mixed ester by adding to one mole of the half ester in (the presence of 0.5% by wt. of BF}; etherate one mole of epichlorohydrin over a period of about one hour. This was carried out with stirring at a temperature of about 150 C. This temperature was held for about 17 hours. Analysis of the mixed ester thus produced showed that the ester contained approximately one molecule of epichlorohydrin per molecule of ester. The Saponification Number and the Total Acid Number of the mixed ester, expressed as milligrams of KOH per gram of sample, were 417.8 and 9.1 respectively, as compared to calculated values of 525 and 0 respectively. A copolymer of this ester (.125 mole) with vinyl acetate (1 mole) and tallow fumarate (.875 mole), fumaric acid.

esterified with a mixture of saturated aliphatic alcohols containing from 16 to 18 carbon atoms per molecule, was

prepared by heating the reactants in an equal weight of benzene for about 3hours at 8090 C. in the presence of 1 weight percent of benzoyl peroxide.

' EXAMPLE 4 Employing the reactants of Example 3, a polymer containing 0.25 mole of isooctyl chloropropyleneoxy maleate and 0.75 mole of tallow fumarate per mole of vinyl acetate was prepared; The reaction conditions and catalyst were the same as those of Example 3 except that the mixture was heated for 1.5 hours.

EXAMPLE 5 Equimolar quantities of epichlorohydrin and tallow' hydrogen maleate were reacted to form a mixed ester in accordance with the method of Example 3. A. copolymer of this ester with vinyl acetate and tallow fumarate containing 0.125 moleof the mixed ester and 0.875 mole of tallow fumarate per mole of vinyl acetate was then prepared.

EXAMPLE 6 The reactants employed in Example 5 were copolym erized to give a copolymer containing 0.25 mole of a mixed ester and 0.75. mole of tallow fumarateper mole of EXAMPLE 7 Lorol hydrogen maleate, an acid ester of maleic acid and a mixture of saturated C to C aliphatic alcohols derived from the hydrogenation of coconut oil, was reacted with epichlorohydrin in equimolar quantities by heating the reactants after slow addition of the epichlorohydrin to the half ester in xylene solution in the presence of 1 percent by weight of boron trifluoride etherate catalyst; The reaction was carried out at a temperature of 155 C. and was continued for 17 hours. The resulting mixed ester was washed with 5 percent sodium hydroxide in water and then dried. The Total Acid Number of the mixed ester, expressed as milligrams of KOH per gram of the ester, was 4.5, against a calculated value of zero. The mixed ester contained 5.5% chlorine against a calculated value of 6.7% by weight. The product from this reaction was mixed with vinyl acetate'in a molar ratio of 1.4

moles of vinyl acetate per mole of ester in 50 percent by weight of benzene. One percent by weight of benzoyl peroxide was added to the solution as a catalyst and the reaction mixture was then exposed to 6 megaroentgens of gamma radiation at F. to elfect copolymen'zation.

EXAMPLE 8 The copolymers prepared in Examples 3,4, 5, 6 and 7 were incorporated at a concentration of 0.01% by weight of the 50% benzene solution into samples of a heating oil comprising a blend of about 50 percent virgin distillate and about 50 percent cracked stock. Typical properties of such a heating oil are as follows;

These samples and a sample of the base oil were subjected to an Accelerated Storage Stability Test which comprised heating the samples for a period of 16 hours at a temperature of 210 F. At the end of the 16 hour period the samples were filtered through a medium porosity sintered glass filter and the amount of sediment formed was determined.v

TABiE I Accelerated Storage Stability Tests V [Additive conc.=.01% of a 50% solution in benzene] Additive: Sediment, mg./ 600 g. oil None 1 12.7 Product of Example 3 1.2 Product of Example 4 ..i .i. 1.4 Product of Example 5 1.0 Product of Example 6 0.8 Product of Example 7 1.6

Reproducibility of test, :1 mg.

As shown by these data, the additives of the invention substantially reduced sediment formationin the oil.

EXAMPLEQ' The additives of the invention are effective in jet fuels as well as in middle distillate heating "oils; To demonstrate this, the products of Examples 3 and 4 were incorporated into samples of a'jet fuel covered by US. Mili tary Specification MIL-F-5624C which boiled between 300'and 550 F. Thesesamples were subjected to a CPR Fuel Coker Test. The tests were carried out by passing the samples through hot preheater tubes which brought the fuel temperature to400 F. The heated fuel was then passed througha sintered metal micronic filter heated; to a temperature of 500 F. The pressure drop acrossthe filter and the deposit formed onthe preheater tubes were measured 'for each sample and compared with the values obtained with the uninhibited fuel. Data from this test are shown in Table II.

1 A rating of 500 or above is considered good. 2 First number is percent tube covered, second 1s color of deposit: J=clear; 2=very light tan; 4=tan; 6=brown; 8=dark brown; 10=black.

EXAMPLE 10 To demonstrate the stabilizing action of the additives of the invention still further, fuel oil samples containing the products prepared in the previous examples and a commercial additive of the ashless type were subjected to an Accelerated FilterPlugging test by aging the samples for a period of 16 hours to a maximum temperature of 230 F. and then filtering them, The pressure drop across the filter pads, the weights of sediment recovered and the color ofthe sediment onthe padswere noted and compared. Table IV shows the results ob-' tained in this test.

TABLE III Accelerated Filter Plugging Test Demerit Rating Additive AP Visual Sedi- Overment all None 4 5 3 4. Product of Example 3 (0.00 0 0 1 0.8 Product of Example 3 (0.01 0 2 0 0. 7 Product of Example 4.(0.00 0 1 0 0. 3 Product of Example 4 (0.01 0 2 0 0. 7 Ploduct of Example 5 (0.01 0 1 0 0. 3 Product of Example 6 (0.01 0 1 0 0.3 Product of Example 7 (0.01%) 0 1 1 0. 7 Ashless Commercial'Additive 0 2 0 0.7

The test employed is described, in detail in New Fast Test Method for Distillate Storage Stability, by W. A. Konrad, N. L. Shipley and T. S. Tutwiler, which is found an page145v of Petroleum Processing, September 1956.

The lower the value of the overall demerit rating in this test, the better the stability properties of the oil. Again it :an be seen'that the additives of the invention produce a marked improvement in the stability of distillate fuels and in some respects are superior tocommercial additives It will be understood that the additives of the invention may be incorporated into petroleum distillate fuels inconiunction with other additives designed to correct other fuel deficiencies. The additives may also be used in the form of amine or other derivatives rather than as straight :opolymers. a

What is claimed is; V a

1. A copolymer of along chain saturated aliphatic alco 'sol-chloropropyleneoxy mixed ester of an unsaturated :onjugated dibasic acid, said acid having from 4 to 5 carbon atoms per molecule and a polymerizable organic rnonomer selected from the group consisting of (a) a vinyl ester of a short chainfatty acid and (b) a mixture of a vinyl ester of a short chain'fa'tty acid and along :hain saturated aliphatic alcohol ester of a conjugated unsaturated dibasic acid, said acidcontaining from 4 to 5 :arbon atoms per molecule, and wherein the mole ratio of said mixed ester-to said monomer is between 2: l and 1:20, and said copolymer has a molecular weight of from 3,000 :0 about 100,000. 2. A copolymer as defined in claim 1 wherein the saidv vinyl ester of a short chainfatty acid is vinyl acetate.

3.-Acopolymer as definedin claim 1 wherein said unsaturated conjugated dibasic acid isa butenedioic acid.

' 4. A copolymer as defined in claim 1 wherein said long chain saturated aliphatic alcohol is a straight chain primary alcohol containing from 8 to 24 carbon atoms per molecule. 5. A copolymer as defined in claim 1 wherein the said copolymer has a molecular weight ofbetween 6,000 and about 20,000.

' to about 1:4.

'7. An oil soluble copolymer of an alkyl C3 to C chloropropyleneoxy mixed ester of a butenedioic acid having a mixed ester to chloropropyleneoxy ratio of between 1 :1 and 1:4 and a monomer selected from the group consisting of (a) vinyl acetate and (b) a mixture of vinyl acetate and a C to C saturated aliphatic ester of a butenedioic acid, said copolymer having a mole ratio of mixed ester to monomer of between 2:1 and 1:20 and a molecular weight between 6,000 and about 20,000.

8. An oil soluble copolymer of an alkyl C to C chloropropyleneoxy maleate anda vinyl acetate, said copolymer having a mole ratio of maleate to acetate of between 2:1 and 1:20 and having a molecular weight of 6,000 to about 20,000.

9. An'oil soluble copolymer of an 'alkyl C to C chloropropyleneoxy maleate and a monomeric mixture of vinyl acetate and alkyl fumarate, said copolymer having a mole ratio of maleate to monomer mixture of between 221 and 1:20 and a molecular weight between 6,000 and about 20,000.

10. A copolymer of a long chain saturated aliphatic alcohol-chloropropyleneoxy mixed ester of an unsaturated conjugated dibasic acid, said acid having from 4 to 5 carbon atoms per molecule and styrene and wherein the mole ratio of said mixed ester to styrene is between 2:1

rated conjugated dibasic acid, said acid having from 4 to 5 carbon atoms per molecule and methyl methacrylate and wherein the mole ratio of said mixed ester to methyl methacrylate is between 2:1 and 1:20 and said copolymer has a molecular weight of between 3,000 and 100,000.

.12. A petroleum distillate fuel boiling in the range between about 300 F. and about 900 F. having incorporated therein a stabilizing amount of a copolymer of a long chain saturated aliphatic alcohol chloropropyleneoxy mixed ester of an unsaturated conjugated dibasic acid, said acid having from 4 to 5 carbon atoms per molecule and a polymerizable organic monomer selected from the group consisting of (a) a vinyl ester of a short chain fatty acid and (b) a mixture of a vinyl ester of a short chain fatty acid and a long chain saturated aliphatic alcohol ester of a conjugated unsaturated dibasic acid, said acid containing from 4 to 5 carbon atoms'per molecule, and wherein the mole'ratio of said mixed ester to said monomer is between 2:1 and 1:20, and said copolymer has a molecular weight of from 3,000 to about 100,000.

13. Arfuel composition as defined by claim 12 wherevin the concentration of said copolymer is from about in said mixed ester is Lorol-chloropropyleneoxy maleate.

15. A fuel composition as defined by claim 12 Wherein said vinyl ester comprises vinyl acetate.

16. A fuel composition as defined by claim 12 wherein said 'mixed ester is isooctyl chloropropyleneoxy maleate. 17. A fuel composition as defined by claim 12 wherein said mixed ester is tallow-chloropropyleneoxy maleate. 18. .A fuel composition as defined in claim 12 where! in said unsaturatedconjugated dibasic. acid is a butene dioic acid.

- 19. A fuel composition as defined in claim 12 wherein said long chain saturated aliphatic alcohol is a straight chain primary alcohol containing from 8 to 24 carbon atoms per molecule.

20. A fuel composition as defined in claim 12 wherein the said copolymer has a molecular weight of between 6,000 and about 20,000.

21. A fuel composition as defined in claim 12 wherein the mixed ester to chloropropyleneoxy ratio is between 1:1 to about 1:4.

22. A fuel composition as defined in claim 12 wherein said distillate fuel is a jet fuel boiling in the range between about 300 F. and about 550 F.

23. A petroleum distillate fuel boiling in the range between about 300 F. and about 900 F. having incorporated therein from about 0.002 to about 2.0% by weight of an oil soluble copolymer of an alkyl C to C chloropropyleneoxy mixed ester of a butenedioic acid having a mixed ester to chloropropyleneoxy ratio of between 1:1 and 1:4 and a monomer selected from the group consisting of (a) vinyl acetate and (b) a mixture of vinyl acetate and a C to C saturated aliphatic ester ofa butenedioic acid, said copolymer having a mole ratio of mixed ester to monomer of between 2:1 and 1:20 and a molecular weight between 6,000 and about 20,000.

24. A petroleum distillate fuel boiling in the range between about 300 F. and about 900 F. to which has been added from about 0.005 to about 0.1 percent by weight of a copolymer of a mixed ester of tallow-chloropropyleneoxy maleate with an organic monomer mixture of 1 mole of vinyl acetate and 0.75 to 0.875 mole of tallow fumarate and wherein the mole ratio of ester to monomer is between 2:1 and 1:20, said copolymer having a molecular weight of from about 6,000 to about 20,000 Staudinger.

25. A petroleum distillate fuel boiling in the range between about 300 F. and about 900 F. to which has tween about 300 F. and about 900 F. to which has been 1 added from about 0.005 to about 0.1% by Weight of a copolymer of a mixed ester of Lorol-chloropropyleneoxy maleate' with an organic monomer of vinyl acetate wherein the mole ratio of ester to monomer is between 2:1 and 1:20, said copolymer having a molecular weight of from 6,000 to 20,000 Staudinger.

References Cited in the file of this patent UNITED STATES PATENTS 2,402,863 Zuidema et a1 June 25, 1946 2,448,531 Kenyon Sept. 7, 1948 2,524,432 Dorough Oct. 3, 1950 2,539,438 Kropa et al. Jan. 30, 1951 2,607,761 Seymour Aug. 19, 1952 2,615,845 Lippincott Oct. 28, 1952 2,626,945 Carlin Jan. 27, 1953 2,642,414 Bauer et al. June 16, 1953 2,800,401 Lusebrink et a1. July 23, 1957 OTHER REFERENCES Industrial and Engineering Chemistry, vol. 41, No. 17, July 1949, Copolymers of Vinyl Compounds and Maleic Anhydride, by Seymour et al., pages 1509-1513.

Claims

12. A PETROLEUM DISTILLATE FUEL BOILING IN THE RANGE BETWEEN ABOUT 300*F. AND ABOUT 900*F. HAVING INCORPORATED THEREIN A STABILIZING AMOUNT OF A COPOLMER OF A LONG CHAIN SATURATED ALIPHATIC ALCOHOL-CHOLORPROYLENEOXY MIXED ESTER OF AN UNSTATURATED CONJUGATED DIBASIC ACID, SAID ACID HAVING FROM 4 TO 5 CARBON ATOMS PER MOLECULE AND A POLYMERIZABLE ORGANIC MONOMER SELECTED FROM THE GROUP CONSISTING OF (A) A VINYL ESTER OF A SHORT CHAIN FATTY ACID AND (B) A MIXTURE OF A VINLY ESTER OF A SHORT CHAIN FATTY ACID AND A LONG CHAIN SATURATED ALIPHATIC ALCOHOL ESTER OF A CONJUGATED UNSATURATED DIBASIC ACID, SAID ACID CONTAINING FROM 4 TO 5 CARBON ATOMS PER MOLECULE, AND WHERE THE MOLE RATIO OF SAID MIXED ESTER TO SAID MONOMER IS BETWEEN 2:1 AND 1:20, AND SAID COPOLYMER HAS A MOLECULAR WEIGHT OF FROM 3,000/ TO ABOUT 100,000.